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

Photo by D. Sillman

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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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Signs of Spring 13: Giant Trees (California, Part 2)!

Photo by D. Sillman

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We drove up from Fresno into Kings Canyon National Park on snow covered roads. The trees in the surrounding woods were frosted with fresh snow and there was a continuous, but not very deep snow pack on the ground in between tree trunks. It was a perfect Christmas setting even though it was May 20 and the start of our summer vacation!

We checked into the John Muir Lodge and then using a map provided by the lodge that looked curiously like a placemat, walked off to see the General Grant Grove of giant sequoia trees before dinner. It was cold and starting to snow again, but the distance looked negligible and we were very excited to see the giant trees!

Unfortunately the real map distance was about two miles to the grove from the lodge. The walk there was all downhill, too, which meant the walk back to the lodge restaurant and our all important dinner, was going to be an uphill slog probably in the cold, damp dark! Fortunately, about halfway down to the grove, my son-in-law, Lee, jogged back to get the car and met up with us at the grove.

Photo by D. Sillman

Giant sequoias (Sequoiadendron giganteum) are immense trees  with a long evolutionary lineage. Sequoia species were abundant back in the Mesozoic Era and were browsed upon by leaf-eating dinosaurs. One explanation for their great size, in fact, is based on a coevolutionary “arm’s race” with the long neck dinosaurs. The taller giant sequoias were increasingly selected for in ecosystems occupied by the longer and longer necked sauropods until, at last, the genetic tendency of these trees to grow to such staggering heights was firmly established in their lineage.

Climate change and especially the Pleistocene ice ages drove the descendant species of the sequoia line into more and more restricted habitats. Today, the giant sequoias are naturally found only in 75 separate groves within a 260 mile long and 15 mile wide area on the western slopes of the Sierra Nevada Mountains. They require a humid climate with both moderate rainfall (35 to 55 inches of rain/year) and dry summers. They also need a deep, moist, well drained, sandy-loam soil in order to thrive. The very large specimens of the giant sequoias need all of these site variables to be ideal in order to reach their maximum heights. The road down to the General Grant Grove followed the contours of a confined, topographic bowl within which soils would be deep and where water would readily accumulate.

Photo by D. Sillman

Giant sequoias, unlike their close relatives the coastal redwoods, are almost never found in pure stands. The giant trees are typically scattered out among sometimes very dense stands of California white fir, sugar pine, and incense cedar (at lower elevations) or red fir (at higher elevations). On slightly drier sites ponderosa pine and California black oak may also be added to the accompanying tree community. On sites where fire has been actively suppressed, there may also be a thick shrub layer along with a very dense growth of white firs surrounding the sequoias and their other attendant tree species. The General Grant Grove had abundant white fir, incense cedar and some scattered ponderosa pines in between the staggeringly large sequoias.

Seeds are produced in giant sequoias in trees as young as ten years, but trees 150 to 200 years old on into old age produce the most abundant cones and seeds. On average, a mature tree makes 1500 new cones each year. The trees, though, retain cones year after year and a given tree may actually have 10,000 to 20,000 cones attached to its branches. Some of these cones may be green or brown and seedless, but many will be viable seed cones.  Each seed cone can contain 200 seeds, so each tree represents a very large potential seed reserve. The giant sequoia seeds are light-weight and winged, so that they tend to fly some distance (up to a quarter of mile) away from the parental tree.

A sequoia seed has a germination rate between 20 and 40%, but once released from their cones, they have a very short time of viability primarily due to desiccation. Moisture is the key to germination, and seeds shed close to the time of snow melt typically have the best chance to sprout.

Photo by D. Sillman

Many of the currently existing giant sequoia groves are not sustainably reproducing (although we did see some sequoia seedlings in the General Grant Grove). These non-reproducing sequoias are referred to as “successful relics” in their fir and cedar and pine ecosystems. The reason for this thwarted reproduction lies in the extreme fastidiousness of the sequoia seeds and seedlings.  A seed falling on  thick ground surface litter or a grass cover will dry out too quickly to germinate. A seed falling under dense shrubs or under a low tree cover may germinate but the seedling will not be able to photosynthesize (the seedlings are very intolerant of shade). Given the current state of high density of shrubs and tree associates around the sequoias (primarily due to fire suppression), almost none of the shed seeds/seedlings survive.

Release of the seeds from the cones is stimulated by a variety of agents. Fire is possibly the most important force: the heating of the cones from a soil surface fire opens the cones and allows the seeds to fall on a , hopefully, well scoured and very receptive area of land. The chickaree (the Douglas squirrel) feeding on the cones also stimulates seed release as do the larvae of the long-horned wood boring beetle as they dig under the scales of the cones.

Photo by D. Sillman

It is interesting that although the giant sequoia is not reproducing well in its natural range, it does grow quite readily in many other places in the world. Deborah and I found a very tall (100 feet?) about two foot diameter (chest height) giant sequoia growing in the botanical gardens of the University of Basil in Switzerland! Many public and private gardens and arboreta all over the world have thriving giant sequoias gracing their treescapes!

There are many ways to use numbers to describe giant sequoias, but they all fail to prepare you for their epically immense sizes. The tallest giant sequoias is 310 feet, the biggest trunk diameter (at chest height) is 347 inches (almost 29 feet!), the oldest is 3200 years, and the most massive (the General Sherman tree down in Sequoia National Park) is 52,500 cubic feet in volume. The average giant sequoia is 200 inches (about 17 feet) in diameter at chest height and 250 feet tall. They make nearby ponderosa pines (which are very large trees) look like sticks. The giant sequoias dwarf everything else around them and disrupt an observer’s visual perspectives of their ecosystem. You know what you are looking at, but you can’t really believe it.

We walked around the circular path through the General Grant Grove and were in awe of the size and majesty of the trees. They were humbling and yet invigorating in the slowly failing light of the evening. There was a dusting of shed cedar seeds on the pathway and a clean smell of wet snow and rich, resinous wood all along the trail.

The roots of a large giant sequoia extend up to 100 feet around its trunk. Giant sequoias are not terribly affected by insects or diseases, and it has been said, possibly with some exaggeration but also with some truth, that no human has ever seen a giant sequoia die a natural death. An established tree is easily able to outgrow its surrounding competitors and withstand even the most severe forest fires because of its thick, fire resistant bark. They live their twenty or even thirty centuries in relative ecological peace.

Photo by D. Sillman

Water transport up the very tall trees is a very complex problem. Osmotic pressure from root-absorbed water can only rise several meters and capillary pressure in the small vessels of the xylem is only able to pull it partway up the tall tree trunk. The cohesion of the water column and the pull of transpired/evaporated water  from the upper needles can take the water somewhat higher, but very large trees also need to absorb water in the needles of their upper canopy typically from fog. The presence of regular fogs, then, is another critical site variable to allow the sequoia to attain their very great heights!

