Signs of Summer 9: More on Coffee

Photo by J. Scortzman, Flickr

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Coffee is, to me, one of the glorious aspects of life and living. The small trees and bushy shrubs of the genus Coffea yield “cherries” (red to purple, pulpy fruits) that contain the caffeine and flavor-rich seeds (the coffee “beans”) that can be roasted and ground up and then brewed into the wonderful, black beverage that so many of us love.

There are 124 species of Coffea and most grow wild in sub-Saharan Africa. Only two of these species are extensively cultivated to produce commercially traded coffee. Coffea arabica (“Arabian coffee”) makes up 60 to 70% of the coffee grown and sold around the world, and Coffea robusta makes up the remaining 30 to 40%. A study by botanists at the Kew Garden (“Royal Botanical Gardens”) in Great Britain, published earlier this year in both Science Advances and Global Climate Change Biology, determined that 60% of the wild Coffea species are at risk of extinction due to climate change and habitat destruction. The potential loss of this diverse and as yet poorly studied gene pool could leave cultivated coffee without the genes and proteins that it needs to survive in our climate changed world!

Coffea arabica was the first type of coffee to be domesticated. By the early Sixteenth Century it was widely consumed throughout the Middle East. It is native to the southern highlands of Ethiopia and arose, apparently, as a naturally occurring hybrid of two other Coffea species (C. robusta and C. eugeniodes). Most Coffea species have diploid chromosome arrangements, but C. arabica is tetraploid and contains the entire genomes of both C. robusta and C. eugeniodes.

Coffea arabica.Photo by H. Zell. Wikimedia Commons

In its natural habitat, C. arabica grows as an understory plant beneath tall shade trees. It is capable of self-pollination and relies primarily on wind dispersal of pollen (although wild bees greatly increase its overall pollination efficiency both in wild and domesticated systems). The traditional method of cultivation of C. arabica, which is practiced in more than 70 countries around the world, replicates this controlled, shady, growing environment.  In modern parlance this type of coffee growing system generates “shade grown” coffee beans. Coffee trees in shade grown coffee plantations can produce coffee beans for 30 years or more!

In the 1970’s, though, in an attempt to increase the productivity of coffee trees, sun tolerant varieties of Coffea were developed. Coffee could then be grown in vast, open, monocultural plantations that produced what is now called “sun grown” coffee beans. Sun grown coffee systems do have higher yields per tree, but its trees are only productive for about 15 years.

Sun grown coffee plantation in Kaua’i Hawaii. Photo by Lukas. Wikimedia Commons

Sun grown coffee was beset with a myriad of other problems, too. Increased levels of fertilizers, pesticides and herbicides were needed to fuel the increased productivity of the coffee trees and to fight intrusions of insect pests and weeds. Also, removal of the shading, over-story trees destroyed important habitats for a large number of native birds, mammals and reptiles (many of which were quite active in insect control!). A study published last year counted 204 species of birds living in the shade grown coffee plantations in the Western Ghats of India.

Removal of the protective tree cover also exposed soils to the often violent rain storms of the tropics and led to accelerated rates of soil erosion. Also, the quality of the coffee suffered. The accelerated coffee bean maturation rate in the sun grown trees generated beans with lower levels of important flavoring chemicals and higher levels of increasingly bitter acids. It was a lose/lose/lose/lose proposition! In Central America alone, over 2.5 million acres have been deforested to make room for sun grown coffee plantations.

Coffea robusta is particularly well adapted to sun grown coffee systems. Its flavor profiles are not as high in quality as those of C. arabica, but its higher caffeine content makes it a desirable crop. Many sun grown coffee plantations are dominated by C. robusta trees. Interestingly, C. robusta trees are not self-pollinating. They require the spread of pollen from one tree to the next and are much more dependent on insect pollen transfers than C. arabica. The monocultural nature of the sun grown coffee plantations, though, and their inherent dearth of nectar producing wild plants coupled with the extensive use of pesticides in the management of the system greatly reduced the abundance of potentially beneficial pollinating wild insects.

Shade grown coffee in Guatemala. Photo by J. Blake. Wikimedia Commons

Coffee trees of all types need stable environments to grow and thrive. This has been one of the ongoing arguments in favor of planting coffee trees in shade coffee systems. The micro-environments of the shade plantations fluctuate much less than they do in sun grown coffee systems. These more controlled environments may even serve as buffers against some of the predicted temperature and moisture consequences of climate change. The need for consistent growing conditions is also one of the explanations for the superiority of high altitude grown coffee over most low altitude grown coffee. Cooler, less fluctuating temperatures and lower atmospheric oxygen levels slow down the coffee tree’s rates of synthesis and maturation and enable the high altitude grown beans to develop their full flavor profiles and potentials.

Back in 2017 I wrote about some very disturbing studies concerning the sustainability of coffee cultivation. A report by the Climate Institute of Australia explored the impact of climate change models on the global distribution of coffee trees. They found that projected rises in global temperatures would reduce coffee producing land areas by 50% by 2050. Impact of climate change (which includes not only rising average temperatures but also changes in weather patterns and cycles of drought and excessive rainfall) were especially severe at low latitudes and low altitudes. The worldwide, tropical “bean belt” will need to move out of the afflicted tropical zones and up mountainsides in order to find suitable sites to grow coffee. It is estimated that there are 120 million people in these zones whose economic livelihoods depend on coffee.

The recent awareness of the multiple benefits of shade coffee have included not only an economic side (lower production costs), an ecological side (reduced pollution and soil erosion and establishment of complex habitats for birds and other animals), and also an aesthetic side (shade grown coffee tastes better!). Climate change, though,  may be too much even for these coffee ecosystems unless new genetic traits from the wild Coffea species can be found to extend coffee trees’ growth tolerance ranges into the “new normal” of our climate changed world.

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Signs of Summer 8: Among Hemlock Trees

Photo by D. Sillman

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I am standing in the middle of an old growth hemlock stand that is tucked away off a hiking trail in Laurel Hill State Park. This four acre plot probably escaped logging because of confusion about the exact location of a surveyor’s line. Cutting a tree on someone else’s property was an expensive mistake (fines and reimbursement of the owner of three times the value of the logged trees and, possibly, even penalties for trespassing!). So, to avoid doing all of the work and only getting the privilege of paying many times over for it, disputed property lines often generated safe zones for fragments of primal forest.

Many of the hemlocks around me are impressively large. A few measure nearly four feet in diameter and stand one hundred feet tall. According to Kershner and Leverett  (2004) these trees range between 200 and 300 years of age. So, they are not even half way along on their potential life spans of 800 to 1000 years. There is a range of tree diameters and heights within the stand, which, I assume, reflects a distribution of ages.

The forest floor is covered with a thick layer of shed hemlock needles. Deep in the litter layer a slow process of decomposition is going on. The very top needles are relatively dry, but layers just below and on down to the soil surface are increasingly moist. The soil is black and wet. The thick, acidic mulch layer prevents many understory species from growing here. There is an open quality to this part of the forest. It is very easy to walk around. The mulch underfoot is soft and springy. Wood sorrel, wood fern, club moss, and polytrichium moss grow in scattered patches, and radiating out away from the hemlocks is a three dimensional cone of scattered and ever smaller hemlock seedlings.

Photo by Bonnachoven, Wikimedia Commons

The reality of this hemlock stand is an emotional experience. Intellectually, though, I know that these slopes of Laurel Hill were once densely covered with often pure stands of hemlocks trees, and I also know that these hemlocks were cut down in the late 1800’s and early 1900’s for their wood and to harvest their bark tannins. The clear-cut slopes, thanks to the resilience of Pennsylvania’s vegetative communities, reforested themselves in fast growing hardwood trees like red maple and black cherry and stump sprouting red oak but not, immediately, in hemlocks. Standing among these few surviving trees humbles my imagination to try to visualize what this primal forest was like. Contemplation of the immensity of the individual trees, the impact of the stand on the very climate of the site, and the overwhelming continuity of the former forest is awe inspiring. This a beautiful spot, but what a place it once was!

So, why were hemlock trees here? Why did this forest grow, and, very significantly, why is it growing back so slowly? To try to answer these questions, let’s start at the beginning of a single tree and imagine its life over several hundred years:

Photo by N. A. Tonelli, Flickr

To get a hemlock, you have start with a hemlock (to paraphrase Schleiden and Schwann’s Cell Theory statement, “omnis hemlockae et hemlockae” (“hemlocks always come from hemlocks”)). So, a mature, seed-producing hemlock had to have been right here because hemlock seeds do not travel very far from their parental tree source (Goldman and Lancaster 1990). Therefore, the parental trees of the hemlocks around me themselves stood very close to this very same spot. And, the parental trees of those trees, and their parents’ parents’ parental tree, and so on, were also right here or at least very close by. The generations of trees were separated by centuries or even millennia of time, but all of these trees stood trunk to trunk and branch to branch in this very space.  Where we see a hemlock forest there has been a hemlock forest for a very long time.

