Signs of Summer 12: This Year’s Deer

Photo by D. Sillman

Photo by D. Sillman

White-tailed deer are both a charismatic species of our eastern forests and a major problem. The sight of a deer emerging from a stand of trees or brush is breathtakingly beautiful, but the damage they do to tree seedlings and forest understory plants (not to mention gardens, shrubs and ornamentals) is devastating. Some foresters, in fact, refer to white-tailed deer as “tree locusts,” and forest ecologists worry that the consequences of deer browsing on tree seedlings might include the disruption of forest succession and renewal throughout the northeast! Fern-lands and moor-lands could possibly replace our diverse hardwood forests if deer consume the next successional generation of trees!

Photo by N. Tonelll, Flickr

Photo by N. Tonelll, Flickr

In many of our state parks and game lands there are enclosures designed to prevent white-tail deer from browsing on tree seedlings and other understory plants. These “deer exclosures” have fences 8 or 10 feet tall, and the areas that they protect are typically filled with densely growing understory plants and large numbers of tree seedlings and saplings. The forest outside the fence barrier, though, often has a cleaned out, park-like appearance that is referred to as a “deer savannah” (see picture to the left). The impact of the deer is terribly clear! The deer are consuming tree seedlings and also many of the other ecologically important plants of the forest understory.

In 1900 it was estimated that there were only 500,000 white-tailed deer left in North America. Intense hunting pressures and massive deforestation through the Nineteenth Century had decimated their numbers and made them a species only rarely seen in our forests. The sighting of a deer, in fact, could make front page news in some of the rural newspapers of northwestern Pennsylvania! Today, however, there are estimated to be over 15,000,000 white-tailed deer in North America! Forest regeneration, elimination of natural predators, and strict hunting laws have allowed this species to reach population numbers and densities that far exceed those even of the pre-European settlement forest ecosystems!

Photo by Penn State

Photo by Penn State

A three year study conducted at the Penn State Deer Research Center (State College, PA) was recently published in the journal Biological Invasions. This paper examined the interactions between native and invasive plants and deer. In particular, the study was designed to determine which types of seven native and eight exotic plants were eaten by white-tailed deer.    The plants were grown in containers that were then placed into a deer enclosure containing eight mature does. Cameras equipped with motion detectors monitored and recorded deer feeding behaviors, and at the end of the study period the amount of each plant that was consumed was determined.

Four plants were avoided by the deer. Three of these were exotic invasives (garlic mustard (Alliaria petiolata), Japanese barberry (Berberis thunbergii) and Japanese stiltgrass (Microstegium vimineum)), and one was a native (but frequently invasive) species (hay-scented fern (Dennstaedtia punctilobula)). All four of these plants are common invasives in our deer infested forests! This study clearly showed that their abundance in these ecosystems is due to their not being consumed by deer. Selective browsing by deer is contributing to the persistence and spread of these invasive plants!

Deborah and I noticed on our Baker Trail hikes six years ago that many native plants were avoided by deer in favor of introduced ornamental and garden species. We planted a native perennial garden in our field in an attempt to have some deer resistant flowering plants around our house. We especially planted bee balm (Monarda spp) and enjoyed its bright blossoms and the wonderful array of bees and hummingbirds it attracted! The “deer resistance” worked for about a year, but then the deer decimated all of the previously resistant species (especially the bee balm!). Deer are adaptable (and voracious!). We now hide the bee balm in our fenced-in yard!

Photo by B. Lammers, Wikimedia Commons

Photo by B. Lammers, Wikimedia Commons

A recent article in the New York Times (by James Gorman, July 18, 20166) discussed another aspect of the large, eastern U.S. white-tailed deer population: collisions with cars. Each year there are more the one million deer/car encounters, and two hundred people a year die as a result!  Gorman’s article highlights some serious discussions among wildlife biologists (in the journal Conservation Letters) about a way to reduce deer populations and the subsequent number and staggering costs of deer/vehicle accidents. These wildlife biologists estimate that over thirty years the change that they have proposed could prevent 155 human deaths and 21,400 human injuries, and save $2.3 billion! The change is quite simple: re-introduce the eastern cougar to its original range throughout the East! These researchers estimate that a cougar would kill 259 deer over its six year life span, and that allowing cougars to return to their historical population densities would help to bring the exploding deer populations under control!

Of course there are a few downsides to having a large, active predator among us. Livestock would be attacked and eaten (estimated losses 2.35 million dollars a year), people would be attacked and even killed (estimated only one person per year would die of cougar inflicted injuries), and house pets would also be consumed by the cougars (the researchers, though, could not come up with a realistic estimate of the numbers of dogs and cats that would be eaten by the cougars). The researchers also acknowledged that the fear of being in a car crash doesn’t generate the same level of anxiety in most people as the possibility of being leaped upon by a lurking cougar.  They recognize that their plan has a steep uphill climb to reach any level of public acceptance!

There is also the distinct possibility that adding cougars to the eastern U.S. fauna might not affect deer populations at all! The wildlife biologists acknowledge that 75% of the deer killed by cougars would probably have died due to some other fatal event, and that more fawns would be expected to be born if the number of adults were reduced. So, total deer population numbers might stay the same!

I don’t expect cougars to be widely re-introduced into our eastern forests. We do need, though, to be aware of the seriousness of our current deer problem! We can’t fence in a whole forest to prevent the browser hijacking of its natural regrowth and succession, but we need to find a way to find a new, functional balance to maintain our forest biomes!

Photo by D. Sillman

Photo by D. Sillman

Just a short note about the deer in my yard and field: we have, as I have written about many times before, a herd of deer that numbers 7 or 8 individuals. This year there are two older and three younger does (probably last year’s fawns) and two fawns. For the first time in six years, there are no twin fawns. The two older does have each had a single offspring. There is also a young buck that tries to join this loose group out. He is sporting short, simple looking antlers and may be the male sibling of one of the younger, yearling does. The fawns are very interested in the buck (see photo above!), and we have watched them approach him to sniff and even touch noses. Usually, though, the does chase the young buck away if he tries to get too close or too familiar.

Photo by D. Sillman

Photo by D. Sillman

The big attraction, right now, for the deer are the green apples that are falling from the trees in our orchard! The fawns especially like the sour, hard apples and are out under the old trees at almost any time during the day. There must be something incredibly addictive in the taste of these apples! Twisted up faces and violent head shaking while chewing them doesn’t seem to deter any of them from taking a second (and third, and fourth!) bite!

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Signs of Summer 11: Trees, Mastodons and Giant Ground Sloths

Photo by D. Sillman

Photo by D. Sillman

I was trimming low branches under my Norway spruce a few days ago, making room for some leftover stones from my driveway wall re-construction, when I found a white oak seedling growing along with some struggling Virginia creeper and poison ivy. The seedling looked quite healthy in the cool, moist, but almost sunless space under the spruce, and since, at least until very recently,  there have been no white oaks growing on my property, I assumed that this seedling’s acorn was flown in a few years ago and accidentally dropped by a blue jay or crow.

Reproducing oak trees invest a substantial amount of their metabolic energy into their acorns. They make their acorn “packages” as appealing as possible to a wide range of birds and mammals and count on some acorn consumers being clumsy with these nutritious morsels. A few of the acorns will, hopefully, be dropped in places where germination is possible and where seedling browsers aren’t abundant. I was looking at the winner of an intense reproduction gauntlet: an oak seedling growing far from the parental tree.