We climbed back into the car and drove past the outlying “sentinel” sequoias that guard the entrance into the parking area. We were all damp from the snow that had melted on our heads and coats and tired and hungry from a long day of travel. The next morning, though, before breakfast, Deborah and I drove back down to the grove on a very snow-covered and icy road to take some more pictures and feel the heights (and depths) of the trees. We were all alone with the giants for nearly an hour! It was glorious!



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Signs of Spring 12: California (part 1)

California Fish and Wildlife, Flickr

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California is an impossibly big and diverse place. Over its 900 miles of length there are a multitude of landscapes and habitat zones. Some of these are human dominated, and some are naturally pristine. Most of the state, though, is somewhere in between.  California has almost 40 million human inhabitants making it the most populous state in the nation, and its three trillion dollar/year economy would make it, if it were an independent country, the fifth largest economic system in the world (only the U.S. (even without California), China, Japan and Germany are larger). It is a place of cultural and social innovation and experimentation, and it has a trend-setting entertainment industry, great natural beauty and a stupendously productive agricultural economy.

California because of its natural seasonal cycles is normally a place of drought and wildfires alternating with torrential rains, floods and mudslides. Its eastern mountains are buried (usually) in tens of feet of snow each winter and great efforts are made to retain, disperse and use the melt water from these great snow fields to sustain the agricultural systems and human inhabitants of the state.

California is on the forefront of places in the United States being altered by our changing climate and rising global temperatures. Changes in the seasonal timing of moisture delivery might drive the state out of its normal weather cycles into exaggerated extremes of drought or flood. The impacts of these fluctuations on the state’s natural and agricultural ecosystems could affect the food supply for the entire world.

California because of its young, still forming geological base is also a place of earthquakes. Minor tremors and major upheavals have been recorded in both recent, human history and also in the ancient, geological history of the state. The potential for a nearly unimaginably large scale human disaster if (or some would say “when”) a major earthquake hits a densely populated region of the state is an acknowledged, although still insufficiently planned for, reality.

El Capitan in Yosemite. Photo by D. Sillman

I recently went out to California to spend a week with family and friends in two of the great national parks in the Sierra Nevada Mountains. Over the next few weeks I want to talk about my observations and impressions from this visit. Please recognize that I am leaving many more things out than I am including. Also note that I am a casual visitor to California and have no claim on even a low level of expertise about the state. I am focusing on just a few things of interest.

We flew into Fresno from Salt Lake City. The section of the flight up and over the Sierra Nevada Mountains was as rough and as turbulent a flight as I have ever experienced. You could picture the great masses of air coming from the distant Pacific Ocean, roiling chaotically up over the Sierras, releasing their moisture as clouds and rain and snow as they cooled high up in the atmosphere. The mountains were shrouded in clouds and the few peaks that emerged were jagged and snow covered. And this was late May!!

The air turbulence stopped almost immediately after we crossed the mountains, and the cloud cover dispersed. The land below us was flat and brown: the San Joaquin Valley. This is southern section of the great Central Valley of California. The Central Valley produces 8% of the United State’s total agricultural output (by value) and grows over 250 different crops! Almonds, grapes, pistachios, walnuts, oranges, peaches, tangerines, tomatoes and so many more fruits, nuts and vegetables are grown in the small, neatly cultivated, massively irrigated fields of the valley. We flew over a vast brown expanse that suddenly turned into some circular fields of green and then a continuous set of perfect rectangles that were crossed by lines and lines of dark green trees and vines.

Almond grove (Merced, California). Photo by Nehrams2020, Wikimedia Commons

Almonds are possibly the most important crop grown in California (it is an $11 billion industry), and I have talked about them before with regard to the need to import massive numbers of pollinators each year (see Signs of Fall 11, November 15, 2018). Almonds are also the most water demanding crop grown in California! The production of a single almond requires (according to a 2019 paper by Julian Fulton published in the journal Ecological Indicators) 12 liters (or 3.2 gallons) of water! And, almost all of this water is provided by irrigation! Growing almonds uses 10% of all of the water consumed in California!

Grapevines near Fresno. Photo by D. Prasad. Flickr

On the ground: we collected our rental car from the Fresno Airport and headed east toward Kings Canyon and Sequoia. Farms, vineyards and orchards dominated the countryside all the way to the mountains. The fields were incredibly well tended, lush and free of weeds. Vines of grapes and berries were carefully wrapped with protective netting. Trees were uniformly trimmed and pruned. To grow plants like this requires not only a large application of water but also significant fertilizer. The weed control (and primary pest control) were probably achieved by the extensive use of herbicides and pesticides. These careful, precise, idyllic looking farms were actually food factories being maintained by fossil fuels and fossil fuel synthesized chemicals along with tons of surface water pulled from the canal system that crisscrossed the acreage grids and also from ground water. Recent data shows that the ground level in this valley is sinking due to the extensive removal of ground water, and that many well casings are being crushed and rendered useless by the ongoing soil collapse.

The heavy use of agricultural chemicals (herbicides, pesticides and fertilizers) is also causing a drinking water crisis here in the valley. The New York Times reported in a May 21, 2019 article that more than 300 public water systems in California have unsafe drinking water primarily because of agricultural chemical contamination. Half of these failed systems are located right here in the San Joaquin Valley.  There is a steep cost for the perfection of these fields! Over one million people are affected by this drinking water contamination.

We drove for about 40 minutes and then began the steady climb up the western face of the Sierras. The Sierras have been described as a great table of granite that tilted many millions of years ago lifting its western edge up high above the basin of Nevada. The relatively gentle slope of the western side of the Sierras contrasts with the steep escarpments on the west. These high western edges are where the great valleys like Yosemite were carved out by glaciers and rivers. These high western edges are where we were going to see the rocks, waterfalls and trees of Yosemite, Sequoia and Kings Canyon.

Photo by D. Sillman

Fresno was just over three hundred feet in elevation. Soon we drove passed the one thousand and then two thousand foot markers and then on up to the six thousand foot marker in our climb up to Kings Canyon and Sequoia. The farms and orchards disappeared, replaced by a dry shrub land (“chaparral”) and then a dense coniferous forest. The sides of the road were covered with scattered and then increasingly deeper and more continuous snow. Finally, just as we entered a cloud layer just over five thousand feet, a light rain turned to a gentle snow.

The agricultural “factories” were far behind us. Now we were looking for giant trees!

(Next week: the giant sequoias of Kings Canyon!)


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Signs of Spring 11: Predators

Photo by Mythicmeadows, Wikimedia Commons

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The interaction of large carnivores with small and medium sized carnivores was explored in a wildlife population study conducted by Penn State University researchers (Penn State News, August 8, 2018). When a large predator (like a cougar or a wolf) is removed from an ecosystem (an occurrence that has been observed in most human-occupied habitats) there are a number of expected and unexpected consequences.