The parental tree of our example hemlock could have started to make cones when it reached 15 years of age, but if it were growing in the deep shade, reproduction might actually have begun much later on in its life. A hemlock can grow so slowly for one or two hundred years when light deprived that it scarcely makes growth rings (Tubbs 1977). In this suppressed state, energy is used to maintain existence with little left over for growth or reproduction. Removal of the shade suppression (say, when an older, nearby tree succumbs to disease, is thrown over in a wind storm, gets struck by lightning, or simply reaches the end of its possible life span) stimulates the young tree to rapidly grow and eventually reach its reproductive maturity..

Photo by K. McFarland, Flickr

Each hemlock tree has both male and female cones. The male cones’ pollen is dispersed by the wind and mostly falls in places where it will dry up and inconsequentially fail. A very small percentage of these shed pollen grains falls into the open scales of the upwardly directed ovulate cones and are thus given the opportunity to fertilize an ovum. Most of these pollen grains, though, even when they are “lucky” enough to be blown into an ovulate cones, also dry up and fail to accomplish fertilization (Nienstaedt and Kriebel 1955).

So, an infinitesimally small percentage of the pollen grains produced actually fertilize ova inside the female cones and make viable embryos and seeds! When fertilization does occur, the ovulate cone closes its scales around the seed and turns from its upward orientation to a downward, dangling position. The cone grows and then, as it and its seeds mature, turns from an initial yellowish green to purplish brown and then, as it dries, to a deep, dark brown. In mid-October the cone opens, and the seed, with its short, terminal wing, flutters downward to the litter surface probably just beneath or at least very close to the parental tree (USDA Forest Service 1974).

Photo by D. Sillman

Eastern hemlocks make cones frequently (two out of every three years) and a single tree can continue to make cones well into its fifth century of life (USDA Forest Service 1974). That’s a lot of cones and a lot of seeds! Very few of these seeds, though, ever get the chance to become a tree. Many of the seeds are eaten (by rodents, by insects, by squirrels)(Abbott 1962), many of the seeds dry out on the dry surface of the litter, and many others rot away when the litter layer is too wet (Le Madeleine 1980). Conditions have to be just right for seed survival. Many surviving seeds then don’t germinate because the ten week rest period at freezing temperatures didn’t occur so their dormancy was never released. Many other seeds don’t germinate because the temperatures after the dormancy release are too cold or too warm (optimally it should be 59 degrees F, but a range of 44 to 65 degrees F is tolerable). A very precise micro-environment on the forest floor is required to give the hemlock seed its shot at germination!)(Goldman and Lancester 1990). So, a massive number of seeds are needed to get just a couple of them through this dense ecological filter of catastrophic probabilities.

The seeds that germinate might have landed on a mound of soil and litter or maybe on a rotting stump or a rotting tree trunk. Its overstory must keep it shaded, though. Any increase in sunshine on the germination site will increase the rate of moisture loss and will quickly kill the seed or the seedling (Jordan and Sharp 1967).

After a year of growth the seedlings would be about one inch tall with a half an inch of roots extending down into the moist layers of the litter. The upper half inch of litter is very vulnerable to drying so even short period of drought can kill these young seedlings. Any seedling not in the deep shade, or any seedling not growing on a moist enough pile of litter will die (Goldman and Lancaster 1990).

By the second year, the seedling’s roots have extended deep enough into the litter layer that moisture delivery is more assured. The seedling’s chances of survival and ability to grow have greatly increased. Hemlock seedlings, as I mentioned before, can survive in deep shade. Even in conditions in which only 5% of full sunlight is available to the seedling, enough photosynthesis can occur to keep the seedling alive if only barely growing, and the seedling can persist in this state of suppression for one or two centuries (Tubbs 1977)!

When the seedling is 3 to 5 feet tall it is able to withstand the impacts of full, direct sunlight (Gladman and Lancaster 1990). Hemlocks an inch in diameter can be a hundred years old and some that are two or three inches in diameter can be 200 years old (Tubbs 1977)! The tiny trees we see growing around the parental hemlocks in our Laurel Hill site may have been growing and waiting for a very long time.

Photo by Pixabay, Public Domain

These young trees are very vulnerable to tree predators. White tailed deer readily browse young hemlocks as do cottontail rabbits and snowshoe hares (Abbott 1962, Anderson and Loucks 1979, Euler and Thurston 1980, Goldman and Lancaster 1990). The probabilities are very high that in the many decades the young trees sit well within reach of these browsing animals they will be consumed. And hemlocks are not capable of root sprouting (USDA Forest Service 1965), so destruction of the above ground mass results in the death of the tree.

But some trees, somehow and against all probabilities, survive all this, and are present when a light gap opens (a large, shading tree (maybe the young tree’s parental tree?) is wind thrown, struck by lightning or killed by defoliators or diseases). The opening of the overstory then allows young tree to rapidly grow.

Centuries pass. Our tree has steadily grown and is now nearly four feet in diameter and one hundred feet tall. It dominates its space in the forest and rains down seeds onto the forest floor around it every two out of three years. As mentioned previously, a very small number of these seeds ever germinate, and an even smaller number of the seedlings ever grow, but there is a slow, steady wave of hemlock seedlings growing out from around each of the seed producing trees. The limited, seedling nurturing micro-environments under the parent trees slowly expand as the parent trees grow. The seedlings are also encouraged or destroyed by the temperature and rainfall fluctuations of their growth site’s weather and climate patterns.

Photo by W. Hamilton

Hemlock forests grow from hemlock forests. The old trees are needed not only for seeds but also for the control of the forest floor environment. The slow recovery of a logged hemlock forest reflects the very slow return of the influence of the mature trees on the seedling nursery of its forest floor.

Are small hemlock stands like this one in Laurel Hill State Park sustainable? Can they continue to extend themselves at their edges and begin to knit together their old range and scope? Can they be “ecological crystals” that reform the old growth, hemlock forest? Looking at the edges of this site, I see hemlock needles mixing with fallen maple leaves and the slowly growing, outward curve of spreading hemlock seedlings.  I see the beginnings of some possibilities. Hemlocks live in time frames that are so very different from short-lived species like humans. What will happen here? I’ll get back to you in five hundred years and let you know how it’s going.

References for Eastern Hemlock:

Abbott, H. G. 1962. Tree seed preferences of mice and voles in the Northeast. Journal of Forestry 60 (2): 97-98.

Anderson, R. G. and O. L. Loucks. 1979. White-tail deer (Odocoileus virginianus) influence on structure and composition of Tsuga canadensis forests. Journal of Applies Ecology 16: 855-861.

Eckstein, R. G. 1980. Eastern hemlock in north central Wisconsin. Wisconsin Department of Natural resources, Report 104. Madison. 20 p.

Euler, D. and L. Thurston. 1980. Characteristics of hemlock stands related to deer use in east central Ontario. Journal of Applied Ecology 17:1-6.

Eyre, F. H. (ed) 1980. Forest cover types of the United States and Canada. Society of American Foresters, Washington, D.C. 148 p.

Goldman, R.M. and K. Lancester. 1990. Tsuga canadensis (L.) Carr: Eastern Hemlock. pp 604-612, In, Burns, R. M. and B. H. Honkala (tech coord) “Silvics of North America: Volume 1, Confers.” U.S. Department of Agriculture, Agriculture Handbook 654. Washington, D. C.675 p.

Hepting, G. H. 1971. Diseases of forest and shade trees of the United States. U.S.Department of Agriculture, Agriculture Handbook 386. Washington, D.C. 658 p.

Hough, Ashbel F. 1960. Silvical characteristics of the eastern hemlock. USDA Forest Service, Station Paper NE-132. Northeast Forest Experiment Station, Upper Darby, PA. 23 p.

Jordan, J.S. and W.M. Sharp. 1967. Seeding and planting hemlock for ruffed grouse cover. USDA Forest Service, Research Paper NE-83. Northeastern Forest Experiment Station, Upper Darby, PA. 17 p.

Kershner, B. and R. T Leverett. 2004. The Sierra Club Guide the Ancient Forests of the Northeast. Sierra Club Books. San Francisco.

LeMadeleine, Leon. 1980. Seed-borne pathogens of hemlock seed from Argonne Experiment Forest. Evaluation Report NA-FB/U-8, January. U.S.Department of Agriculture, Forest Service, Northeastern Area State and Private Forestry, St. Paul, MN. 4 p.

Nienstaedt, H. and H.B.Kriebel. 1955. Controlled pollination of eastern hemlock. Forest Science 1(2): 115-120.