In a nutshell (sorry, very bad pun!) that’s why plants have evolved fruit and nuts! Inside these tempting pieces of food are the embryos of the plants’ next generation, and those plants that can use animals to fly or walk at least some of these embryos to more distant habitats will disperse, thrive and then go on to produce more and then even more individuals. They will be more likely to “win” the great biological contest of survival and replication!

Photo by fir0002, Wikimedia Commons

Photo by fir0002, Wikimedia Commons

There are examples of this process all over my yard and field: there are chestnut seedlings growing in several corners of my two acres where squirrels, carrying the nuts dropped them (or buried them) and then went off to do something else. I have watched gray squirrels carrying chestnuts that are still encased in their spiky burrs suddenly stop, shake their heads and fling the nut away. My sense is that one of the burr spikes jabbed itself into the flesh of the squirrel and triggered the reflexive shudder and toss! Could the sharp spikes of these burrs be more than just protective barriers against non-dexterous nut predators? Maybe they are dispersal triggers, too? The latter might even be more important in an evolutionary scheme!

Fruit is designed to attract consumers at just the right time so that the mature plant seeds can go for a ride often inside of the fruit consumer’s intestines. The seeds then leave the consumer along with a dollop of fertilizer (feces has many uses!), and, if all of the environmental variables line up, the seeds germinate, grow, survive and then also reproduce. I look around my yard and see raspberry thickets, mulberry trees, grape vines, cherry seedlings, and poison ivy growing in perfusion all thanks to the bird dispersal of each species edible and enticing fruit!

So, fruits are made to be eaten (seed and all) and the payoff for the plant, as I have said before, is the sudden acquisition of wings and legs!

There are a few apparent glitches in this scheme, though. There are quite a few plants (especially some trees) that have fruits that either can’t be eaten or seeds within their fruit that would, quite literally choke a horse. A seed that can’t be swallowed will be very hard to disperse! The plant’s investment into that fruit and seed, then, does not result in the big dispersal payoff (it more closely resembles the investments that I have in my retirement portfolio!).

Photo by Haplonn, Wikimedia Commons

Photo by Haplonn, Wikimedia Commons

Dan Janzen (University of Pennsylvania) is a renowned tropical ecologist (and the author of the 1983 book Costa Rica Natural History which I have enjoyed and relied on as an authoritative reference for the past thirty years).  Many years ago Janzen noticed that a middle canopy tree of the rain forest of Costa Rica called the “pink shower tree” (or Cassia grandis) had long, woody seed pods that were not eaten by any of the native animals of Costa Rica. These seed pods, though, were avidly consumed by cattle and horses (both of which were alien exotic species in these ecosystems!). He eventually described about forty other tree species of these forests that produced fruits that were not eaten by any of the native animals! Unconsumed fruit meant non-dispersed seeds! The evolutionary “fruit and seed dispersal contract” was not being honored in today’s ecosystems!

Giant ground sloth, Photo by Ballista, Wikimedia Commons

Giant ground sloth, Photo by Ballista, Wikimedia Commons

Janzen in collaboration with Paul Martin of the University of Arizona developed the idea of “ecological anachronisms.” The Costa Rican trees must have developed their fruits in co-evolutionary relationships with large animals that had since gone extinct!  These trees without their giant ground sloths or massive, elephant-like gomphotheres now were investing their precious metabolic energy into a seed disposal system that no longer existed! They had become “ecological anachronisms.”

A tree that grows closer to home that also reflects a hidden evolutionary history is the Osage orange (Maclura pomifera). The fruit of the Osage orange is a large, seed-filled, softball sized sphere that contains a white, sticky fluid. No animal eats these fruit and, not surprisingly, the Osage orange has a very restricted natural range (in east-central Texas,

Osage orange fruit, B. Martin, Wikimedia Commons

Osage orange fruit, B. Martin, Wikimedia Commons

southeastern Oklahoma, and northwestern Arkansas) even though it is very well adapted to grow throughout the continental United States and southern Canada (it has been planted, often as a living fence, in 39 of the lower 48 states!). This natural range restriction is undoubtedly due to the absence of natural seed disperses (probably mammoths or giant ground sloths, two species that went extinct in the later Pleistocene when, coincidentally or not, humans first came to the North American continent).

Kentucky coffee bean fruit, Hardyplants, Public Domain

Kentucky coffee bean fruit, Hardyplants, Public Domain

There are many other temperate and tropical trees that have fruit and seeds that are anachronistic: the large seed pods of the Kentucky coffee bean tree and the honey locust (two trees that my students and I have planted in conjunction with the Pennsylvania “Tree Vitalize” program) are not eaten by native animals (and both tree species have very constricted natural ranges in spite of their robust ability  to grow under a wide variety of conditions (as demonstrated by their survival along the streets of New Kensington and many other towns in Western Pennsylvania!)). Avocados, as Lee Drake pointed out last March in Albuquerque, look like giant ground sloth or mastodon food to me! So do papayas, pawpaws, persimmons, and even wild squash! Big fruit and seeds require big mouths and big intestines to be ecologically and evolutionarily functional!

Photo by Dantheman, Wikimedia Commons

Photo by Dantheman, Wikimedia Commons

There are many features of our trees and forests that reflect other ecological anachronisms and relationships with departed species. Whit Brounaugh wrote a wonderful article entitled “The Trees That Miss the Mammoths” in the Winter 2010 issue of American Forests, and George Monbiot wrote “Thinking Like an Elephant” in the June 2015 issue of BBC Wildlife. Growth patterns of trees, the strength of their trunks and branches, the patterns and sizes of their protective thorns, etc. all suggest a long, adaptive evolutionary interaction between the trees and large browsers and seed dispersers that no longer exist.

Many of our trees have been sculpted by evolutionary and ecological ghosts, and the momentum of these evolutionary changes has continued even long after these “prime movers” were gone!

 

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Signs of Summer 10: Eastern Towhee

Photo by D. Sillman

Photo by D. Sillman

Eastern towhees (Pipilo erythrophthalmus ) are one of Deborah’s and my favorite birds of summer. We met our first towhee in 1984 out on the old farm we rented in northern Allegheny County. A pair of them set up their nesting territory in the woody thickets that bordered the long, rutted, gravel path that was our only way in and out of the hollow where our farm house and barn were situated. We frequently walked down the path to get to the hiking trails and pipeline cuts that ran up into the wooded ridges to our south and whenever we did we were chirped and chittered at by the flashing male towhee. Initially we had to go to our Peterson Field Guide to figure out that he was, as they were called then, a rufous-sided towhee. They were on the same page as the rose-breasted grosbeak which was just after the page with the blue grosbeaks and the indigo buntings, three birds that we also had the great pleasure of seeing on the farm that summer. It was a wonderful place for birds!

At first I thought the towhee, in spite of its obvious field guide location among the sparrows, was some sort of robin or related thrush. It was smaller than a robin but so much larger than a sparrow that it really took some intellectual discipline to accept the kind of bird that they were! Their beaks, once you got a good look at them, were obviously cone-shaped and very non-thrush-like, but it made me glad to see later on as I read about them that they are frequently called “ground robins” (which, if you think about it, is a very strange name! I mean what should you then call regular robins that are mostly found on the ground?).