Expected consequences include the unregulated growth of primary prey populations that the large carnivore preyed upon. Here in Western Pennsylvania the exponential growth of white-tailed deer populations in our wolf-less and cougar-less biotic communities is an excellent example.

Less anticipated consequences of the loss of a large predator, but still quite logical, are the increases in numbers of small to medium-sized predators (like foxes, bobcats and coyotes) whose numbers had been kept in check by the direct or indirect actions of the larger carnivore. The unexpected consequences of these increases in these predators is the increasingly intense competition between them and possibly outright predation of the larger species on the smaller. Coyotes, for example, are extremely intolerant of red foxes and will kill any red fox that they come across. Shift of the predator profile away from the small predators to the medium sized predators can lead to explosive, uncontrolled growth of the small predator’s small prey species. Lack of red foxes, for example, could lead to large increases in mice populations which could, in turn, negatively affect an ecosystem’s plant community and possibly contribute to increases in diseases and parasites carried by the mice. Possibly the explosive growth of white-footed mice here in Western Pennsylvania (and the associated rise in black-legged ticks and Lyme Disease transmission) is a consequence of declining red fox numbers due to the local increases in eastern coyotes.

Golden jackal. Photo by C.J.Sharp, Wikimedia Commons

Similar observations on these consequences of large predator removal are being made in Europe. Wolves were effectively extirpated from the European continent by intensive hunting and poisoning campaigns. The removal of this large predator has allowed the golden jackal (Canus aureus)  a nearby, medium-sized predator to spread across Europe (see New York Times, January 11, 2019).

The golden jackal, a native of the Middle East and countries all across southern Asia, is a 15 to 30 pound canid (slightly smaller than a coyote) with omnivorous feeding behaviors that range from active carnivory to detrital and carcass scavenging. Golden jackals were first reported in Europe back in the 1800’s but have, since the middle of the 20th Century become very widespread. In the first two decades of the 21st Century, their numbers and extent of distribution have increased explosively.

Golden jackals are well adapted to not being seen. They live in small family groups typically of four to six individuals with one breeding pair, they tend to hunt alone, they are very furtive and they are nocturnal. They do have a tendency to howl, though, and this howling can be stimulated by other jackals or by other sources of noise (like church bells, for example). Golden jackals especially favor lowland habitats ideally near water (like a river, lake, canal, or the seashore). They also tolerate dry habitats, though, almost up to an extreme desert. They are not well adapted to snow, however, and must travel in the tracks of other animals when moving across a snow covered landscape. For this reason, many ecologists feel that the reduced snow fall and warmer temperatures in a climate changed world will favor the further proliferation and expansion of golden jackal populations.

Wolves attacking moose on Isle Royale. Photo by R. Peterson, Wikimedia Commons

And, finally, looking at some predators closer to home, it was reported in Science this past fall (Sept. 21, 2018) that the wolves of Isle Royale are going to be “rebooted” (their term, not mine!).

Isle Royale is a 206 square mile island in the northwestern corner of Lake Superior. Technically, the island is part of the state of Michigan, but functionally the main island and the hundreds of smaller islands around it make up Isle Royale National Park. Isle Royale is a patchwork of complex habitats and is the home for populations of moose and gray wolves that were each introduced to the island back in the early years of the 20th Century.

For the past 60 years the Isle Royale moose and wolves have been closely studied. The simplicity of their predator/prey dynamic and the isolated nature of their island habitat have enabled researchers to very precisely observe the population interactions and their ebbs and flows.

The ideal wolf to moose population ratio for an island the size of Isle Royale was calculated to be 25 wolves to 1500 moose. Over the six decades of study, though, this ratio was never achieved and population stability was never observed. Moose numbers fluctuated wildly from a low of 540 individuals to a high of 2450 individuals. Wolf numbers also careened up and down from an historic low of 14 wolves to a maximum of 50 wolves. This summer, though, there were only two wolves left on Isle Royale: an aging mated pair of closely related individuals (the female was the daughter and the half sister of the male). Although over the years new wolves have arrived on Isle Royale (either after a long, cold swim or an icy trot across the winter lake ice!), the wolf population on the island had succumbed to the insidious effects of severe inbreeding.

Photo by USDA Forest Service, Public Domain

The consequences of this decline in the wolves has been very predictable. The moose population has grown extensively, and grazing by this large number of moose throughout the park has caused a decline in habitat quality of the island. The island is not in  sustainable state!

After a long debate, the National Park Service has decided to “reboot” Isle Royale’s wolf population by introducing new wolves to the island. Some of these wolves will come from Michigan and others will come from Ontario, Canada. The 20 to 30 wolves that will be added to the park will have, then, a broad and diverse gene pool which will, hopefully, avoid the inbreeding problems.

None of these added wolves, though, will have had any experience hunting moose! It is expected, though, that they will quickly acquire moose hunting skills in this very prey limited ecosystem. As one researcher put it, “wolves are wonderful observational learners, and hunger is a strong motivator to test any potential prey.”

I will keep you posted!



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Signs of Spring 10: Bees and Herbicides and Pesticides, Bats and Viruses

Photo by Aqua Mechanical, Flickr

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Glyphosate is the active ingredient in the herbicide Roundup, and, not surprisingly, it is the most widely used herbicide in the world. Glyphosate functions by inhibiting the activity of a set of plant enzymes that control the synthesis of aromatic amino acids (tyrosine, tryptophan and phenylalanine). This disrupted amino acid metabolism, then, results in defective protein synthesis and ultimately causes the death of the plant. Since these glyphosate-affected enzymes are not found in animals, glyphosate, at concentrations used in herbicide applications, is alleged to have little effect on animals and is advertised as “safe” weed and grass killer. Many bacteria, though, have the enzymes that are affected by glyphosate and there is some concern that both soil bacteria and also microbiome bacteria could be affected by glyphosate applications.

Honeybee gut microbiomes have long evolutionary histories and have been strongly conserved over millions of years (see Signs of Summer 11, July 27, 2017). These gut microbiome bacteria are important as barriers against infection by pathogens and also in the chemical conversion of raw nectar into honey.

Honeybee. Photo by C.J.Sharp, Wikimedia Commons

In a paper published this past fall in the Proceedings of the National Academy of Science (September 24, 2018) a research group from the University of Texas showed that glyphosate exposure greatly reduces levels of a common gut microbiome bacterium in honeybees and causes those affected bees to be more susceptible to infections by pathogenic bacteria. These impacts may also affect the nourishment and energy levels of the bees and may even play a previously unrecognized role in the development of Colony Collapse Disorder.

These researchers also point out that glyphosate may impact the gut microbiome bacteria in many animal species. Studies looking at the impacts of glyphosate on humans, for example, should include along with possible cancer connections and neurodegenerative disorders, possible disruptions of the human microbiome.