Rogers, R.S. 1980. Hemlock stands from Wisconsin to Nova Scotia: transitions in understory composition along a floristic gradient. Ecology 61(1): 178-193.

Tubbs, C. H. 1977. Manager’s handbook for northern hardwoods in the north Central States. USDA Forest Service, General Technical Report NC-39. North Central Forest Experiment Station, St Paul, MN. 29 p.

U.S.Department of Agriculture, Forest Service. 1974. Seeds of woody plants in the United States. C.S.Schopmeyer, tech. coord. U.S. Department of Agriculture, Agriculture Handbook 450. Washington, D.C. 883 p.

Willis, G.L. and M.S.Coffman. [n.d.] Composition, structure, and dynamics of climax stands of eastern hemlock and sugar maple in the Huron Mountains, Michigan. Michigan Technical University, Department of Forestry, Technical Bulletin 13, Houghton, 43 p.

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Signs of Summer 7: Reduce, Reuse, Recycle

Public Domain

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Some personal history: Deborah and I have recycled our household materials for as long as I can remember. Decades ago, this was a very difficult process. We had to separate plastics and paper, aluminums from other metals and had to be sure that the cardboard was clean (no used pizza boxes!) and that all cardboard boxes were broken down and flattened. We also had to separate the different colors of glass and make sure that everything was completely clean. For a while we even had to remove all of the labels from the glass and the metal cans (an often tedious and energy intensive process!)!

Once a month or so I would take the plastics and the non-aluminum metals and the cardboard to one recycling place, the paper to one of the big bins located in a nearby parking lot,  the aluminum to a Boy Scout sponsored bin down near the highway, and the glass to a glass reprocessing plant over across the Allegheny River. Lots of running around, and lots of time and energy invested and expended.

Many of the larger towns around us (under pressure from new state laws mandating recycling) began curbside recycling programs in association with garbage pickup. The town in which we lived, though, was too small to be compelled to initiate one of these programs, so we kept at our self-motivated system for well over a decade.

A friend pointed out the energy cost of all of my cleaning, sorting and transporting of these recyclables more than erased the benefit of the recycling, but the closure of our materials-loop made it seem worthwhile to me. My family produced just a single bag of garbage a week and, so, were not adding substantially to the mountains of trash growing in area landfills. We were as close as we could get to living in a stable dynamic with our world.

Photo by U.S. E.P.A.

Then recycling came to my small town in the form of a twice a month visit by the recycling trucks manned by volunteers from the nearby Progressive Workshop. The trucks had compartments for all of the different materials, and we took ours down every other truck-visit day or so for the next 10 or 12 years. We still had to separate materials (including the different colors of glass) and they still did not want food-soiled cardboard (we were eating a lot of pizza back then, too! Too bad.), but the recycling truck’s proximity greatly reduced my recycling-transportation system’s gasoline costs. Again, there was something so satisfying about returning all of those cans, bottles, newspapers (yes, we read actual, paper newspapers back then!), and plastic doohickeys back into a system where they could be re-processed and reused.

Then there were budget problems and the trucks stopped coming. Back to our old recycling route? No, something even better (or something that seemed so much better) came into being.

Photo by M. Buckawicki, Wikimedia Commons

Deborah and I both taught at Penn State New Kensington, and the campus, working with its waste collections system provider, began a single-stream recycling program and encouraged campus employees to bring their recyclables up to campus and deposit them in the recycling dumpster.  There were some restrictions: types of plastics, cleanliness of cans and jars, cardboard boxes had to be broken down and still no used pizza boxes were accepted (but we were eating much less pizza by this time!).

Deborah and I set up a single recycling receptacle in our kitchen and bought the clear, recycling bags (we learned from a trip to the single-stream processing plant that opaque trash bags were not acceptable for recyclable materials. Frequently, materials in these type of bags were simply thrown into the garbage by the initial sorting crew. They were being very cautious to keep garbage out of their system!). We were very careful with our types of plastics and only put clean cans and jars into the bin. Paper, cardboard, aluminum and everything else all went into one bag. Every few weeks I took the bags up and tossed them into the recycling dumpster.

It was so easy! It seemed too good to be true! And, it turned out that it wasn’t true! There were problems with single-stream and also problems with having unsupervised people depositing materials into the recycling stream.

The dumpsters frequently were filled up with boxes that had not been broken down and flattened. Also, odd, large objects that were quite obviously trash were tossed in with the recyclables. The recycling company also had a list of some potentially recyclable materials that they did not want in their recycling stream: small, plastic containers (yogurt containers, for example) and plastic bags (like grocery bags) were not on the acceptable material list because of their tendency to clog the sorting machinery at the single-stream plant. Apparently, though, not everyone paid attention to the change notices and many bags were full of these banned materials. I also noticed that many of the bags tossed into the recycling dumpster were those dark, opaque trash bags that the sorters didn’t want us to use!

The recycling collector fined Penn State because of these unacceptable materials and packages and, eventually, the cost of providing recycling to employees and the public became prohibitive. So Penn State put a lock on the recycling dumpsters and only used them for campus generated materials. About this same time the single-stream, recycling provider who is also the principle recycling entity for most of the community-based recycling programs in Western Pennsylvania, announced that they would no longer accept glass.

Photo by ShoZu, Flickr

Glass is an interesting material in recycling. First and foremost, it is without a doubt the most easily and almost infinitely recyclable material there is! Glass bottles and jars made from recycled materials are exactly the same as glass bottles and jars made fresh from natural, virginal resource materials, and they cost 90% less to make! There is no limit to the number of times glass can be used, recycled, re-processed and then re-used. But, glass is also heavy and can be costly to transport. If you happen to live in a city where there is no glass reprocessing plant, you may not be able to recycle your glass!

Western Pennsylvania, though, has a well established infrastructure for glass reprocessing. The reason that the single stream processor was no longer accepting glass had to do with the nature of the single stream itself. Glass in the mixed bag of recyclables frequently broke and then contaminated the other materials. Glass shards in the paper, or in the cardboard or in the plastic were hard to remove and made those materials less desirable to their end processors. Glass was making the single stream company lose money, so they banned glass.

There have been many levels of response to these changes. A few friends of mine have just stopped recycling. Single-stream was just so easy, it is hard to go back to the old sorting and hauling ways! Other friends switched back to their community, “glassless” recycling, and are doing their best not to buy products in glass containers. What glass they do accumulate they simply throw away. In Pittsburgh several groups have sponsored a series of “pop-up” glass recycling events. People save their glass materials until one of these recycling events is held near them, and then they take their glass to the event and add it to the recycling stream.

Deborah and I have found a local recycling group in a nearby town. They take all recyclables but require that glass, metal, aluminum, paper, cardboard and plastic (only #1’s and #2’s) be separated and sorted. We have set up a series of bins and boxes in the basement to store our sorted recyclables. Every four or five weeks, I take a carload over to the recycling center (they are open weekday mornings. No problem for us retired folks!) and drop them off. The volunteer workers at the center are friendly and helpful, and last time they even let me dump my own glass into the crushing machine! VERY satisfying!

Photo by D. Graham, Flickr

So, we’re back to almost where we started in personal recycling! Clean and sorted, carried to the center and deposited. Used pizza boxes, by the way, are still not accepted! I do have a garage full of them if anyone comes up with a use!




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Signs of Summer 6: Gypsy Moths and Tent Caterpillars

Gypsy moth adult female. Photo by Opuntia, Wikimedia Commons

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Riding my bike down on Roaring Run back in June, I had to keep my eyes on the path immediately beneath my tires rather than on the much more interesting woods around me.  Crawling across the gravely surface of the trail was a mixed parade of forest millipedes and gypsy moth caterpillars, and it took all of my attention to avoid running them over.

Gypsy moths (Lymantra dispar) were/are one of the great invasive scourges of our eastern forests. A brief review of their history: they were brought to North America (Medford, Massachusetts to be precise) in 1869 by Etienne Leopold Trouvelot who intended to breed them with Asian silk moths so that he could develop a domestic silk industry. The gypsy moths escaped from Trouvelot’s home and quickly became a recognized pest in the oak forests of New England. In 1906 the U.S Department of Agriculture released an exotic, European, parasitic, tachinid fly (Compsilura concinnata) to try to get the exploding gypsy moth populations under control. Over the next eighty years the USDA repeatedly released more and more of these tachinid flies throughout affected forests in a vain attempt to control the spreading gypsy moths. As pesticides were invented, they were thrown at gypsy moths, too. Pathogenic fungi were also developed and used to weaken and reduce the gypsy moth masses.