Photo by D. Sillman

Photo by D. Sillman

Towhees are birds of thickets and edges. They build their cup-shaped nests on the ground under the protective cover of dense branches and vines and frequently dig the nest down into the covering leaf litter for better concealment. They typically feed in the surrounding leaf litter, too, using a two footed scratching technique to fling the dry leaves about to uncover a wide variety of insects and other invertebrates. In fact, one of the best ways to find a towhee out in the field is to listen for loud, energetic scratching under the bushes!

Towhees also eat a wide range of seeds and fruits and have even been known to consume small lizards and snakes! They also have been observed raiding the nests of other birds to eat eggs and nestlings, but, hey, no species is perfect, right?

Towhees are subject to intense nest parasitism by brown headed cow birds (Molothrus ater). In some areas over half of the eastern towhee nests will have cowbird eggs. The towhees, though, do not seem to able to recognize these foreign eggs and spend a great deal of their reproductive energies feeding and rearing these brood parasites.

Eastern towhees in their northern ranges migrate relatively short distances either between sheltered local habitats or milder, southern regions. They have relatively short wings and are not strong fliers. They dart about from ground to low shrub branches in a very characteristic flapping and gliding flying pattern.

Photo by D. Sillman

Photo by D. Sillman

We regularly see eastern towhees up at Harrison Hills Park when we are out doing our bluebird nest box monitoring. The extensive shrubby areas in the park are ideal for this species, and we are frequently hear both the underbrush scrapping and scratching and also the distinctive “cherrit!” (often sounded out in field guides as “drink your teeeeee!”) of the very territorial males.  The males seem especially interested in us as we walk past or through their territories. They keep a close eye on us and shadow us along our way.

Interestingly, eastern towhees mark out much larger territories than they actually require in order to provide adequate food supplies for their nestlings. They are extremely aggressive against any other towhee that might venture into their territories and have a wide range of displays and postures (frequently involving the flashing of the white tips of their wings) by which they express their anger and outrage! Not surprisingly, towhees are very solitary birds and seldom seen in flocks, but there is a marvelous name for these seldom seen aggregations! A group of towhees is called a “tangle” or a “teapot” of towhees.

Photo by J. Mayer, Flickr

Photo by J. Mayer, Flickr

Towhees can nest two or sometimes even three times in a season. A parental pair stays together for a given spring or summer but then the mating pairs re-shuffle for the next season. The female builds the nest with only minimal assistance from the male. It takes her about five days to complete the nest (a complex mix of sticks, rootlets, grass, bark, and leaves, and lined with soft grass and animal hair (paper and other human materials may even be incorporated into the nest materials).

Two to six creamy white, brown spotted eggs are laid in each clutch. As previously mentioned, nest parasitism by brown headed cowbirds is very high and overall nest predation by chipmunks, raccoons, and a variety of snakes is also quite severe. Nest success rates of less than 20% have been regularly reported. The Cornell Laboratory of Ornithology reports that there are approximately 28 million eastern towhees in North America and that their population has declined by 49% between 1966 and 2015. Loss of brushy habitats (due to human development of sites and also to ongoing forest succession) and the impacts of cowbird parasitism are given as the main causes of these population declines.

I am very happy to report that for the second summer in a row Deborah and I have a towhee residing in our yard! We see him regularly at our front yard bird feeder and also under our arbor vitae and spruce trees digging through the leaf litter. For the past three years I have raked my autumn leaves under these shrubs and trees to give shelter to insects and to generate a food source for foraging birds (not to mention possible overwintering habitat for tree frogs!). Maybe these leaves are the key to drawing towhees in close to our house! They are a truly welcome addition to our local fauna!

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Signs of Summer 9: Summer Signs

Photo by D. Sillman

Photo by D. Sillman

Deborah and I have been keeping our eyes on some of the biological and ecological “events” of the summer of 2016. Since we have just slipped past the halfway point of the season, it’s time to think about some of these.

We have had some very successful reproductive efforts by the birds that visit our feeders and leaf piles! The cardinals and the robins have each had two nesting and fledgling cycles so far and seem to be starting up on another (both are out gathering new beaks-full of grasses and stems for their nests!). The chickadees and titmice have also gotten two nesting cycles done but seem to be less inclined than the cardinals or the robins to start into a third. The Carolina wrens also went through their usual mate re-shuffling kerfuffle in late June and have settled into a second nesting period.

Photo by D. Sillman

Photo by D. Sillman

The common grackles arrived at our feeders late in the spring, but they must have nested and fledged their young very quickly because there is now a robust flock coming to the feeders dominated by a large percentage of dark brown, immature birds. They swoop into the feeder areas about 10 am and especially like the scattered shelled corn (which they frequently dunk in the water of the bird bath before eating!).  I am very tolerant of the grackles and put out extra corn for them at mid-day. I remember them voraciously eating gypsy moth caterpillars back in the gypsy moth explosion years of the 1990’s and want to continue to thank them for their efforts!

Photo by D. Sillman

Photo by D. Sillman

The blue jays and crows have completed their single nesting efforts and are now leading their fledglings around our complex habitats drilling them on food finding protocols and safety procedures. The first and second robin fledglings have gone from stumbling klutzes tripping through the leaf piles to confident, elegant hunters and efficient spearers of worms and caterpillars.

The mourning doves seem as though they have been mating all summer! I have lost track of how many nesting cycles they have gone through! The sharp-shinned hawks mated back in the late winter (the female was, as usual, extremely loud calling from the bare branches of our backyard black locust tree). Early in the morning we frequently see a sharp-shin swooping across the top of the front yard bird feeders. We also frequently find small piles of feathers (usually doves or cardinals) around the edges of our field. We have never seen, though, a sharp-shin fledgling! They are said to be secretive birds during reproduction and very wary of larger hawk predators (like goshawks and red-tails).

So, most of the birds seem to be behaving quite normally for a Western Pennsylvania summer, but many of the insects and other arthropods are acting quite oddly this year and they may be having some impacts on a wide variety of other species!

Aedes albopictus Photo by J. Gathany CDC Wikimedia Commons

Aedes albopictus Photo by J. Gathany CDC Wikimedia Commons

For example (and we are not complaining about this at all!), we have fewer mosquitoes around our house this summer. We are regularly sitting out on our deck well into the evening with minimal aggravation from buzzing and biting mosquitoes. These longer deck times, though, possibly go along with seeing fewer chimney swifts and fewer bats soaring over our field gobbling up all sorts of flying insects (but especially great numbers of mosquitoes!). The hummingbirds also came into our yard quite late this summer (they waited until the lure of the flowering bee balm in Deborah’s flower bed was overwhelming!). Hummingbirds are frequently described as “nectar powered insect eaters.” Possibly the lower numbers of mosquitoes reduced the feeding quality of our yard and field for the hummingbirds and caused them to linger elsewhere until the nectar scents were just too compelling!

Photo by JJ Harrison Wikimedia Commons

Photo by JJ Harrison Wikimedia Commons

Also, and we are not complaining about this either, there were no little “sugar ants” in the kitchen this spring! Every other May and June that we have been in this house (and in one week we will celebrate the 27th anniversary of our house closing!) we have had several weeks, at least, of columns of ants streaming in through tiny cracks around the kitchen window and door in search of any available crumbs or sticky residues. This year the ants did not show up! We think that these ants are mostly odorous house ants (Tapinoma sessile), but they may have been joined in bumper ant years, by the European exotic species called the pavement ant (Tetramorium caespitum).  They are both little black ants that may fall into the very broad, common category of “sugar ant,” but one of them (“odorum”) gives off a bad smell when it is crushed.  We seldom crushed any of them, but frequently washed a number of them down the drain.