In another paper published in Science last fall (November 8, 2018) researchers at Harvard University examined the impact of pesticide exposure on the behavior of bumblebees inside their nests. Using high performance cameras and coded markings attached to the backs of all of the individual bumblebees, the specific locations, interactions, and other behaviors of the nest bumblebees were recorded over a two week period of time. Twelve nests were set up in the laboratory with half of the nests having access to nectar sources that contained the widely used neonicotinoid pesticide imidacloprid. The other six nests were given access to nectar that did not contain imidacloprid.

Bumblebee queen. Photo by M. Cooper, Wikipedia Commons

The bumblebees that were exposed to imidacloprid were less active in the nest compared to controls and did not participate in nest maintenance or larvae care. Exposed bumblebees also had fewer social interactions with their fellow nest inhabitants. These altered behaviors were particularly noticeable at night while, interestingly, during the day especially as the experiment went on, pesticide exposed bumblebees actually behaved in increasingly normal ways.

Pesticide exposed bumblebees, though, were less able than controls to regulate the temperature of their nest. None of the bumblebees in imidacloprid exposed nests constructed the expected thermal insulating, waxy barriers that function to prevent cold temperatures from damaging developing larvae. Larval care and development, then, were significantly affected by the pesticide.

Exposure to imidacloprid has been previously show to reduce foraging activity in bumblebees with the consequential reduction in nectar and pollen gathering and the decline in the overall health and vigor of the nest. This impact has led the European Union to ban imidacloprid use in EU countries (see Signs of Summer 4, June 26, 2018).

Mexican free-tail bats. Photo by A. Froschauer, USFWS.

Bats have many very positive ecological roles. They are vital pollinators and seed dispersing agents, and they consume a vast number of potentially disease carrying and crop destroying insects (see Signs of Summer 1, June 7, 2013).

Bats also, though, have a few less positive ecological features. For example, they carry and disseminate, sometimes across vast distances, some of the most deadly viruses known to humans including Ebola, Marburg and the SARS corona virus. Bats carrying these deadly pathogens, though, never seem to be ill. Somehow they act as reservoirs for these viruses but never become victims. Virologists at China’s Wuhan Institute of Virology explored this resistance of bats to viral illnesses and published their results in Science.

Previous ideas about viral resistance in bats centered on two hypotheses: 1. Possibly a bat’s immune system can make large numbers of “naïve” antibodies (i.e. antibodies that did not yet have specific antigen recognition sites). These circulating, naive antibodies could then mediate the very rapid immune system destruction of encountered viruses. Or, 2. The high body temperatures seen in bats during flight might stimulate immune activity much like the body temperature elevations seen in fever. Unlike fever, though, this acceleration of immune activity could easily be stopped by simply landing and ceasing flight muscle contractions.

The virologists at Wuhan examined the fundamental genetic sequences of two very distantly related bat species and found a core of highly conserved (and, therefore, very important!) genes that act to regulate the bats’ immune systems. Central to the protein products of these genes was a regulator protein that is found in all vertebrate immune systems. This protein is called STING (“STimulator of INterferon Genes”).

STING detects strands of DNA and RNA that are in inappropriate cellular locations and then triggers an immune cascade that destroys them. Often these DNA’s and RNA’s are viral nucleic acids, but they can also be fragments from a cell’s own genome that may have broken loose due to metabolic disruption or stress.

Indiana bat. USFWS.

The bat version of STING triggers a much more subdued metabolic response than the STING from other vertebrates. Many pathogenic viruses, in fact, damage or even kill their hosts because of the uncontrolled immune cascades and inflammatory storms triggered by their STING proteins! Bats, possibly, can carry their wide array of pathogenic viruses because of their very mild STING response!

But why do bats have such a toned down STING response? Bats are the only flying mammal, and , apparently, the metabolic stress of flight especially through the generation of high levels of free radicals from very active mitochondria in their flight muscle cells, leads to repeated breakage of their cellular DNA with the subsequent leakage of the nucleic acid fragments out from their cellular nuclei. Bats, then, have evolved a muted STING response to enable them to tolerate these metabolic stresses of flight, and the unintended consequence of this adaptation is their ability to carry so many types of viruses in their bodies.

There may be another unintended consequence of these muted STING proteins and their extremely down-regulated inflammatory responses. Reduced inflammation may be one of the causes of the very long life spans seen in bats. Bats do live much longer than any other (non-flying) mammal of similar size.


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Signs of Spring 9: Sycamore Trees

Photo by Dwspig2, Wikimedia Commons

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The Ohio State University campus is a beautiful place to walk and wander, and I did a lot of each back when I did my Master’s degree there. One place on campus that I loved to go was south of the Oval down in a shady hollow near a pair of old and venerable sycamore trees. The trees had short, thick trunks that were five or six feet in diameter at chest height. The trunks branched four or five feet up into thick sets of spreading branches.  There was a bench nearby where on nice days in the spring and summer I would eat my bagged lunch and read something that was not related to ecology or soil science. I imprinted on these sycamores and felt very at home in their presence.

I found our recently that these trees went through an existential crisis back in 2010! They were marked to be cut down in order to build a temporary construction road for the expansion of the nearby medical center. Fortunately, I was not the only person who valued these trees! A group of Ohio State employees gathered 1500 signatures on a petition to save them, and the president of the university eventually agreed to revise the building plans. This crisis and petition led to the formation of OSU Campus Tree Inventory and the eventual certification of the campus as one of the  Arbor Day Foundation’s “Tree Campus USA” sites.

A lot of good, then, came from this very near destruction of these two hundred year old trees!

Pinchot Sycamore, Simsbury, CT. Photo by Msact, Wikimedia Commons

Sycamores are primarily trees of the forest rather than the city. You see sycamores alongside streams and creeks or on the slopes of ridges where seeps and springs make the ground wet for a good part of the year. In fact, European settlers looked for the distinct colors of the sycamore’s bark in order to locate springs from which they could draw potable water.

In the uncut North American forest sycamores lived for 700 or 800 years and attained great girths if not particularly spectacular heights. Many of these trees had trunks that were  14 or 15 feet in diameter. George Washington described a pair of sycamores in his diary when he was in the Ohio Valley in 1770. One was just shy of 45 feet in circumference (just over 14 feet in diameter)  and the other was just over 31 feet in circumference (about 10 feet in diameter).

Currently, the largest sycamore in the Eastern United States is growing in Ashland, Ohio. It is 129 feet tall with a 15 foot diameter and a 48 ½ foot circumference. It is a true giant even compared to the sycamores described by the early explorers of North America!

Photo by T. Mues, Flickr

A very interesting aspect of these old sycamores is that they tend to rot out their heartwood while maintaining a strong, outer, living wood shell. This forms cave-like hollows at the ground level and chimney-like cylinders up in the crowns. Many European settlers took advantage of these “sycamore caves” and lived in them sometimes for several years until they had amassed sufficient resources to build a cabin. There is a delightful essay about the American sycamore and early North American settlement in Luke Bauserman’s “The Weekly Holler” (January 15, 2017).