Gypsy moth caterpillar. Photo by D. Descouens, Wikimedia Commons

Those of us of who remember the gypsy moth outbreaks here in Western Pennsylvania in the early 1990’s can recall trees covered with writhing masses of caterpillars, and sidewalks, streets, and driveways coated with crushed caterpillars. We also remember that we had to wear hats when walking in the woods because of the constant raining down of tiny fecal pellets from the swarms of gypsy moth caterpillars feeding on leaves up in the tree canopies. Many oak trees were completely defoliated. Many oak trees were killed. But, then the explosive numbers died back and for most us “went away.”

There are still significant areas of Pennsylvania where gypsy moths are an overwhelming pestilence, but many more areas of forest where they have become a baseline part of a tolerable equilibrium. Maybe the pathogenic fungus was the key weapon for control. Maybe letting the population become so dense triggered a crash from which the species has not yet recovered. Either way, biking along Roaring Run Trail and dodging a few crossing gypsy moth caterpillars is so much better than the slipping and sliding over thousands of their crushed carcasses just 25 years ago!

Last year (2018) the Pennsylvania Department of Conservation and Natural Resources sprayed forests in eight counties in northeastern and central parts of the state in an effort to control gypsy moth outbreaks. The war against the gypsy moth, then, is far from over!

Unfortunately, though, there is a great deal of collateral damage from many of the biological control systems that have been unleashed on the gypsy moths. Those tachinid flies in particular that were released during eighty years of fruitless attempts at biocontrol became established in North America and are doing a great deal of harm.

Let’s think about these parasitic flies and how they interact with their host caterpillars. First, many parasites of moth caterpillars lay their eggs on the surface of the skin of the larvae. Since larvae go through a number of growth and skin shedding stages (their “instars”) many of these surface eggs are in fact shed with each instar molt. Also, many of the moth parasites are very specifically matched to a species of moth caterpillars. Consequently, the parasite becomes active only during the seasonal activity time of the host caterpillar and has a very focused and direct impact on a specific moth species. These two features of the host/parasite interactions enable both species to reach equilibrium populations in which persistence of both species without explosive growth are achieved.

Cycle of fly parasitism in gypsy moths. Photo by Bugboy52.40, Wikimedia Commons

Compsilura concinnata, our introduced tachinid fly, however, exhibits none of these focusing or restraining parasitic features. This tachinid fly inserts its eggs into the body of a host caterpillar. No skin molting will shed the lethal parasite egg load once they have been delivered to the caterpillar. Also, this tachinid fly displays the antithesis of host specificity. It parasitizes nearly two hundred species of Lepidoptera (moths and butterflies) and Coleoptera (beetles) and Symphyta (sawflies) in North America alone. Further, C. concinnata instead of having its life cycle timed to the seasonal cycle of a particular host is able to have up to four generations in a single year. Each generation will encounter different butterfly, moth, beetle or sawfly species and have deleterious impacts on each of them.

Luna moth (male). Photo by David notMD, Wikimedia Commons

There was, then, no targeting of C. concinnata on gypsy moths! Almost every native moth and butterfly species in North America was exposed to this aggressive, generalist parasite! Monarch caterpillars are killed by C. concinnata, as are luna moths, cecropia moths, polyphemus moths and promethea moths. The decline of these “giant silk moths” in particular has been observed throughout their North American ranges, and some experts feel that C. concinnata is responsible for over 80% of their population loss!

Looking up from the gypsy moth caterpillars on the bike trail path I notice that the masses of tent caterpillars (Malacosoma americanum) are growing especially thickly on the terminal branches of the cherry trees all along the trail. These caterpillars are an inevitable sign of late spring, and, while they are not as beautiful as some of the other aspects of the season we have mentioned in the past, they are the principal food of one of the glorious birds in our area: The Baltimore Oriole. As I wrote in a blog several years ago:

Eastern tent caterpillars. Photo by J.R.Carmichael. Wikimedia Commons

“The oriole males are vying with each other for prime breeding territories and are getting ready for the anticipated arrival of the females. Baltimore orioles (and this species is distinct from Bullock’s oriole so recent attempts to lump both species together as the “northern oriole” are not valid) spend their winters in southern Mexico and Central America and then in the spring spread themselves out across their breeding territories in the United States from North Dakota to Maine and Oklahoma to the Carolinas.”

The orioles time their mating and egg laying and nestling emergence to the abundance of the eastern tent caterpillars! Fast food for fast growing nestlings! As John Irving once wrote in his novel “The Cider House Rules,” “be of use!” He could have been describing these tent caterpillars!

So, caterpillars are all around us! Some are vestiges of a colossal, human-generated disaster and others are enmeshed into natural trophic networks and serve as the primary fuel for some glorious baby birds. Sunlight to leaves to caterpillars to majestic orioles: it sounds so simple.

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Signs of Summer 5: Gray Tree Frogs

Photo by National Park Service

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As April transitioned into May it had finally gotten warm enough in the evening for Deborah and I to sit out on our deck. Late spring is a great time of year to sit outside in the developing darkness: there are no swarms of summertime mosquitoes yet, and the evening is full of great sounds. The robins are singing their nightly roosting songs, and the cardinals and the wrens are singing their territory songs. Also the leaves on the trees that encircle the deck are getting large enough that they have begun to seal off and hide our sitting space. Sitting very still we feel like we have become part of action around us!

Another song popped up into the night time concert a couple of weeks ago. It was a chirping, whirling song from many, widely scattered voices. The song started as the daylight began to fade and kept up all through the night. Every year the same thought process crawls through my conscious brain when I hear this song: what kind of bird is that? That’s not a bird! Is that a raccoon? What IS that? Oh, yeah …. Tree frogs!

The gray tree frog (Hyla versicolor) is a close relative of the spring peeper (Hyla crucifer (which is now more properly called “Pseudacris crucifer”)). We heard the choruses of the spring peepers back in March. The gray tree frogs emerge from their hibernation sites down in the leaf litter and wet, woody debris later in the spring than the peepers and use their larger body size (they are 1.5 to 2 inches long compared to just an inch for the peeper) to generate a louder, deeper, more resonant song. As with the peepers the male tree frogs are the ones doing the singing. The male tree frogs, though, are primarily solitary (as compared to communally chorusing peepers) so their songs are not as organized or as synchronized as the peepers’ “compositions.” Like the peepers, the tree frogs are trying to impress and attract their females to meet them in their surrounding ponds and puddles of water in order to mate. Their singing can go on for weeks or sometimes a month or more!

The gray tree frog is found throughout the eastern United States. It lives in trees and shrubs around ponds or seasonal wetlands. Although they are called “gray” they actually can have a range of colors from almost black to a very light green or even white. They can also change their skin color to match their surrounding substrates. These frogs are very good at camouflage (and are, subsequently, very difficult to find!). Their skin has more warts than a typical frog (but fewer than a typical toad!). They also have yellow patches on the inside of their back legs which are visible when they jump. The males have dark colored throats, and the females have white colored throats.

Photo by Fredlyfish4, Wikimedia Commons

If a male successfully draws a female into his mating area, the smaller male will cling to the back of the female (an arrangement called “amplexus”) and wait for her to release her eggs into the water of the pond or puddle. He then releases his sperm and fertilizes the eggs. Small clusters of the fertilized eggs stick to the water plants and hatch into tadpoles after three to seven days. After six to eight weeks of aquatic life, the tadpoles metamorphose into froglets that hop up into the surrounding vegetation in search of very small insects. The rapid, early life development of this species probably reflects the transient nature of its mating habitat’s water sources! There is a distinct rush to get onto land as quickly as possible!

The gray tree frog has mucous secreting pads on its toes. These sticky toe pads enable it to cling tightly to tree bark and climb easily through its arboreal habitat. It is a voracious, nocturnal predator of insects and can sometimes even be found outside a lighted window of house (sometimes even sticking onto the window!) feasting on the flying insects that are attracted to the light. They are very active up in the branches of trees and shrubs and jump from limb to limb in pursuit of prey.

The evening chorus of the gray tree frogs is still going on around my house although its intensity is waning. In a wet summer (and we are having a VERY wet summer!), the songs can go on well into early July. Over the past six or seven years, I have had more and more tree frogs in my spring and summer months. I think that the scattered leaf piles I have been leaving around many of my trees might be very good hibernation sites! The small creek down in my lower woods is keeping the spring pools around it full enough to support the tadpoles. Our abundant rainfall this year should keep the creek flowing on through the summer.

Photo by L. A. Dawson, Wikimedia Commons

The eastern gray tree frog is physically identical to another species of tree frog called Cope’s gray tree frog (H. chrysoscelis). The two species are almost impossible to tell apart in the field except for some differences in their calls. Examination of their chromosomes, though, not only distinguishes each species but also suggests an interesting evolutionary story. Cope’s gray tree frog is diploid (two sets of chromosomes) while the eastern gray tree frog is tetraploid (four set of chromosomes). It is thought that a common starting (diploid) species via a defective chromosome separation in embryonic development gave rise to cohorts of diploid and tetraploid individuals. These cohorts were separated by advancing ice sheets during the Pleistocene, and by the time the ice receded they had accumulated sufficient genetic differences to prevent their interbreeding.