Another insect change this year is a very small number of brown marmorated stink bugs (Halyomorpha halys ) emerging from their winter, in-house hibernations.  Again, we have no problems with the direction of this change! I talked about this earlier this summer (Signs of Summer #3, June 16 2016). The lower numbers may be due to the growing activity of the predators of stink bug adults and eggs. Everything from spiders and chickadees to earwigs and katydids are now eating these exotic pests.

Photo by D. Sillman

Photo by D. Sillman

And finally, another arthropod that is less numerous and less active in our summer of 2016 ecosystems is the deer tick! We have had, along with most of Pennsylvania and much of the northeast, huge numbers of deer ticks in our rural and suburban ecosystems. These ticks are the arthropod vectors that spread the bacterium that causes Lyme disease, and as a consequence of their large numbers, Pennsylvania has had for the past few years the greatest number of Lyme disease cases in the country. Our yard and field have been a rich reservoir of these ticks. Walking out in the yard in sandals almost guaranteed you a tick or two, and our dog, Izzy, and our cat, Mazie, weekly (and sometimes daily!) picked up deer ticks from their forays within the fenced-in yard off of our deck. This spring and summer, though, we have found no deer ticks on either humans or pets! Further, our trampling around at Harrison Hills Park to check our bluebird houses also has not generated any ticks (a big change from last year!).

I am not sure why, and would like to ask everyone reading this post to think about your tick experiences this summer. Have you seen any deer ticks as a consequence of hiking or yard work or dog/cat interactions? Are we seeing some change in our deer tick populations?

Wow! Pennsylvania will surely get crowded with people if we start to have mosquito free and tick free summers! Real estate prices will go up! House sales will increase! Nothing but good things (unless you like chimney swifts and bats, of course).

More on all of this soon! Happy summer, everyone!

 

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Signs of Summer 8: Cavity Nesting Team!

Photo by D. Sillman

Photo by D. Sillman

Last year I wrote two blogs about our Cavity Nesting Team study up at Harrison Hills Park in northern Allegheny County (May 28 and October 29). We had a very good year with our bluebirds and tree swallows. We had 13 boxes that had bluebird nests with a total of 65 eggs and 48 fledglings (a 74% survival rate), and we had 9 boxes that had tree swallow nests and a total of 31 eggs and 22 fledglings (a 71% survival rate). Nine of our thirty nest boxes, though, did not have any nesting activity, so, using our locations of utilized boxes as a guide, we relocated seven of these inactive boxes to try to make them more attractive to cavity nesting bird species. We left two of the inactive boxes in their 2015 locations because they seemed to be in ideal spots for cavity nesting birds (we must acknowledge, however, that we were wrong about their ideal locations! (see discussion below)). Our overall criteria for relocation were quite straightforward: boxes too close together tended not have nests (so spread out the clumped together boxes) and boxes right on the edges of field (i.e. very close to surrounding woodlands) were not used (so move the boxes away from the extreme edges of our fields).

This year’s Cavity Nesting Team consists of eight volunteers: Deborah and I and Sharon Svitek take turns monitoring the boxes in and around the “High Meadow” area of the park. Patrick and Mardelle Kopnicky check the boxes around the “Bat House Meadow.” Chris Urik and Odessa Garlitz take turns monitoring the boxes at the park entrance and up in the field near the Environmental Learning Center, and Paul Dudek checks the boxes around the pond and soccer fields in the southern end of the park. Every box is checked each week, and then each observer enters their data into an on-line Google spreadsheet. Each week, Deborah compiles and distributes the growing data tables to each member of the team. Chris Urik also has made GPS maps of the park showing the precise location of each nesting box.

Photo by D. Sillman

Photo by D. Sillman

As I talked about last year, 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 typically found in older, often dead trees and are frequently abandoned cavities that have been chiseled out by woodpeckers. Any site management plan that favors woodpeckers (allowing dead trees to remain in the forest and not managing the forest or manipulating it into an even aged stand) will favor cavity nesting bird species.

Nest boxes are artificial substitutes for these natural tree holes. Eastern bluebirds, in particular, came under a great deal of stress in the past century. The influx of the alien invasive English sparrows and European starlings along with the habitat spread of the nest parasite, the brown headed cowbird, were major reasons for the bluebird’s numerical and distributional decline throughout the twentieth century. Human destruction of nesting and feeding habitats also contributed to this decline. Human efforts to provide existing bluebird populations with suitable and secure nesting sites (“bluebird boxes”) have, however, been extremely successful in bringing this beautiful species back from the brink of possible extinction. The North American Breeding Bird Survey reports that since 1966 eastern bluebird populations have increased by nearly two percent a year! The Cornell Laboratory of Ornithology estimates the worldwide population of eastern bluebirds (80% of which spend at least some time in the United States) at a very robust 22 million individuals.

K. Thomas, Public Domain

K. Thomas, Public Domain

We are just past the halfway point of the summer, but our nest box data is showing some very interesting trends. First and foremost, our strategy for moving the inactive nest boxes has been very successful. All seven boxes that we moved have had nesting activity this spring and summer! Five of them have had bluebird nests (and have generated 13 bluebird fledglings), one box had a successful chickadee nest (4 fledglings), and one had a tree swallow nest (with eggs, nestlings and fledglings that were too hidden in the nest materials to count). Further, four of these nests were then utilized by house wrens (although it seems these secondary nests did not produce any viable fledglings). The two inactive boxes from 2015 that we did not move (because they just seemed like PERFECTLY located boxes!) still did not have any nesting activity. We need to look at these two locations more closely to try to see why they were not utilized by any of our cavity nesting species! We need to learn to think more like bluebirds and swallows!

So far this summer 17 of our boxes have had bluebird nests (with 61 eggs and 45 fledglings). These numbers are almost equal to the totals from all of last year, and we are just coming into the second wave of the bluebird nesting and reproduction! We expect to significantly surpass last year’s egg and fledgling totals for bluebirds!

K. Thomas, Public Domain

Tree swallow, K. Thomas, Public Domain

Our tree swallow numbers, though, have been less robust than last year. Only six boxes have had tree swallow nests and there have been only 9 confirmed fledglings (although two nests did have nestlings that we expected did fledge, but the nest construction prevented direct observation of the birds. Even so, the 9 fledglings (even plus the 6 or 7 that might have come from the concealed nests) is well below the 22 fledglings we observed in 2015. Tree swallows have been described as “income” breeders that base their timing of reproduction on

Photo by dfaulder, Wikimedia Commons

House wren, Photo by dfaulder, Wikimedia Commons

short-term rates of food intake near the time of breeding. Reduced clutch size in tree swallows is a strategic response to limited resource abundance. Since the primary food of nestlings are adult insects that have aquatic larvae possibly some factors (weather? water quality? something else? ) have reduced the abundance of these insects and the tree swallows have responded by curtailing reproduction. It is also possible that the increased abundance and nesting activity of the house wrens has affected the tree swallow nesting and reproduction efforts. House wrens are known to actively interfere with the nest box selection and nesting activity of tree swallows.