Many birds used the upper hollows of the sycamore trunks as sheltered locations for their night roosts and nests. In fact, it is likely that these sycamore “chimneys” were the prime nesting and roosting habitat for the chimney swift prior to the European colonization of North America. The European settlers brought  many things to North America and took away many others, but their chimneys were of great importance to the vertically roosting and nesting swifts especially after the large hollow trees of the “settled” forests were cut down to make way for a more agriculturally oriented existence.

London plane trees in Wadsworth Park. Photo by P. Halling. Geograph

The wild American sycamore has a human created (or at least human facilitated), urban doppelganger called the London planetree. The creation of this hybrid is somewhat shrouded in mystery and many silvics books and websites offer only vague hypotheses about when and where exactly the London planetree came into existence. There are a few forestry historians, though, who have pulled together some very logical ideas about the origin of this “other” sycamore.

The trade in exotic plants from North America began almost immediately upon the discovery and initial exploration of the continent. Avid gardeners in England and throughout Europe imported and planted North American plant species (including the American sycamore) side by side with native plant species and also many other exotic species from around the world.

Ben Venables in his 2015 essay on the London planetree in the web magazine The Londonist contends that John Tredescant planted both the American sycamore and the Oriental planetree in Vauxhall Garden in Kensington (London) in the early part of the 17th Century. These trees, then, by the mid-1600’s had cross-pollinated and self-hybridized to create the London planetree.

Van Gogh’s “Road Meanders at St. Remy.” Public Domain

The vigor and heartiness of the hybrid was quickly recognized. Its ability to grow and flourish in the soil and space-stressed confines of the city, and its ability to tolerate the often toxic air pollution of an urban environment made it an ideal choice for street-side and urban park planting. Over half of the city trees in London are London planetrees and many European cities (including Paris, Prague and Vienna) have extensive stands of London planes along their beautiful boulevards. Smaller cities also planted London planetrees as is reflected in a famous painting by Vincent Van Gogh entitled “The Road Meanders at Saint-Remy” (1889), a painting that is sometimes referred to as “The Large Plane Trees.”

Historical photo of Apollo Iron and Steelworks housing, Vandergrift, PA, Public Domain

Here in Western Pennsylvania many towns have London planetrees. Nearby Vandergrift, PA (a town designed by Frederick Law Olmsted) has a beautiful set along its curving streets. There are also some large London planetrees along Pittsburgh’s Allegheny River Boulevard. These trees lean out and over the roadway in a very disconcerting manner as they grow toward the limited sunlight  in the shady valley of the Allegheny River.


Sycamore on Rock Furnace Trail. Photo by D. Sillman

There are few simple ways to tell American sycamores and London planetrees apart. The most obvious, to me, is their bark. Both have patchy, peeling bark of white, brown, green and gray that easily distinguishes these trees from all of the other types of trees around them. The London planetree, though, has this type of bark all the way from ground level to high up into its branches. The American sycamore, on the other hand, has dark brown, deeply furrowed bark on its lower trunk and only displays the “sycamore bark” on its upper trunk and branches. Their leaves are different, too. American sycamores have large leaves that have a vague maple-tree appearance to them. They are broadly ovate with 3 or 5 shallow lobes and wavy edges with scattered teeth. The London planetree also has large leaves, but they are more deeply divided into 3 to 5 lobes with smooth edges and few teeth. The fruits of these trees are similar in appearance (brown, somewhat fuzzy balls that stay on the tree through most of the winter), but the American sycamore usually has single balls hanging from its branches while in the London planetree the balls are usually in pairs.

A number of tree guides stress that location is also a good way to tell the American sycamore from the London planetree. A sycamore-like tree growing in a city or town is likely to be a London planetree while one growing along a hiking trail or in the woods is likely to be an American sycamore.

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Signs of Spring 8: Nests

Bluebird nest. Photo by cbgrfx123, Flickr

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Over the past five years Deborah and I have gotten very familiar with many types of birds’ nests. Working with the Cavity Nesting Team at Harrison Hills Park we have found and described a variety of grass and twig spun nests, cup nests, moss nests and random stick pile nests inside of our nesting boxes and have been able to work out the identities of the birds who have constructed them.

Tree swallow nests. Photo by T. Schweitzer, Flickr

Bluebirds, for example, use fine grasses when they weave their tall, cup nests, while tree swallows tend to use coarser grasses and almost always include a large number of feathers (either their own or feathers from other bird) in their nests. Chickadees build their nests with a predominance of mosses, while house wrens simply fill the nesting box with a seemingly chaotic array of small sticks that, somehow, has enough room for eggs, nestlings and the incubating adult. House sparrows make relatively shapeless nests in part out of natural materials with a large amount of added, human-made trash (candy wrappers, string, ribbon and even cigarette butts (I’ll come back to a further discussion of cigarette butts in a nest later)).

Chickadee nest. Mrgfan, Wikimedia Commons

We started our Cavity Nesting Project in 2015, and none of us on the team had a great deal of familiarity with birds’ nests. Also, we were initially uncertain about whether we should leave previously used nests in the boxes through the season or remove them when their individual nesting cycle was completed. Several scientific studies had found that the presence of old nests actually encouraged subsequent nest formation in natural nest cavities and nesting boxes. Other papers, though, stressed that old nest removal was important to help control the proliferation of nest parasites.

After our first, early spring round of bluebird nesting in 2015 we did remove several of the nests and put them in sealed plastic bags so that we could take them away from the nesting sites (we did not want to attract nest predators) and then dispose of them. One bag, though, ended up on top of the garbage can in my garage rather than in the trash itself. After three or four days I heard a buzzing noise in the garage and found that the bag was now full of trapped, adult blowflies.

This inadvertent experiment indicated to us that blowflies were present in our nesting areas. Blowflies can be significant nest parasites and can cause not only debilitation but even death of nestlings. From then on we removed all old nesting materials and disposed of them in sealed plastic bags. The positive impacts of reducing these parasites, we assumed, more than offset the loss of the possible stimulus that the old nests could impart to the nesting birds.

Nests are, of course, the place where birds lay and incubate their eggs and nurture their nestlings. Many bird species make iconic, woven, cup-shaped nests. Many other bird species, though, make very different sorts of nests.

KIlldeer nest. R. Cameron, Flickr

Killdeer, for example, put almost no work at all into the construction of their nests. They may push a few stones or some sticks or vegetation around to make a small clear spot (called a “scrape”) in which they lay their eggs. The eggs are well camouflaged by their colors and patterns and are remarkably hidden even when out in the open. Many years ago Deborah and I and our children rented a summer cottage on Chincoteague Island and were noisily greeted by a female killdeer every time we stepped out of our front door. We knew that the female was protecting a nest somewhere in the front yard (a weedy, sand and pebble habitat that was maybe 1600 feet square). Over the week we were on the island, we searched carefully through the weed cover of the yard but never did find the nest.