I am not sure, then, whether I have eastern or Cope’s gray tree frogs around my house (or maybe both!).  Maybe I should spend some more time listening to their calls to see if I can distinguish the two species!

It is summer!! Enjoy!


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Signs of Summer 4: Interactions of Periodical Cicadas and Birds

Female cicada laying eggs. Photo by D. Sillman

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Science starts, as I have written before, with observation. You then have to filter through the sometimes bewildering array of events that you are observing and try to focus on those things that don’t quite make sense or on those things that seem to stick together. You can apply some creative thought (some imagination!) and begin to connect events with lines of cause or influence. You can then make explanatory models (or “hypotheses”) about/with these edited observations. These models are very satisfying and often incredibly elegant and beautiful! The critical thing about science, though, is the intellectual process doesn’t stop here. In science, we then challenge our precious hypotheses via experimentation and try to find their weak points. We try to show that our insight into Truth was, in fact, false!

Science, when it is working properly, is a very bruising ego-trip!

Which gets us, interestingly, to periodical cicadas and some of the bird species that we might expect to consume them!

A simple prediction about a periodical cicada outbreak year (year #13 or #17 in their life cycle depending on which cicada species or brood is involved) is that birds that can eat those cicadas should become quite abundant when their food supply is so dramatically increased! This predictive hypothesis seems so logical that it feels foolish to even test it!

American crow. Photo by D. Sillman

So, as the local periodical cicada outbreak raged on here in Apollo this spring, I was very surprised to observe that the numbers of cardinals, blue jays, crows, and grackles (all species that should be eating cicadas) in and around my yard, field and woodlot had plummeted!

Over the past 15 years I have regularly had 20 to 30 northern cardinals in the area immediately  around my house. They nest in my cedar and spruce and maple trees and, usually, each mating pair will have three clutches in a spring/summer. They wean their fledglings at my sunflower seed feeders over a multiple days long ritual of wing fluttering and begging and parental attention and then abandonment. This year, though, I have seen only 1 or 2 pair of cardinals and just saw my first fledgling a few days ago! Also the crows and blue jays that have regularly greeted me in the morning to receive their daily allotment of peanuts in the shell have been quiet this summer. Many peanuts dumped in my front yard in the morning sit untouched by birds (but, eventually, they get gathered up by squirrels!). And, the grackles just are nowhere to be seen!

This has been an odd spring/summer for birds in Apollo!

Cicada damage on a black locust branch. Photo by D. Sillman

Walter Koenig, a scientist at The Cornell Laboratory of Ornithology, has made a number of observations on bird species during cicada-emergence years. Koenig looked at the North American Breeding Bird Survey (a comprehensive survey of North American bird species that has been conducted every year since 1966) to see if he could find any evidence of possible correlations of the periodical cicada outbreaks with the fluctuating population densities of 24 species of potential periodical cicada predators. His analysis indicated that fifteen of these bird species had statistically significant population changes related to the cicada life cycle.

Cuckoos (Coccyzus spp.) were found in high numbers only during a periodical cicada outbreak year.  Red‐bellied woodpeckers (Melanerpes carolinus), blue jays (Cyanocitta cristata), common grackles (Quiscalus quiscula), and brown‐headed cowbirds (Molothrus ater), on the other hand, were found in higher densities for 1 to 3 years after a cicada emergence). These data fit the “expected” (or “logical”) model of stimulation of predator species when prey becomes increasingly abundant. Other potential cicada predators, though, responded very differently to the periodical cicada feast.  Red‐headed woodpeckers (Melanerpes erythrocephalus), American crows (Corvus brachyrynchos), tufted titmice (Baeolophus bicolor),

Blue jay. Photo by D. Sillman

Tufted titmouse. Photo by D. Daniels, Wikimedia Commons

gray catbirds (Dumetella carolinensis), and brown thrashers (Toxostoma rufum) were found in very low numbers during a cicada outbreak year. Their population densities declined when the cicadas were available but then increased back to “normal” the year after the outbreak and then for several years remained at their “normal” densities. Wood thrushes (Hylocichla mustelina) and northern mockingbirds (Mimus polyglottos) both had significantly reduced populations 1 to 2 years before the cicada outbreak but then returned to “normal” numbers during the outbreak and in the years after. Northern cardinals (Cardinalis cardinalis), and house sparrows (Passer domesticus) had significantly increased populations 1 to 2 years before the cicada outbreak followed by a return to “normal” population densities during the outbreak and in the subsequent years of the cicada life cycle.

Further, even though all of these bird species have inherently and distinctively fluctuating population densities , most of the potential cicada predators reached the lowest population numbers of their cycles the very year that the periodical cicadas were expected to emerge. These emerging cicadas, then, were preyed upon by a much smaller predator community than average! A very big advantage for the cicadas!

The classical description for the evolutionary selection of periodical cicada mass emergence and their very long subterranean nymph stage existence is predator saturation, and, subsequently, increased survival of reproducing adults. There seems to be another dimension to this strategy, though, that involves coordinating the long-term density fluctuation patterns of the cicadas’ main predators to the duration of the cicadas’ life cycle!

Koenig also looked at the data collected in the Audubon Society’s “Christmas Bird Count,” and found, six months before any adult cicadas might be emerging, reduced numbers of crows, blue jays and several other potential cicada-eating species. The decline, then, in these birds was something that was occurring long before there were any actual adult cicadas in the ecosystem!

Cicada exoskeletons after emergence. Photo by D. Sillman

A  question that has been historically asked is, “why do the cicadas have cycles of 13 or 17 years?” Why are these two prime numbers uniquely used in these spectacularly extended life cycles? Cicadas that abnormally emerge at years other than 13 or 17 years are almost all consumed by predators, and these populations tend to go extinct. Further, computer simulations in which cicada emergence was programmed to occur in a variety of even numbered years also resulted in the local extinction of the hypothetical broods.

Why are years 13 and 17 so important? The more mathematical among us point to the fact that they are both prime numbers (but, the purely mathematical explanation seems to end there). The more mystical among us might contend that 13 and 17 have innate, hidden powers and meaning on other planes of reality. The most logical scientific explanation that I have heard was from Walter Koenig himself in an interview with Discover magazine in June 2013: “ … something really cool (is) going on that we just don’t know about yet.”

Cicada damage on black locust trees. Photo by D. Sillman

Possibly, the infusion of such a bounty of food energy in the cicada mass emergence acts as a controlling force on the fluctuating populations of the potential cicada predators that leads inevitably to the predators’ population density nadirs just when the periodical cicadas are programmed to emerge! Possibly the maturing cicada nymphs underground are altering their ecosystems’ productivity as they get larger and feed more aggressively on their sustaining tree roots which then causes potential predator populations to decrease.

As Koenig and Andrew Liebhold wrote in their July 2005 paper in Ecology (Ecological Society of America):

“These results suggest that the pulses of resources available at 13‐ or 17‐year intervals when periodical cicadas emerge have significant demographic effects on key avian predators, mostly during or immediately after emergence, but in some cases apparently years following emergence events.”

So, as scientists what is next? We have an elegant and very intriguing hypothesis: the mass emergence of cicadas is controlling their potential predator densities 13 or 17 years into the future! Natural selection has zeroed in on 13 and 17 years not because they are prime numbers or have mystical meanings, but because they match the period frequencies of the birds’ population fluctuations! Hypotheses, though, are meant to be attacked and taken apart. Stay tuned for more updates (sometime in the next 17 years)!




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Signs of Summer 3: Cavity Nesting Team (Year 5)!

Photo by D. Sillman

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Over the past five years I have written a number of articles and posts about our Cavity Nesting Team study up at Harrison Hills Park in northern Allegheny County. This year we have twenty-nine nesting boxes scattered across the park, and the Team started our 2019 monitoring on March 30. We have built up a steady accumulation of observations and hypotheses during the years of our study. Our findings from 2015 helped us better understand the optimal location variables for our nesting boxes (and our relocated 2016 boxes were almost all utilized for nests!). Our 2016 data helped us design two experiments for 2017 in which we tried to regulate house wren nesting in our boxes (house wrens are very destructive to nesting bluebirds and tree swallows). The results of our experiments in 2017 were not very successful but we re-tuned some of our 2017 ideas for the 2018 season and achieved a sustainable equilibrium between bluebirds, tree swallows and house wrens.