So the cavity nesting cycle continues! We will keep monitoring these boxes on through Labor Day. I will let you know our final counts and observations!

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Signs of Summer 7: Watching Crows

Photo by D. Sillman

Photo by D. Sillman

The American crow (Corvus brachyrhynchos) is a large, loud and obvious avian species that inhabits a wide variety of habitats throughout Western Pennsylvania.  They were recently featured on the cover of the March/April 2016 issue of Audubon magazine (the bird equivalent, I am sure, of a musician being on the cover of Rolling Stone!). The articles in this issue focused on a number of studies that evaluated the intelligence and individual and communal memories of crows.

For example, John Marzluff at the University of Washington in Seattle went out in the 1990’s and caught and banded (and then released) a cohort of crows. Marzluff and his banding team wore “caveman” masks while they were netting and banding the crows. Subsequently, Marzluff and his team returned to the crow banding area and were ignored unless they wore their caveman masks (even Dick Cheney masks did not elicit a violent crow response!). Not only did the crows that had been directly captured and handled by the caveman scientists remember and react to the caveman masks, but also their fellow flock (or “murder” as a crow flock is called) members quickly learned the caveman face and joined in on the mobbing and commotion. Marluff’s team regularly returns to this crow territory and, although it has been over ten years since the initial trapping event and the originally trapped crows are now undoubtedly all dead and gone, the flock still responds in what the article labels a “crowpocalyspe” whenever the caveman masked researchers return.

Photo by D. Sillman

Photo by D. Sillman

These studies (along with some remarkable brain activity analyses using PET scanners and radioactive isotopes) not only show the individual crow to be extremely intelligent (Mazluff calls them “flying monkeys!”) but also highly connected within its flock to a communication and information system that has to be defined as a culture!

Crows are seldom seen alone. In the non-breeding part of the year (fall through the winter) they form large, communal flocks of hundreds to thousands of individuals. Increasingly these large, winter flocks can be found in urban areas (much to the distress of the area’s human residents!). Lancaster, PA, for example, had 20,000 overwintering crows in its Park City Mall a few years ago, and a number of towns in Pennsylvania have faced the loud (and messy) problem of large flocks of winter roosting, “urban” crows! The warmth and lights of the city environment and the protection it brings from great horned owls and other crow predators are thought to be some of the factors that are selecting for these urban-centered crows. During the breeding season (spring to late summer) crows form smaller, more cohesive, familial flocks, that break up into even smaller foraging groups that daily travel out across the countryside looking for food.

Photo by D. Sillman

Photo by D. Sillman

Communication between individuals in the foraging groups and within the larger flocks is a very important aspect of crow biology. The remarkable and extensively documented intelligence of crows (their ability to solve food-gathering problems, to learn to mimic human vocalizations, to employ a variety of complex strategies to gather food etc.) is thought to be a direct extension of their evolutionary success as a social, highly efficiently communicating species. Crows, by the way, have longer rearing and nurturing periods than other bird species. These “learning periods” are even longer than those observed in many mammals! These nurturing periods can last up to a year and a half and enable the parental generation to communicate extensive amounts of very functional survival information (hunting and foraging strategies and techniques, habitat selection preferences, etc.) to their offspring.

American crows can be found residing in or moving through a great variety of ecological habitats. They seem to prefer a broad functional range that includes both fields (for grasses and seeds and for small vertebrate and invertebrate prey species) and woodlands (for night roosts and for protection). Human agricultural systems are especially favored by the American crow. Their negative impacts on grain crops can be extensive. It is estimated that in the United States the American crow population numbers over three billion individuals! Many states (including Pennsylvania) allow hunting of crows to try to control their numbers.

Crows eat a great variety of foods. Invertebrates (like grasshoppers, grubs, earthworms, and caterpillars) are consumed as they become seasonally abundant. Vertebrates (bird eggs, small birds, rodents) are eaten opportunistically or may even be actively hunted. One spring, a few years ago, out in my side field, I observed a crow swooping down on a low flying female northern cardinal. The crow slammed down on the cardinal striking it with its chest and knocking it to the ground. The crow then landed next to the dazed, but still moving cardinal, picked it up in its beak, and flew off with it. Several other crows followed close behind, and the whole group was loudly pursued by five or six blue jays. I have in the past also observed crows picking off young red squirrels as they walked in line along a tree branch behind their parent.

Photo by D. Sillman

Photo by D. Sillman

Crows also eat carrion and are active scavengers of human garbage. Crows utilize their excellent vision to find and obtain their food. While hunting and feeding individuals of the flock take on specialized jobs (some functioning as lookouts, for example, while other members of the flock feed). Vocal communications between individuals of the flocks are critical to the overall success of the foraging group. Complex hunting behaviors have also been observed in crows. Some these include mobs of crows driving rabbits from a field across a roadway. A few of the driven rabbits were hit by cars and were then eaten by the crows. Crows have also been observed actively interfering with other predators (like river otters) to distract them from their captured prey which the crows then appropriate for their own consumption. These behaviors are further examples of the group dynamics and extreme intelligence of this remarkable species.

I have written before about “my” crows. There are three crows that wait for me each morning to come out and dump a couple of handfuls of peanuts under my bird feeders. They watch me from surrounding tree tops, excitedly caw when I carry out my bucket of birdseed, corn and peanuts to fill my feeders, and often swoop down to start picking up and swallowing as many peanuts as they can (as fast as they can) even before I get back to my front porch.

Crow populations have been increasing all around the world. Some researchers speculate that this incredibly adaptable and intelligent species is benefiting from the ongoing population declines in most of the more specialized avian species. The adaptable, generalist crow can occupy many niches in an ecosystem. We will undoubtedly be seeing a lot more of them in the coming years!

 

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Signs of Summer 6: More on Bees

Photo by I.Tsukuba, Flickr

Photo by I.Tsukuba, Flickr

I had an email from a friend a few weeks ago asking me about the impact of lawn mowing on bees. Since I regularly mow a one acre field that is a complex mix of grasses and flowering plants, I have had some experience adapting my mowing to the populations of bees (and other pollinators) that visit the flowers throughout the summer. I also wanted to check the literature to see if there had been any published papers about the impact of mowing on bees.

It is important to note that most people mowing suburban lawns won’t have any significant interaction with bees or other pollinators because their lawns are pollenational deserts. It’s a good news/bad news thing! The expanses of  single grass species that are so carefully and expensively manipulated into flat green carpets have no plant species that would attract (or feed and nurture) pollinating insects. So for any of you managing one of these ecological disaster zones, you don’t need to worry about your mower interacting with bees.

For people like me, though, who allow a rich mixture of grasses and “weeds” (and I use that word in its most non-pejorative sense possible!), there are times of abundant flowering (of dandelions, violets, clovers, and many other breathtakingly beautiful “weeds”) when bees and other pollinators might be out in the lawn. So the question is: is a mowing a recognized hazard for bees?

I poked around in the literature trying to find any studies that examined or quantified the impact of lawn mowing on bees. I could not find a single article. I did find, though, some recent, very comprehensive studies and compilation papers that described the collective matrix of stresses that are negatively impacting bees.  The figure below summarizes the 2013 findings of the OPERA Research Center of the Universita Cattolica del Sacro Cuore in association with the European Union:

bee impacts good versionLawn maintenance practices that generate small field sizes, monocultures of grasses, or that involve the utilization of broadly applied pesticides would definitely fit into the bee stress/impact matrix, but negative impacts of grass mowing practices don’t ever come up in the scientific discussion.