Killdeer also make scrape nests up on the gravel roofs of the buildings. At Penn State New Kensington it is a loud Sign of Spring and Summer to be dive bombed by some of these roof nesters whenever you go out or in the doors of the Engineering Building!

There are other birds who make even less of a nest than the killdeer. Cliff nesting murres and guillemots simply lay their eggs on bare rock ledges. They rely on the shape of their eggs (pointy at one end and rounded on the other) to make sure that any rolling of the egg will simply take it in a circle (and not straight off the edge of the cliff).

Birds like cowbirds and old world cuckoos don’t make nests at all but instead deposit their eggs in the nests of other bird species. Cowbirds originally were birds of the prairies that followed the great herds of bison. They fed on the insects that were attracted to the animal herds or stirred up by their activity. The unpredictable timing of the herd movements did not allow the cowbirds sufficient weeks to nest and raise their young. Using the nests of other birds and letting those birds rear their young was a logical evolutionary solution to their nesting crisis. The alteration of the North American forests by European settlement, though, opened ecological corridors for the prairie cowbirds and allowed them to move out into a wide variety of habitats. Today cowbirds are found all across North America and are responsible for a significant proportion of the declining populations of many native song birds.

Short-eared owls hunting storm petrals on Genovesa Island

A few birds make nests in underground burrows. Storm petrels, for example, on the Galapagos Island of Genovesa make their nests down in the volcanic rock tunnels and are hunted both inside the tunnels and at their surface entrances by diurnally active short-eared owls. The lava tunnels provide the only protective cover on this rocky, treeless island and the petrels (and their predators!) have quickly adapted to using them.

Birds’ nests range in size from delicate, spider webbing and thistle, bottle-cap-sized nests of hummingbirds to great platforms of thousands of pounds of sticks piled high up in trees by bald headed eagles. Some nests are meant to be used just once, while other nests may serve a number of generations of nestlings.

What plant materials a bird uses to build its nest also has an impact on the health and success of the nestlings. In a paper published this past summer (Proceedings of the Royal Society B, June 6, 2018), researchers at the Max Planck Institute for Ornithology found that starlings reared in nests to which aromatic herbs (including hogweed, cow parsley and goutweed) have been added by the parents (or by the researchers) had higher red blood cell counts, more robust immune system functions and fewer bacteria than starlings reared in non-herb infused nests. Further, the parental starlings incubated the eggs and nestlings longer in nests that had the added herbs suggesting that the added herbs acted as a tranquilizer for the parent causing it to linger longer on the nest.

Nest made with human trash. K. Stuedel, Flickr

Also, a study published in the Journal of Avian Biology (June 20, 2017) looked at house finch nests in Mexico City. These Mexican house finches, like the house sparrows I mentioned previously in Harrison Hills Park here in Western Pennsylvania, add cigarette butts to their nests. These cigarette butts add nicotine (a powerful, “natural” pesticide) and other chemicals to the nests that reduce the numbers of nestling parasites (like ticks). Further, the study suggests that parental house finches may actually add cigarette butts in direct proportion to their perception of the parasite load in the nest!

So, it’s spring and there are nests everywhere doing the job in some obvious and some subtle ways to help rear the next generation of birds!








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Signs of Spring 7: The Cicadas Are Coming!

Photo by K. Schulz Flickr

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Every seventeen years the quiet parks and forests of Western Pennsylvania explode with sound. Over a four or five week period in May and June periodical cicadas (also called “seventeen year locusts”) emerge from their underground nurseries in densities of tens of thousands to several millions of individuals per acre and begin to generate a roar that blocks out not only most of the other sounds of nature but also the usual crushing din of human existence!

Pay attention, everyone! 2019 is a Cicada Year!

It is the male cicadas that are making all of the noise. Their sound producing organs are on the undersides of their rounded abdomens, and their buzzing is intended to attract female cicadas so that they can reproduce. The male cicadas’ bodies are hollow and act as resonance chambers to amplify the buzzing which can be as loud as ninety decibels (the equivalent of the roar of a nearby power mower or a small chain saw). The ability to generate noise of this magnitude has earned the periodical cicada the title of the “world’s loudest insect.”

There are over 1500 described species of cicadas in the world, but only seven are classified as “periodical.” The life cycle of a normal, “annual” cicada (like our yearly “dog-day” cicadas, for example (see Signs of Fall 1, September 6, 2014)) can span several years and typically includes an extensive larval stage in which the cicada lives underground feeding on the fluids of tree and other plant roots. In periodical cicadas this underground portion of the life cycle is stretched out to intervals of thirteen to seventeen years! These adult “magical” cicadas (their genus name is Magicicada!), then, spend their allotted month in the open air buzzing and reproducing after more than a decade and a half of dark, subterranean existence!

Photo by M. O’Donnell Flickr

Adult periodical cicadas have stout, black to brown bodies that are just over one inch long.  They have two pair of membranous wings that are tipped in orange. The front wings are twice as long as the hind wings and have an open span of about three inches. The head is dominated by a pair of large, bulging, red eyes. They are slow flyers and are easily taken by a wide range of predators.

There are seven species of periodical cicadas all of which are found exclusively in the eastern United States from the Great Lakes down to the Gulf of Mexico. The three species in the northern portion of this range tend to have seventeen year life cycles while the four species in the southern portion tend to have thirteen year cycles. There is considerable overlap in the ranges of these different types but little potential for interbreeding because of the asynchrony of the emergence of their adult forms.

In both the northern and southern ranges the cicada species form communities that have synchronously timed emergences. These cicada communities are called “broods.” These Cicada Broods were first described in the Nineteenth Century, and there is some controversy as to how many broods there actually are. Most authorities, though, agree that there at least twelve broods of seventeen year cicadas and thirteen broods of thirteen year cicadas. The broods are dynamic communities influenced by changes in climate and habitat. A number of broods have died out since their initial descriptions while others have come into relatively recent existence.

Photo by J. Sturner Flickr

The name “locust” is unfortunately used to refer to these periodical cicadas. “Locust” is an ancient, Biblical name for the grasshopper. The plague of locusts that beset the Egyptians in Exodus consisted of swarming clouds of voracious, plant consuming grasshoppers that decimated hundred of square miles of crops and forage. Early European settlers in North America seeing the unexpected emergence of thousands upon thousands of these cicadas thought that they were observing a plague of Biblical proportions and so named the insect “locust.”

The adult periodical cicadas, though, feed only moderately on plant fluids and do very little damage to trees or other vegetation via their feeding. They are also unable to bite/sting or otherwise hurt a human being! Limb scarring from egg laying and larvae emergence can open some trees up to infections, but that too is usually without very much serious damage except in very young trees or in delicate, ornamental tree species like dogwoods. Blocking access of the gravid females to tree limbs (by cheese cloth coverings etc.) can lessened potential cicada damage to vulnerable trees. Even the larvae feeding on fluids from the roots of their host trees do not seem to greatly affect the overall health or rates of growth of the trees.