Blue bird eggs. Photo by C. Urick

In 2018 we observed a record number of bluebird nests (23 nests) but also had a record number of bluebird nests that had no eggs (six) and ones that had a high degree (50% or more) of egg mortality (also six). The impacts of the eggless nests and the large number of lost or undeveloped eggs reduced the overall egg production for the season to the second lowest total of the previous four years (only 67 eggs) and reduced the total number of bluebird fledges to the lowest number we have observed over the four years of our study (46). Also, the early Summer “success rate” for our the bluebird eggs (percentage of eggs that fully developed into fledges) was the lowest we have observed in our study (63%).

Why did we see an apparent breakdown in the nesting and fledging success of our bluebirds? The weather last summer was very different from any of the previous years. We had record high temperatures in May (average daily temperature in May was seven degree F above historical averages) and extremely high rainfall in the months of April (148% over historical average), June (193% over historical average) and August (152% over historical average). We are not sure if these unusual weather conditions contributed to increased activity of nest parasites or predators or if they might have directly stressed either the adult birds or the nestlings.

This year’s Cavity Nesting Team consists of 17 volunteers: Deborah and I and Sharon Svitek take turns monitoring the boxes in and around the “High Meadow.” Dave and Kathy Brooke and Lisa Kolodziejski check the boxes around the “Bat House Meadow.”  Dave Rizzo and Megan Concannon and Marianne Neal take turns monitoring the boxes in the fields near the Environmental Learning Center, and Paul Dudek and Donna Tolk check the boxes at the park entrance and around the soccer fields in the southern end of the park. The boxes around the “south” pond are checked by Maureen and Dave Sagrati and David and Kielie Ciuchtas, and Patrick and Mardelle Kopnicky serve as resource people to help the new volunteers get adjusted to the program and to remind the rest of us about our working models and past observations. Data from our observations are uploaded to an on-line Google spreadsheet, and each week I summarize and distribute the accumulating data to all the members of the team.

Tree swallow. K. Thomas, Public Domain

Native cavity nesting bird species (eastern bluebirds, tree swallows, house wrens, Carolina wrens, titmice, chickadees, nuthatches, etc.) naturally use tree holes for their nesting sites. These holes are most often found in older, often dead or dying trees, and they are typically abandoned cavities that have been chiseled out by woodpeckers. The lack of the these older trees in most forests has led to a “housing crisis” for these cavity nesting species. Nest boxes, of course, are artificial substitutes for these natural tree holes.

So what have we seen so far this year?

Photo by D. Sillman

We saw our first two blue bird nests on March 29: one in a nesting box near the park’s Environmental Learning Center and the other in the High Meadow in the northern section of the park. These ‘first nests” of 2019 were seen three weeks earlier than the “first nest” of 2018! The first 2019 eggs were seen on April 12 (16 days earlier than the “first eggs” of 2018). By mid-April we had 8 bluebird nests scattered throughout the park and 20 eggs. By the end of May this first cycle of bluebird nesting and reproduction had generated 10 nests, 38 eggs, 33 nestlings, and 33 fledglings. A second wave of bluebird nesting then began around the first of June. Nine new nests were build in previously unused boxes (31 eggs, 3 nestlings so far), and four new nests were built in previously used bluebird boxes (20 eggs and 5 nestlings so far).

We have observed, then, a very robust production of eggs by bluebirds (89 eggs so far) and a very high rate of success of the transitions of egg-to-nestlings and nestlings-to-fledglings. In previous years the second nesting cycle of the bluebirds did not happen until mid to late July! We may see this year, then a third nesting cycle of these bluebirds.  The 89 observed eggs already exceeds the largest seasonal egg total from any of our previous study years (83 eggs were observed in the 2016 season)!

Tree swallow nests. Photo by T. Schweitzer, Flickr

Coincident with the second bluebird nesting, tree swallows also began building nests in our nesting boxes. In all of our previous nest box observation seasons tree swallows did not start their nest building until mid to late-June. The swallows, then are, like the bluebirds, on an accelerated time table in 2019 (3 to 4 weeks ahead of all previous years). We had seven tree swallow nests built by late May, and only one of these nests was in the south part of the park (near the pond).

In 2015, all three nesting boxes near the pond had had tree swallow nests, and we considered these boxes to be optimal for swallows because of the proximity of abundant flying insects (dragonflies etc.) over and around the pond. Only one box (Box V here in 2019)  of these pond-area nesting boxes has subsequently been used by tree swallows! We are still uncertain why the swallows are avoiding these seemingly optimal nesting sites! We speculate that the vegetative structure of the pond has changed over the years making it less desirable for tree swallow use or making it less productive for the aquatic insects upon which they preferentially feed.

A total of 35 eggs were observed in these seven tree swallow nests and 27 nestlings. Nest predators, however, raided two of the nestling-inhabited nests up in the Bat House Meadow and ate 10 nestlings during the first week of June. Of the 17 remaining nestlings, 3 have fledged and 14 are still in their nests.

House wren. Photo by dfraulder, Wikimedia Commons

Our strategy to control house wrens and reduce their impacts (egg and nestling destruction) on bluebird and tree swallow nests was developed during the 2017 and 2018 monitoring season. Male house wrens make “dummy nests” as part of their mating displays. Our strategy was to remove these partial nests whenever we came across them and thus keep the wrens in a constant state of display rather than actual reproduction. The 34 house wren eggs of 2016 and 2017 were reduced to 13 in 2018 (and total number of house wren fledges went from 23 in 2016 to 4 in 2018). Thus far this year there has been only one successful house wren nest (6 eggs) but all 6 eggs failed to hatch.

We had another house sparrow nest this year. The nest (and its 3 eggs), though, were destroyed by our nest box monitors. House sparrows are an extremely destructive, alien-invasive species. Their nests and eggs are not protected by the Migratory Bird Act, and their destruction was more than justified.

Why are the bluebird and tree swallow nesting cycles starting so much earlier this year? Why are the bluebirds and the tree swallows producing such  large numbers of eggs? Could it have something to do with the spectacular, local emergence of the periodical cicadas? Both bluebirds and tree swallows feed their nestlings invertebrate prey that is much smaller than the robust periodical cicadas. I have not seen any tree swallows catching and eating cicadas and none of the Team members have seen a bluebird eating a cicada. Possibly, though, the cicadas are having an indirect impact on the abundance of the smaller prey. Bluebirds (according to Benedict Pinkowski in his March 1978 Wilson Bulletin paper) primarily feed their nestlings butterfly and moth adults and larvae, grasshoppers, crickets, beetles and earthworms, and tree swallows (according to the Cornell Laboratory of Ornithology and the Tree Swallow Project) primarily feed their nestlings flies, leafhoppers, ants, wasps, bees, beetles and, when available, dragonflies. Could these prey items be more abundant if other competing avian predators are feeding on cicadas?

Next week: unexpected interactions of periodical cicadas and birds!!



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Signs of Summer 2: Three “First Birds”

Photo by Rasmussen (Wikimedia Commons)

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I tried to keep a close eye on the arrival of the spring migrating birds this year. I thank all of the people who sent me emails about their “first bird” sightings this year, too! Here are our first three “early birds.”


Photo by D. Sillman


Robins are still the archetypal harbingers of spring even though many of us, especially if we live near a habitat that has a suitable, winter robin-food supply (berries and other wild and domesticated fruits), have robins all year-round. Holly thickets, crab apple groves, wild grape arbors and dense shrub lands of raspberry, honeysuckle, poison ivy and barberry can all locally sustain flocks of over-wintering robins.

The robins that do migrate may move into nearby, food-rich habitats, or they may fly down to the southern U.S. states or into Mexico or, possibly, all the way down into Guatemala. They can also overwinter on several of the islands of Caribbean.

Prior to European colonization of North America, robins were neither as abundant as they are today nor as widely distributed. The opening of the Midwest and the Plains of the United States to farming coincidentally introduced European earthworms (the classic food for robins!) to these rich soils and have allowed robins to greatly expand their distribution and population numbers all across North America.

Here in Western Pennsylvania the return of the migrating robins comes in waves. This year (2019) robins were seen in some apple trees in New Kensington on February 28 but they did not get north into the Apollo area until March 21. Back in the 1990’s and 2000’s migrating robins arrived in Apollo like clockwork on either February 14 or 15. These mid-February dates corresponded to the yearly, brief, mid-February warm spells that have not occurred in recent years. In 2014 robins were first seen in Apollo on March 13 and in 2018 on March 1.  Their arrival is very soil temperature related: they fly in and begin hunting and consuming earthworms. After a winter of fruit, those worms must be delicious!

Photo by D. Sillman

Common grackles:

The arrival of the grackles are, for me, a very important sign of spring! Back in the 1990’s during our severe bouts with gypsy moths, common grackles were the only local bird that I saw eating gypsy moth larvae! The grackles would fly up to my spruce trees, grab gypsy moth caterpillars, take them out to the street and beat them on the asphalt until most of their irritating hairs were removed. They then would gobble them down! A small flock of grackles spent long hours working my trees. Ever since I have put out shelled corn for them in the spring as thanks.