What do I do when mowing my mixed field of grasses and “weeds?” When the clover blooms I just don’t mow. I skip a week or two to let the bees have their fill of the clover nectar and pollen. The yard, the bees, the clover and the mower (me) are all benefited by a week or so off (there are many other things to do in the summer instead of mowing grass)! When I do mow and there are bees out and about on the scattered, flowering weeds, I go slow enough so that the bees (who are exquisitely sensitive to sounds, vibrations, and even electrical fields (see discussion below)) can get out of the way. I also keep my mowing blade quite high and often don’t even cut the clover flowers as I pass through the grass.

Photo Public Domain, Pixabay

Photo Public Domain, Pixabay

In summer the “field bees” that are out gathering pollen and nectar have very short life spans. Worker bees only live for about six weeks spending just the last half of their lives flying out of the hive to visit flowers. During the long weeks of the summer, then, there will be wave after wave of field bees heading out to find flower sources. On their flights they are exposed to potential predators, to sudden changes in environmental conditions, and to other physical dangers (including mowing). Fortunately, the robust reproduction of a healthy hive can keep the field bees coming!

So the answer to my friend concerned about lawn mowing and bees is: the overall impact is probably small and there are some simple things that the mower can do to reduce that impact even more.

There have been several other articles about bees over the past few months. A study by the United Nations’ Intergovernmental Science-Policy Platform on Biodiversity and Ecosystems Services published online back in March enumerated the potential economic cost of the worldwide decline in pollinators. This study stated that both vertebrate and invertebrate pollinators are needed for 35% of the global crop production that sustain human consumers. The value of these crops is estimated to be $577 billion per year, and many of these pollinating species (including birds, bats, and 20,000 species of bees) are facing significant population declines and even extinction.  Causes of these declines include the loss of wild plants and their essential nectar and pollen foods, exposure of of the pollinators to pesticides, and the rising levels and increasingly rapid word-wide distribution of pathogens and parasites. The OPERA study chart (above) summarizes the UN’s findings on pollinator stresses very well.

A team of researchers at Penn State just published a paper in the journal Atmospheric Environment describing the impact of air pollution on the the ability of honeybees to detect (and follow) scent molecules being generated by flowering plants. Rising levels of ozone greatly inhibited the chemical sensory systems of honeybees and led to longer, less efficient foraging and pollinating patterns!

Photo by B. Moisset, Wikimedia Commons

Photo by B. Moisset, Wikimedia Commons

In some happier research, a study published in June in the American Midland Naturalist examined the pollen types gathered by mason bees (Osmia species) around the Rocky Mountain Biological Laboratory in Colorado. A number of the mason bees studied specialized in gathering sunflower pollen from their surrounding vegetative habitats. Sunflower pollen, though, is very low in nutrient quality compared to other types of available pollen. The mason bees, though, that gathered the sunflower pollen had much lower levels of parasitic wasps affecting their larvae. There was a distinct, overall survival benefit, then, of reduced parasitism when the nutrient poor pollen was used nearly exclusively to fill the brood chambers and feed the mason bee larvae! Looking at bumblebees, though, another Penn State research group just published a paper in the Proceedings of the National Academy of Sciences in which they determined that these types of bees preferentially gather the highest nutritional quality of pollen from the flowering species in their habitats.

Photo by Trounce, Wikimedia Commons

Photo by Trounce, Wikimedia Commons

And finally, a study published at the end of May also in the Proceedings of the National Academy of Sciences demonstrated that bumblebees have specialized body hairs that sense electric fields! This type of an electrical sensory system is quite uncommon in terrestrial organisms, but may be used by bumblebees to find flowers or to avoid dangers (like lawn mowers perhaps?). The researchers also speculated that these electrical sensory hairs may be present on many type of insects and may explain some anecdotal observations of insect (especially pollinating insect!) disruptions in areas of human generated “electric smog” (i.e. locations with power lines, and dense concentrations of radio waves and wireless communication networks).

So, your cell phone may be affecting your honey bees, everyone! Keep your calls short!

Summer is racing past! I hope that everyone is out enjoying it!

 

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Signs of Summer 5: Jellyfish

Photo by R. Rezabek

Photo by R. Rezabek

Halifax Harbor (according to many (but not all) authorities) is the second largest natural harbor in the world. It is a beautiful place with lots of history and activity. We visited Halifax on the sixth day of our cruise, and Deborah and I had a wonderful time walking along the harbor boardwalk and looking at the boats and at the people. The photograph to the left was taken by my cousin, Randy Rezabek (who along with his wife, Charlene, was also on the cruise).  It shows a French Navy training sailing ship that had just been sailed across the Atlantic. We watched the crew go about their morning maintenance work on the ship. Then after a pause for a leisurely, group smoke, they all went for a long run down and around the harbor walkway. Only the French would warm up for a five K run by smoking a couple of cigarettes!

There was a nice crowd on the boardwalk and a number of friendly dogs to say hello to and pet. As I mentioned last week, though, there were no seagulls to speak of and the water of the harbor seemed unnaturally still and quiet. I later learned about Nova the hired Harris’s hawk (whom I mentioned last week). Nova served as a local gull assassin and deterrent, but he was not out and about as we walked around the harbor.

Photo by D. Sillman

Photo by D. Sillman

We did get to see something wonderful, though. Standing out on an extension of the boardwalk next to an art display of “melted” street lamps (you had to be there to appreciate it!), we looked down into the water and saw a large, reddish jellyfish (its “bell” was over a foot in diameter) go bobbling by (photo to the left).

There are four common jellyfish in Nova Scotia: the Arctic red jellyfish, the lion’s mane jellyfish, the constricted jellyfish, and the sea gooseberry. It is likely that the Arctic red and the lion’s mane jellyfish are the same species (the taxonomy of their genus (Cyanea) is very confused). So, seeing the size and the red color of this specimen led me quickly to assume it was a lion’s mane jellyfish (an organism that I have talked about in my introductory biology class for many years (more on that later!), but one that I had never seen before in the wild!).

Deborah and I watched the jellyfish for fifteen or twenty minutes (until it disappeared in the ripples and surface glare of the harbor water). No one else seemed to notice it floating by!

Cabbagehead jellyfish, Photo by K. Pepper

Cabbagehead jellyfish, Photo by K. Pepper

Jellyfish are among the oldest multicellular animals in nature. They have been found in fossils that date back almost seven hundred million years! “True” jellyfish (like the beauty we watched floating across Halifax Harbor) are members of the cnidarian class Scyphozoa. They are especially abundant in cold ocean habitats but can be found all over the world. During my high school years in Houston I spent as much time as possible down in Galveston Bay and along the Gulf coast. I remember seeing a particular jellyfish that we called a “cabbage head” (scientific name Stomolophus meleagris) rising and falling in the warm, sheltered waters of the bay. In places the water was densely packed with them! We also frequently had Portuguese Man-o-wars (Physalia physalis) wash up onto the beaches. The man-o-wars, though, are not true jellyfish. They are colonial assemblages of individuals of cnidarian class Hydrozoa. They still sting, though, and are close enough in form and function to be at least casually called “jellyfish.”