The following is a scenario for the upcoming emergence of the Brood VIII periodical cicadas. Brood VIII is the synchronized community of periodical cicadas found throughout the counties of Western Pennsylvania:

In June, 2002 female cicadas gathered in wooded areas that were filled with the incessant songs of the males. The loudest songs and the largest gatherings of singing males attracted the greatest number of receptive females. After mating, the female cicadas used their saw-like, posterior, abdominal appendages (their “ovipositors”) to dig under the bark of limbs of oak or hickory or dogwood trees. Into each of these gashes they laid one or two dozen tiny eggs. Each female then moved on to another limb and then another and another until they had deposited their six hundred eggs into roughly forty different sites.

Photo by J. Gallagher Wikimedia Commons

By August, all the adult cicadas were all dead. The eggs that hadn’t been eaten by birds or ants, or rotted by fungi, or destroyed by the summer heat hatched into tiny, ant-sized larvae that fell unnoticed to the ground. The larvae then burrowed six to eighteen inches into the forest soil where, among the tree roots that will sustain them, they began a slow, steady growth and metamorphosis that would last the next seventeen years.

In April 2019, these larvae, now nearly fully grown, begin to dig their way back out of their soil home. In May, they will pause about eight inches below the soil surface, waiting for the just the right weather to stimulate their emergence out through their soil turrets and mounds. A nice, warm rain is often the trigger that brings the soil temperatures to 64 degrees and initiates the cicada’s final climb up into the open air. Once up on the soil surface, the cicadas undergo a four or five day metamorphosis into their short-lived, flying adult forms.

In June, the rolling, buzzing, and some say, maddening, chorus of the seventeen year cicada will once again fill the countrysides and suburbs of Western Pennsylvania. Those individual cicadas fortunate enough (mostly via dumb luck and sheer force of numbers) to escape predation by birds, snakes, spiders, skunks, fish, moles and even dogs and cats, will reproduce and set up, for 2036, another generation and another extension of their “magical” life cycle.








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Signs of Spring 6: Mourning Cloaks, Commas and Spring Azures!

Mourning cloak. Photo by M. Nendov. Wikimedia Commons

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Last spring (Signs of Spring 3, March 15, 2018) I talked about the evolution of the Lepidoptera (butterflies and moths). Fossilized lepidopteran wing scales have been dated to over 200 million years of age! This is very significant because the flowering, nectar producing plants which make up most of our modern day lepidopteran food base did not evolve until some 50 million years later! What could those earliest lepidoptera have been eating? The logical answer to this question is actually on display in the early spring when several species of butterflies emerge weeks before the flowering of nectar-producing wild plants.

Mourning cloak butterflies (Nymphalis antiopa) over-winter as adults. They find cracks and crevices in tree bark and fold themselves into these narrow, protective spaces to spend the winter in hibernation. In the spring they emerge, often when there is still snow on the ground, and sustain themselves for several weeks during which they mate and lay eggs.

The emerging mourning cloaks vigorously contract their thoracic muscles to generate body heat. They also conspicuously and very uncharacteristically bask in the sunshine with their dark, colorful, dorsal wing surfaces (purple to maroon edged by an inner line of iridescent, blue spots and an outer border of yellow or creamy white) exposed to incoming sunlight. The venter (underside) of their wings is a dark, striated blackish-brown with a pale, gray border. Typically, the mourning cloak at rest folds its wings together so that only the drab, camouflaging coloration of the ventral wings is visible to potential predators.

These early spring mourning cloaks, quite possibly like those first lepidoptera 200 million years ago, drink sugar-rich tree sap that runs from wounds or woodpecker holes in trees. They are especially fond of oak trees and oak sap. The mourning cloaks are often seen walking head-first down tree trunks searching for oozes of sap. Adult mourning cloaks also eat rotting fruit and flower nectar during the summer and are especially fond of the flowers of knapweed and scabiosa (“pincushion flowers”). Mourning cloaks, like many butterflies, also swarm muddy puddles and even animal feces from which they gather not only moisture but also vital salts and nutrients.

Mourning cloak on lemonade sumac. Photo by M. Dolly

Mourning cloaks mate shortly after emergence from hibernation. Males typically select a sunny perch from which they watch for females. There is a brief courtship, and then the fertilized female lays from 30 to 50 eggs in encircling clusters on the small branches of some selected host tree or shrub species. These eggs hatch into small, black caterpillars that have white speckles and a very dark, continuous dorsal line.

The caterpillars are voracious eaters and readily consume the leaves of the American elm, aspen, cottonwood, hackberry, paper birch, and several species of willow. The caterpillars grow rapidly and undergo four molts as they move through their larval instar stages toward their inactive pupal stage. The pupa is encased in a gray chrysalis which hangs from a thread attached to branches or some other type of overhanging structure. The metamorphosis into adults takes about 15 days.

The eggs laid in early spring will pupate and emerge as adults by early summer (June or July). These adults may enter warm-weather inactivity phases (“aestivation”) and then re-emerge as the summer begins to fade. They then feed very actively in order to build up fat reserves for their hibernation. An individual experiencing this type of life cycle pattern may live up to 10 months or more! This makes the mourning cloak one of the longest lived butterflies in nature! These June or July emerging adults, though, may also, depending on the climatological conditions or levels of habitat resources, skip the aestivation phase and proceed directly to mating and egg laying. This second brood of eggs, then, hatches into caterpillars which grow, pupate and metamorphose into adults by August or September. This second brood, then, feeds voraciously to prepare itself for the long winter hibernation. In the northern sections of the mourning cloak’s range one or two of these seasonal broods are common. In the southern sections of the range, however, up to three brood generations can be seen.

The North American and European distributions of the mourning cloak are both expanding into more and more northern regions. It is thought that these expansions are yet another observation of the biological consequences of human induced global warming.

Comma. Photo by D. Dunford, Wikimedia Commons

Emerging along with the mourning cloaks are the comma butterflies (Polygonia spp.). The comma, like the mourning cloak, can overwinter as an adult and thus can quickly take advantage of warm spring afternoons to feed on the sugar-rich flow of tree sap or early flower nectars. This gives the comma a fast start on its spring reproduction. Commas are especially found in moist woods in which there is an abundance of nettles growing on the forest floor. Nettles, along with elm trees and hemp plants, are the primary plants on which the comma caterpillars develop.

The commas (also known as “angel wings”) are less distinctively marked than the mourning cloaks. Their orange and brown dorsal wing surfaces, though, stand out clearly against the browns and grays of the early spring vegetation. Like the mourning cloaks, the commas have very drab, very inconspicuously colored ventral wings surfaces. When they land and fold their wings, they seem to disappear from sight.