Many grackles spend the winter in large, mixed-species flocks with red-winged blackbirds, brown headed cowbirds and starlings. Flocks numbering in the hundreds of thousands to millions of birds are seen in agricultural fields and marshlands in the south-central and southeastern United States. Some grackles, though, overwinter quite nearby (in sheltered spots in southern Ohio and West Virginia) in much smaller flocks. These “local migrators” typically are the first grackles to show up in the spring and the last to leave in the fall.

The arrival of the grackles is not a subtle event. Suddenly, one morning there will be a dozen grackles on the ground under my bird feeders gleaning the spilled seed. I then go out and spread some shelled corn, and the grackles with all of their posturing and “sky pointing” to assert their respective levels of dominance in their flock hierarchy spend many hours eating the corn and sunflower seeds often after dunking them in the water of the bird bath. When the grackles are here, I need to change the birdbath water every day!

Many people speak unkindly of grackles. They call them “unloved” and “dirty” and “noisy.” They are significant agricultural pests, and, in spite of the protections for most native birds under the Migratory Bird Act, they are frequently targeted for legal, mass extermination by farmers. Farms are the reasons that grackle populations grew so significantly along with the human populations all across the eastern and mid-western United States. Grackles probably were not a very abundant North America bird species prior to European colonization but reached a population peak of 190 million birds in 1974 due to the large number of farms and available grains. They have been declining, though, by 2% or so each year ever since. Their tendency to form large, roosting groups makes them particularly vulnerable to lethal population control measures, and the loss of suitable farm habitats and the reforestation of abandoned farmlands  have contributed to their significant decline (61% total decline since 1974: current population 73 million birds).

Here in Western Pennsylvania the grackles have consistently returned from their over-wintering sites in March: March 2 and 8 in 2017 and 2018, March 15 and 16 in 2014 and 2019, and March 25 in 2011, and they almost always bring red-winged blackbirds and the brown-headed cowbirds along with them.

Photo by Pixabay


Killdeer arrive in Western Pennsylvania with a great deal of noise and frenetic activity. They are the most widely distributed plover in North America and can live in both seaside habitats and also inland grasslands, farmlands, golf courses, parking lots, and even the flat graveled roofs of buildings. Often the first killdeer we see in the spring is either a male who is staking out the roof of the Engineering Building at Penn State New Kensington for his breeding ground or some other male that has chosen a nearby, flat-roofed grocery store for his future nesting site.  Killdeer are found throughout North America, Central America, the islands of the Caribbean, and into the northern portions of South America as far south as southern Peru. They migrate out of their northernmost ranges in the fall but are year-round residents in the southern United States and in the remainder of their warm-temperate and tropical distributions.  Migrating killdeer often seek out coastal habitats (beaches and dunes) and nearby agricultural fields for their overwintering sites.

Killdeer return to their northern breeding ranges in late winter or early spring. Their arrival in mid-March or early April is often the first appearance of a seasonal migrant, although here in Western Pennsylvania usually the robins and grackles (and the grackle entourage) have gotten here first. From 1998 to 2006, killdeer returned to the Nature Trail on the Penn State New Kensington Campus in the second week of March. They frequently faced very cold and even snowy weather for the next three to four weeks but persevered and found food and shelter. More recently, killdeer have returned to the Apollo area (about 15 miles east of the campus) on March 14 (2019), March 29 (2018), March 30 (2011) and April 16 (2014). This past year Patrick over in Fawn Township (about 16 miles north and west of Apollo) saw a killdeer on March 7!

The loud, screaming cry of the killdeer is a song which announces the eventual possibility of spring’s arrival if not its exact presence. Males along with their later arriving females carry out elaborate, soil scrapping behaviors (and duets of loud calling) within the breeding territory. One of these scrape sites will become the chosen nest site.  The nest is a scrape consisting of a 5 to 7 inch diameter shallow concavity in the soil or rocky substrate. It may be completely unadorned and unmodified by the bird, or it may have a few added rocks around its edges or bits of plant material laid upon it.

Killdeer lay on average four eggs in the nest (their clutches range from 2 to 6 eggs). The eggs are a very neutral buff color with a spattering of  black blotches that greatly enhance their camouflaged appearance. The eggs are very difficult to see even when you know the precise location of the nest! Both male and female incubate the eggs. The long, 28 day incubation period allows the chicks to undergo quite advanced development prior to hatching. The newborn chicks are fully feathered and are able within an hour or so of hatching to run, leave the nest, and even begin foraging for their own food. The parental birds guard the chicks but take no role in their direct care or feeding. The parents may, in fact, begin their second brood when the first set of eggs hatch. The parents then alternate between roles of incubators and chick protectors until the second clutch hatches.

Killdeer are very tolerant of humans and can live and reproduce in a wide range of human-modified habitats. Their population, like those of robins and grackles, has increased with the increased human presence in North America. Recent habitat destruction, though, and the impacts of herbicides and pesticides, farm and construction machinery, lawnmowers, cars, and trucks have significantly reduced killdeer numbers (47% reduction from 1966 to 2012). Several experts, however, contend that there are still more killdeer in North America now than there were before European colonization!

So these are, typically, the first three summer birds of our spring! All three are tied into human activity and are extremely tolerant of the presence of humans. All three, in spite of some recent declines, are quite possibly more abundant now than they were before European colonization of North America. They are also very welcome signs of spring and summer and help to lift us out of the cold and quiet of winter!







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Signs of Summer 1: Fireflies!

Photo by M. Lewinski, FLickr

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Several weeks ago Patrick over in Fawn Township noticed the first fireflies (also called “lightning bugs”) drifting about in his yard. Shortly after that, while taking our dog Izzy for her nightly walk, Deborah noticed that our field was glowing with clouds of blinking fireflies. Fireflies are the stuff of childhood summers and warm, July nights! I spent many nighttime hours with a Mason jar and lid in hand chasing down reluctant fireflies! It looks like this will be a good season for these interesting insects.

Photo by T. Arthur, Flickr

“Fireflies,” though, are not really flies at all (nor are they “bugs”). They are beetles in the family Lampyridae that along with several hundred other closely related “firefly” species (and also a number of protists, bacteria, fungi and marine invertebrate species) have the remarkable ability, in all of their life stages, to biologically generate light. The adult beetle, which is the form most familiar to people, is ½ to ¾ inch in length, with a flattened body that is predominately black in color with yellow highlights and prominent red spots on the back of its thorax. It has large eyes and long antennae and flies in a gentle, hovering manner. The light generating parts of these adults are in the terminal segments of their abdomens. The adult firefly has long, curved mandibles that suggest a predaceous life style, but only a few species have been shown to actually consume anything other than flower nectar or pollen during the very short adult portion of their life cycle. The less well known larvae of the firefly, called “glow worms,” live in leaf litter and are voracious predators. They eat other insects, mites, earthworms, and even slugs and snails.

The lights of the fireflies are communication mechanisms. The female fireflies, which are predominantly sessile, perch on the vegetation in its habitat and generate a species specific sequence of light flashes that attract the much more mobile males. The males respond with an answering light sequence and zero in on the females in order to mate. A few species of firefly have been shown to mimic the light sequences of other species in order to draw unsuspecting males to waiting, predaceous females. These females not only gain energy from consuming the males of these other species but also can accumulate chemicals from their prey which help to protect them from their own predators. This behavior is called “aggressive mimicry.”

Photo by Pixabay

After mating in the late summer, the females lay their eggs one at a time on the surfaces of woody or leafy debris. The eggs hatch in a few weeks and the emerging larvae enter the soil/litter habitat where they actively feed on a wide range of invertebrates. In late fall, the larvae burrow into the soil or under the bark of woody stems where they overwinter in an inactive, hibernating, state. In the spring, they re-emerge and continue to actively feed on their diverse array of prey species. After a few weeks, they re-enter the soil and pupate. They then emerge from their pupal chambers in early to mid-summer as adult fireflies. Abundant leaf litter and abundant moisture are needed for these firefly larvae to thrive!

The mechanism for the production of light in fireflies is mediated by the enzyme “luciferase.” High energy phosphates generated from food molecules are coupled via luciferase to the direct production of photons of light. Oxygen and magnesium are also needed  for this reaction to proceed. This coupling is extremely efficient (90%+) and generates almost no waste energy (heat) (compare this efficiency to a typical incandescent light bulb which is only 10% efficient (90% of applied energy is lost as heat!)).  The genes that regulate this light generation have been used in cancer research to mark and track metastasizing cancerous cells, and to also to monitor bacterial and viral infections, measure  gene expression, signal transductions and the movement and distribution of proteins and other macromolecules within a cell.