Jellyfish anatomy is very simple. They are made up of two layers of single cell thick tissues (one on the outside of the body and one lining the inside). In between these layers (and making up most of their body weight) is a non-cellular mass of gelled water called the “mesoglea.” The two tissue layers have specialized groups of cells that take on sensory functions, nerve-like functions, muscle-like functions, and digestive functions. They also have, especially concentrated on their dangling tentacles, cells called “cnidocytes” that can eject venom-ladened proteins called nematocysts that the jellyfish can use for hunting or for protection.

Lion's mane jellyfish, Photo by D. Hershman, Wikimedia Commons

Lion’s mane jellyfish, Photo by D. Hershman, Wikimedia Commons

The lion’s mane jellyfish (Cyanea capillata) is especially abundant in the cold waters of the North Atlantic and the North Pacific Oceans. It feeds on zooplankton, small fish, and smaller jellyfish. It in turn is preyed on by sea birds, large fish, and sea turtles (the leatherback sea turtle in eastern Canadian waters avidly feeds on lion’s mane jellyfish!). The lion’s mane jellyfish itself is also a very important hiding place for shrimp and many small species of fish. These vertebrate and invertebrate species live among the tentacles of the jellyfish and gain a significant degree of protection from other potential predators.

As I mentioned before, I have talked about Cyanea for many years in my introductory biology course at Penn State. I used it as a vivid example of Class Scyphozoa primarily because of its other common name: the giant jellyfish! In 1870 a specimen of Cynaea washed up on the shore of Massachusetts’s Bay that had a bell that was seven and a half feet in diameter and tentacles that were over one hundred and twenty feet long!   “Giant” is a very appropriate adjective for this species, indeed! I don’t know how long it took that specimen to grow to that size, or if there are other Cyanea of equal sizes out in their cold ocean habitats, but the growth potential of the “one footer” we saw in Halifax Harbor could be impressive!

There is evidence that jellyfish populations all around the world are increasing. Possibly over fishing has reduced jellyfish predator levels or human generated pollution (especially nutrient runoff into the oceans from agricultural fields) has generated conditions increasingly favorable to jellyfish growth and reproduction. Jellyfish, for example, thrive in nutrient-rich ocean waters that are low in oxygen, conditions that are being observed throughout our human-impacted ocean habitats. The large “blooms” of jellyfish can have serious economic impacts. Shoreline power plants have had their cooling water intakes clogged by excessively abundant jellyfish. Some plants have even had to shut power production until the jellyfish numbers could be reduced.

Dried jellyfish, Photo by Oleg, Flickr

Dried jellyfish, Photo by Oleg, Flickr

Amazingly, jellyfish are being actively fished for and processed as human food and are considered to be great delicacies in some Chinese, Japanese, and Korean cuisines! Some shrimp trawlers on the East and Gulf Coasts of North America can actually make more money trawling for jellyfish (especially that “cabbage head” jellyfish (also called the “cannonball jellyfish”) that I mentioned before!

I didn’t talk about jellyfish stings or the wild array of “cures” and treatments for the skin lesions caused by the venom in the nematocysts. I’ll save that for another blog! Just watch your step when you walk barefoot on the beach!

 

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Signs of Summer 4: The Curious Case of the Missing Gulls

MS Vandeem (Photo by D. Sillman)

MS Vandeem (Photo by D. Sillman)

From Arthur Conan Doyle’s Sherlock Holmes story “Silver Blaze:”

Gregory (Scotland Yard detective): “Is there any other point to which you would wish to draw my attention?”

Holmes: “To the curious incident of the dog in the night-time.”

Gregory: “The dog did nothing in the night-time.”

Holmes: “That was the curious incident.”

Halifax Harbor (Photo by D. Sillman)

Halifax Harbor (Photo by D. Sillman)

From the deck of the MS Vandeem cruising down the St. Lawrence River:

Fellow Cruiser: “Is there any other point to which you would wish to draw my attention?”

Me: “To the curious incident of the sea gulls.”

Fellow Cruiser: “But there are no sea gulls.”

Me: “That is the curious incident.”

In anticipating our cruise down the St. Lawrence I prepared myself for two ecological experiences: 1. I anticipated seeing great flocks of sea birds (especially sea gulls) all along the river and estuary, and 2. I anticipated seeing whales (13 species of whales (from belugas to blue whales) spend their springs and summers in the St. Lawrence River and Gulf!). Amazingly, though, there were almost no seagulls or other sea birds to be seen over the week of the cruise, and the only whale we observed was a harbor dolphin that Deborah spotted in Bar Harbor, Maine! The whales might have been avoiding the noise and fuss of our large cruise ship (The MS Vandeem), but sea gulls, based on my experiences along the Texas Gulf Coast and the Virginia mid-Atlantic coasts, should have been drawn to this boat and to the various port towns we stopped at like flies to a picnic!

Where were they?

Ring billed gull, Photo by D. Daniels Wikimedia Commons

Ring billed gull (Photo by D. Daniels Wikimedia Commons)

Background reading about the birds of eastern Canada listed four main sea gull species: the ring-billed gull (Larus delawarensis), the herring gull (L. argentatus), the great black-backed gull (L. marinus) and the black-legged kittiwake (Rissa tridactyla).  The great black-backed gull and the black-legged kittiwake are most frequently found to the north and to the seaward sides of the places we were scheduled to visit (they are true seas dwelling gulls, not, as my cousin Amy recently pointed out to me, bay dwelling “bagels!” (Happy retirement, Amy!)), so my expectation was that we would see quite a few ring-billed gulls (they were estimated to make up 80% of the gulls along the St. Lawrence) and herring gulls (estimated to make up 10% of the St. Lawrence gulls). In fact, the largest single breeding colony of ring-billed gulls was quite close to where we boarded the Vandeem just east of Montreal (on the Ile Deslauriers: a colony of 51,000 pairs of birds!). Unfortunately, we could not see this island from the deck of our boat!  We did see several great blue herons (Ardea herodias) flying over Montreal and down the St, Lawrence just before we boarded the Vandeem, but not many other birds at all!

Herring gull Photo by D. Daniels, Wikimedia Commons

Herring gull Photo by D. Daniels, Wikimedia Commons

Along the Quebec stretch of the St. Lawrence we saw a handful of herring gulls but no ring-billed gulls. When we docked at Quebec City, there were no waiting flocks of gulls of any kind to greet us as we disembarked from the boat. As we continued down the St. Lawrence from Quebec City and headed out into the Gulf of the St. Lawrence, we saw a few more herring gulls, a couple of ring-billed gulls, and a pair of common terns (Sterna hirundo). When we docked at Charlottetown, Prince Edward Island (or Sydney or Halifax, Nova Scotia) there were also no flocks of gulls, no great flying commotion greeting us on the docks.

In Charlottetown we sat out on a dockside table and had several baskets of steamed mussels and clams (and a very fine local ale). We watched two double crested cormorants (Phalacrocorax auritus) stand to dry themselves out on some old pilings in the harbor but were neither entertained nor pestered by any gulls. We had a similar experience on the waterfront boardwalk in Halifax (in Sydney it was far too cold and wet to sit outside! We did see, though, a pair of American black ducks (Anas rubripes) swimming around in a little cove near the dock).

Where were the sea gulls?