Photo by John B. Wikimedia Commons

There have been many reports of declining numbers of fireflies throughout North America. The widespread use of pesticides and herbicides, the loss of the leaf litter habitat required by larval life stages especially in suburban areas, and climate change driven drought have all been proposed as factors in the decline of the firefly. Also the prevalence of artificial lights in many of our human-modified ecosystems makes the light communication systems of the mating processes of the fireflies less efficient and may be responsible for a significant percentage of the decline in these beetles.

The firefly community in the Allegheny Forest is one of the richest and most diverse in the world! Fifteen species of firefly including the rare “synchronous firefly” (Photinus carolinus) can be found within the boundaries of the forest! One of these fifteen species, is the official state insect of Pennsylvania: the Pennsylvania firefly (Photuris pennsylvanicus).

A late June festival up near Tionesta, Pennsylvania was established to celebrate the Allegheny Forest firefly community. The festival is now in its seventh year and will be held on June 22 from noon to midnight at the Black Caddis Ranch B & B in Kellettville, 15 miles east of Tionesta on Route 666.

So get out and watch, chase, catch (and release) some fireflies! It’s what summer is all about!

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Signs of Spring 14: Yosemite (California, Part 3)

Photo by D. Sillman

(Click here if you would like to listen to an audio version of this blog!)

Yosemite Valley is located on the western slopes of the Sierra Nevada mountains of California. It is a tight walled, U-shaped space that contains some of the most impressive alpine scenery in the world. Most tourists enter Yosemite Valley after a long drive on roads that hug steep hillsides (with very few guard rails!). Last summer’s massive wildfires have blackened many of these down-slope and up-slope vistas (photo below). Then the road goes through a tunnel that is cut through the granite of one of the western-edging mountains, and then, suddenly, you are in the valley. The tunnel is quite beautiful in itself! Its granite walls and ceiling have been left exposed and their reflective, heterogeneous mineral crystals glitter in the headlights of the passing cars.

Burn areas in Yosemite N. P. Photo by L. Kalbers

Outside the tunnel is a small parking area logically named “Tunnel View” from which most of the landmarks and the sights of the valley can be seen. Even on the days with very light traffic (which are few and far between in this extremely popular destination) the small parking area is usually full requiring a drive further down the road to find a roadside parking spot often several hundred yards away.

Our choice in coming to Yosemite in the third week of May was guided by several considerations: 1. We hoped that there would be fewer other tourists here in the week before Memorial Day, 2. The weather should be dry and relatively warm so that we would be able to hike (historical weather data culled from the records at The Weather Underground predicted low 70’s F for highs and low 40’s F for lows with “0”inches of expected rain), 3. The melt of the winter’s snow from the high, surrounding mountains, should fill Yosemite’s famous waterfalls to their maximum, and 4. The early wildflowers should be riotously abundant in the high meadows!

Photo by D. Sillman

The actual weather for our days in Yosemite, though, was a little bit different than we expected. The temperatures were only slightly cooler, but each day had a 40% chance of rain! An “unusual” weather front had come into the mountains from the Pacific Ocean (it is hard, though, to call any weather pattern in these days of climate change “unusual!”) and dumped several inches of cold rain on us during our Yosemite stay. The rain clouds, at times, enshrouded the great, granite domes of the park making very dramatic impressions and photographs, but they also made the rocky trails quite slippery. These clouds and showers, though, kept the crowds away (or confined them to the tourist centers and coffee shops!) and gave us a much more individual Yosemite experience than we would have thought possible even in this week before the start of summer season.

So cloaked in ponchos and rain jackets with warm layers underneath, we struck off into the park! The waterfalls, by the way, were spectacular!! Our first short walk was out to Bridal Veil Falls just down the road from Tunnel View. The water flow was so massive there that a “soak zone” extended out more than 50 meters from the actual falls. Everyone who tried to walk out to see the falls got drenched!

Photo by L. Kalbers

Later that day we walked to the Lower Yosemite Falls. It is a much larger, but much more “civilized” waterfall! We could stand near the lower cascade and be surrounded by its incredible roar but not be pummeled by sheets of icy water! The drop of the three segments of Yosemite Falls covers just over 2400 feet making it the highest waterfall in North America. It was hypnotically impressive and was also an easily seen landmark and reference point from many places in the park.

The Sierra Nevada are very young mountains. They are made up primarily of a mass of granite that formed deep in the Earth some 100 million years ago. This granitic mass began to rise and tilt about 10 million years ago forming the mountain range. The uneven tilt of this rock generated sheer cliffs and high rock faces to the east and the relatively gradual set of rising elevations to the west.

View of Yosemite Valley from Glacier Point. Photo by L. Kalbers

The rising granite pushed up through the overlying, sedimentary rock. This rock overburden, unlike the granite, was quite erodible and through action of wind, water, ice and snow, was steadily ground away to reveal the surface of tough granite. Great cracks (called “joints”) formed in the rising granite. Some of these joints were vertically oriented and some were horizontal, but others were arching and rounded. These rounded cracks formed the curving surfaces of the granite domes that dominate the Yosemite landscape. These domes are only very slowly eroding, and, because of their surface geometries and the impacts of rain, ice and snow, they are constantly scoured of accumulating mineral debris. Soils do readily form on these granite domes and they stand, predominately uncloaked by vegetation!

Yosemite Valley was repeatedly carved by glaciers during the Ice Ages of the Pleistocene. The U-shape of the valley is distinctively a product of glacial sculpting. John Muir first proposed the glacier theory for the valley’s origin and used the still forming glacier valleys in Alaska as models to support his theories. Muir extensively described and studied the glaciers of Yosemite and, eventually, after a long acrimonious debate with formally trained geologists, his theories prevailed. There are still some glaciers in Yosemite lurking in the shady, north facing slopes of the mountains,  but 75% of the glaciers that John Muir studied are gone due to the ongoing warming trends of Climate Change.

Photo by D. Sillman

In our days at Yosemite we hiked around the western loop of valley floor and walked right up to the base of El Capitan. Two climbers were working their way up the sheer face of the mountain the morning we were there. We watched them with a mixture of envy and dread. A group of us also climbed the long, steep, rocky steps up to Vernal Falls in a light, steady rain, while others explored the Merced River and the trail to Mirror Lake. We also walked around the giant sequoia grove at Mariposa and the wet meadow of Wawona and were finally able to drive up Glacier Point Road (after the newly fallen snow had melted sufficiently) to go to Glacier Point (the site of the famous photo of Theodore Roosevelt and John Muir) and take in the dizzying overview of the entire valley. Snow still blocked many areas of the park, but everything we saw was incredible!

Snow plant. Photo by D. Sillman

And, finally, I want to talk about an aspect of Yosemite that is much less visible to most visitors than the great rock masses or waterfalls. Yosemite National Park (which contains Yosemite Valley) is a protected refuge for an amazing number of plants and also a good number of animals. California has the greatest biodiversity among the 50 states. It has 7000 plant species and 20% of these are found within the boundaries of the Sierra Nevada and Yosemite. Two hundred of these plant species are, in fact, found nowhere else in the world! We were a bit early for the blooming of many of the Yosemite species, but we did see a rich array of beautiful plants (Deborah identified 30 of them!) including snow plant (pictured above), Indian paintbrush, Brewer’s lupine, California poppy and smoothstem blazing star.

Western fence lizard. Photo by D. Sillman

We also saw some common animals and tried to find a few uncommon ones. Mule deer, chipmunks and ground squirrels made up most of our mammal sightings (although we did see one coyote). We didn’t see any black bears or big horned sheep. We saw no snakes but did encounter a fence lizard up on the rocks of Glacier Point (picture to the left)! Of the 150 species of birds that have been reported from the park, we only saw eleven. The most abundant were ravens and robins but the western tanager, spotted towhee and acorn woodpecker were wonderful, although, fleeting sights!

The animal I really wanted to see, though was the endangered, Yosemite toad (Amaxyrus canorus (formerly Bufo canorus)). At times we were up in the right altitude zone for these toads (6389 to 11,302 feet) but the snows had not sufficiently melted to shake the toads from their winter hibernation or generate their breeding pools. Maybe another week or two, and they would have been active.  The unusual color dimorphism of the male and female Yosemite toads (males are a uniform yellow-green to greenish-brown while females are dorsally black and covered with distinctive copper-colored blotches that have white-cream borders) reflect two remarkable gender-specific, natural selection matrices for these extremely high altitude dwelling amphibians. Also the common name for this species (the “tip-toe toad”) describes a particular evolutionary derived mode of locomotion that allows them to walk across snow fields without dragging their bodies on the cold snow surface! They would have been a wonderful creature to see!

Yosemite was an incredible place to visit. I can’t believe that it has taken me so many decades to finally get out there, but it was worth the wait! I am glad that we went when the weather was not ideal, too. It gave us the opportunity to see the park with just the right number of fellow human beings.






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