Herring gulls have been having a very tough time of it over the past fifty years. The Cornell Laboratory of Ornithology reports that their population has decline 3.5% each year since 1966. That percentage has compounded into an 83% total population decline over this time period! Changes in commercial fishing methods (less dumping of waste fish and refuse), a significant decline in total commercial fishing due to depleted fish populations, and greater control over landside waste disposal, waste dumps and landfills have all reduced the available food for this active, omnivorous scavenger. Further, oil and pesticide pollution and the loss of nesting sites have all had negative impacts on herring gulls. Also, herring gulls incubate their eggs in their huge nesting colonies for over a month, and their nestlings don’t fledge until they are six weeks old! This extended period of egg and nestling existence makes the herring gull quite vulnerable to nest predators (a list that even includes their fellow herring gulls!) and to deliberate human destruction of eggs!

There was an article in The Guardian (June 30, 2010) asking the question, “Why were there no seagulls in Charlottetown. PEI?” One answer came from a reader who reported that a friend of theirs had worked for the Royal Society for the Preservation of Birds (RSPB) back in the 1960’s systematically destroying seagull eggs in nearby PEI colonies (seagulls, according to the RSPB, needed to be destroyed because of their habits of eating the eggs and nestlings of other bird species!).

Harris's hawk (Photo by C. Delgada, Wikimedia Commons)

Harris’s hawk (Photo by C. Delgada, Wikimedia Commons)

Another article I found was published in 2014 on the CBC News web site. This article featured a Harris’s hawk named “Nova” that was hired (along with his handler) by the city of Halifax to patrol the harbor area of the city. The hawk actively killed seagulls and generated a predator presence that greatly reduced the local seagull population!

Deliberate human actions, then, seem to have been one factor in reducing the local presence of seagulls especially in places that wanted outdoor restaurants and harbor-side walkways for tourists (i.e. all of the places that the MS Vandeem took its travelers!).

Another factor that might have been impacting the number of sea gulls that we observed, though, might simply have been the timing of our visit. Both the herring gull and the ring-billed gull were right in the middle of their seasonal nesting periods. Possibly their colonies have been driven far enough away from the high human-use sites of our cruise ship itinerary that the birds were not able to make forays into these towns while still protecting their nests or feeding their nestlings. I like to think that in August the sea gull numbers in this visitation sites would improve. I would be happy to wear a broad-billed hat (and even put a cover over my glass of ale or basket of shellfish) when sitting out at a dockside table if it would mean an accompanying show and clatter of gulls!

 

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Signs of Summer 3: Stink Bugs!

Photo by D. Sillman

Photo by D. Sillman

As we have talked about before, the brown, marmorated stink bug (scientific name: Halyomorpha halys) is a native species of northeast Asia (Japan, Korea, and China) and has become over the past 20 years a serious invasive pest throughout the United States. It is thought that this insect was first released into the United States in Allentown, PA in 1996. It apparently traveled from northeast Asia in a shipping container that was delivered either to the port of Philadelphia or Elizabeth, New Jersey and then trucked to Allentown. Five years later this new, alien, invasive species was recognized and identified by entomologists at Cornell University, but by then large populations were being observed throughout eastern Pennsylvania, New Jersey and New York. This insect has now spread to forty states and is especially abundant in the eastern United States. It has very large populations in Pennsylvania, Maryland, Virginia, New York, New Jersey, Massachusetts, Delaware, Ohio, and North and South Carolina. Its spread to California and Oregon was allegedly via a car driven by a person traveling from Pennsylvania to California in 2005!

The ability of these stink bugs to overwinter is remarkable. There is some mortality among the hibernating bugs, but a significant percentage of them make it through to spring and to their opportunity to mate. A mated female is then able to lay up to three hundred eggs! The relative severity of the winter does, however, affect their percentage of survival. Several models of climate change and global warming have included increased survival of stink bugs at higher and higher latitudinal locations with, then, significantly larger spring and summer populations of this potentially destructive pest. Many of these stink bugs find their way into our houses and spend the winter months hibernating in tiny crevices and hideouts all around us. Their periodic emergence throughout the winter is our only reminder that they are close by!

Brown marmorated stink bugs feed on over one hundred and fifty plant species including a number of crops that are of great economic importance to humans. Fruit trees (especially apple and pear), soybeans, and peanuts are crops significantly damaged by these insects. I have also seen stink bugs in my yard feeding avidly on the grapes growing on my grape vine.

D. Lance Wikimedia Commons

D. Lance Wikimedia Commons

When these stink bugs first made their appearance here in Western Pennsylvania most potential predators were actively repelled by their pungent scent. Spiders, birds and almost every other type of possible insect eating invertebrate and vertebrate species actively avoided contact with the stink bugs, and, subsequently, their populations grew out of control. In the fall of 2013 and in the spring of 2014 we caught thousands of stink bugs in and around our house. We filled up dozens of one liter, plastic bottles with their carcasses! Over the past two years, though, we have not experienced these huge fall and spring outbreaks! This spring I have caught maybe twenty or thirty total stink bugs (I haven’t even filled one plastic bottle yet!). A far cry from the thousands of 2013 and 2014!

Photo by D. Sillman

Photo by D. Sillman

What has happened? It may be that predators are adapting to the noxious scents of the stunk bugs and are reducing their effective populations! We have observed spiders actively trapping and eating them. The picture Deborah took of this jumping spider chewing its way into the captured sink bug is a great visual of arthropod control! Birds (especially titmice and chickadees) regularly flare up to the window screens of my house and snag unwary stink bugs. They fly them over to nearby branches and gobble them down! (Go chickadees!)The predator guilds of our surrounding vertebrate and invertebrate communities have apparently adapted themselves to this new (and formerly incredibly abundant) food source! Control has been achieved, at least in the area immediately around my house!

A few months ago an old friend, Karen Shaver, sent me a link to an article about predators of brown marmorated stink bug eggs. The article (published in the journal Biological Control) was written by Rob Morrison (a research scientist at the USDA-ARS Appalachian Fruit Research Station in Kearneysville, WV). Morrison and his colleagues tested twenty-five potential arthropod predators of stink bug eggs and found several that voraciously devoured the egg masses. Katydids, crickets, ground beetles, jumping spiders and earwigs all actively ate the stink bug eggs (it is especially nice for me to see earwigs talked about in a positive manner! (See my essay about earwigs in my July 23, 2014 Signs of Summer #7 blog!)). Morrison’s group emphasized that modifying habitats to encourage the growth and abundance of these egg predators might be a very effective, long term way to control the populations of this potentially destructive crop pest!

So the brown marmorated stink bug is still with us, but it seems to be getting under control mostly through ecosystem adaptations to its presence and to its potential as prey and food for both vertebrate and invertebrate predators! Pesticides have not been terribly effective in preventing crop damage by stink bugs primarily because of their mobility (they hide in vegetation away from the treated field crops and then swoop in to feed thus limiting their exposure to the applied pesticides). The new observations of active predation of adult bugs and their eggs by an array of arthropod species might indicate that non-targeted destruction of crop dwelling arthropod predators via the pesticide treatments might actually make the stink bug infestation worse!

So, stink bugs are a relatively new and not terribly pleasant sign of summer for Western Pennsylvania. Fortunately, our surrounding biotic community is hard at work to keep them from being the ONLY sign of summer and fall that we notice!

 

 

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