Commas, also like mourning cloaks, have summer and winter generations. The eggs laid by the over-wintering commas hatch into caterpillars that feed extensively on their nettle or elm host plants. The final instars of these caterpillar stages then pupate and form chrysalises from which a “summer generation” adult emerges. These summer commas are recognizable by the predominately black, dorsal surface of their hind wings. They feed widely on nectar, tree sap and rotting fruit and may, also like the mourning cloaks, spend the very hot months of the summer in inactive, aestivative states. They mate and lay their eggs again primarily on nettles and elms, and the caterpillars from these eggs will pupate and emerge as adults in the early fall.

These “winter generation” commas typically have hind wings that are predominately orange in color on their dorsal surfaces. These adults fatten up and then tuck themselves into tree bark spaces where they hibernate through the winter.

Spring azure. Photo by D.G.E.Robertson. Wikimedia Commons

Another early spring butterfly here in Western Pennsylvania are the tiny (1 inch across) spring azures (Celastrina ladon). These stunningly beautiful butterflies have neon blue dorsal wing surfaces that seem to glow as they fly about. When they land, though, and close their wings, like the mourning cloak and the comma, the bright color (and to all appearances, the butterfly itself!) disappears as the pale white under-wing colorations blend into the surrounding, early spring browns and grays. The spring azure unlike the mourning cloak or comma, though, overwinters as a chrysalis and finishes its metamorphosis into an adult as the winter starts to warm into spring. The spring azure is primarily a nectar feeder that emerges a bit later than the mourning cloak or the comma, ideally timing its appearance with the earliest blooming spring wildflowers. If plants are not immediately abundant, though, it may get nourishment, like the mourning cloak, from mud puddles, leaves and even bird and mammal feces.

The early butterflies of spring! In many ways a recapitulation of how butterflies lived in their first 50 million years! Slurping up tree sap and nutrients from mud and fecal sources. Waiting for the flowers to come!




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Signs of Spring 5: Early Spring on Rock Furnace Trail

Photo by D. Sillman

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Deborah and I went down to the Rock Furnace trail last Saturday around noon. It was cloudy but warm (65 degrees) and quite humid. The weather forecast was for a zero percent chance of rain, but it sprinkled on us off and on while we were walking. There was no one in the parking area when we arrived, but five other cars pulled in and parked while we were out on the trail.

Down below the trail Roaring Run cascades noisily through narrow channels of rock and then spreads out and slows as it enters wider parts of its gully. It flows east and then arcs north to join the smaller Rattling Run at the old, concrete bridge deep in the hollow. Rattling Run comes in via its picturesque drop over Jackson’s Falls just a quarter of a mile or so up a side-trail that is now marked private property. The abundance of snow and rain this winter has filled the springs that feeds these creeks. There is a lot of water running in the streams!

We paused on the trail just before the climb up to the McCartney #6 gas well and looked down across one of the wider parts of the stream. A chorus of spring peepers echoed up from below and cascaded around us. The first peepers of the spring!

Spring peeper. Photo by Fyn Kynd, Flickr

Spring peepers (Pseudoacris crucifer) are small tree frogs that live around marshes, ponds, temporary pools and small streams throughout the United States (except for the deep southeast). They are very abundant here in Pennsylvania. Peepers have sticky foot-pads that enable them to climb up the trees, shrubs, and tall grasses that surround their “home base” water sources, and it is from these perches that the male peepers sing out their distinctive, spring mating songs,

The peepers’ mating choruses begin in early spring (around here usually in mid-March). They usually start up fifteen minutes or so after sundown and typically go on for a four hour period. I am not sure why these peppers were calling so actively at noon last Saturday except that it was a cloudy day and finally warm enough for frog activity! Their release from the cold temperatures of recent days and nights probably stimulated the frogs into an out-of-character day-time chorus!

Female peepers, attracted to the calling of the males, enter the calling area and select the individual with whom they want to mate. The male then clasps himself onto the female’s back and remains there as the female return to the water source to deposit her eggs. The attached male prevents other males from mating with the female and insures that all of the female’s eggs will be fertilized by his sperm. The female can lay between 800 and 1000 brown-colored eggs either singly or in clusters. The eggs can be set afloat in the pond water, attached to submerged vegetation, deposited in the muddy bottoms of pools, or even put into fluid filled tree hollows or many other types of available micro-pools. Down along Roaring Run the eggs will probably accumulate in small pools around the rocks. Many will probably be eaten, though, by fish!

The eggs hatch in six to twelve days. The emerging larvae (the “tadpoles”) will typically remain in their aquatic form for ninety to one hundred days. This larval incubation period, however, can be as short as forty-five to sixty days depending upon weather conditions, time of egg deposition, and conditions in the tadpole’s pool.  The tadpoles eat a wide variety of foods (including algae, dead vegetation, bacteria, fungi, zooplankton, flesh from animal carcasses, and even inorganic materials like sand). The tadpoles are, in turn, preyed upon by almost any organism that is larger than they are. Fish are especially significant tadpole predators in ponds and streams, but predaceous beetles, salamanders, and water snakes also readily consume the tadpoles

We listened to the peepers for several minutes before we detected a second sound in the frog chorus. It was a sharp “quacking” croak of the wood frog! The longer we listened the more clearly the wood frog calls stood out. For the past seven years we have gone down to Ohiopyle in March to look for wood frogs. We were just down there the week before, actually! How wonderful to hear them so close to home!

Photo by D. Sillman

Everything is brown and gray along the trail. The forest floor is littered with dry leaves, and the gray tree trunks (mostly red maple, yellow poplar and beech) stand in dense copses, incredibly uniformly sized (8 to 10 inches dbh) all along the trail. These trees are secondary or maybe even tertiary recovery relics from the wholesale cutting  back in the Nineteenth Century that was needed to generate the charcoal that powered the old iron furnace whose remains can be found on down the trail. There is also a stand of eastern hemlocks that may be a remnant of the hemlock forest that probably dominated this cool, wet ravine before the iron furnace was set up. Out in the surrounding acres of hardwood trees, occasionally a young hemlock can be found growing all by itself. These small trees are probably surprisingly old! If they last another three or four hundred years and actively drop their cones and seed around themselves, those hemlocks will be centers of ecological hemlock “crystals” that will reshape this forest back into a pure hemlock stand. All of the maples, beech and poplars that we see today, then, will then just be distant memories in the humus.

Photo by D. Sillman

It’s easy to spot the hemlocks. They are bright stabs of green in the brown and gray of the forest. Looking closer I see other patches of green, too. Evergreen wood fern, Christmas fern and polyploidy fern up on the sandstone boulders have kept their chlorophyll all winter. Many of the rocks and some of the fallen logs and stumps also have mosses growing on them. Many of the moss mats have recently sent up sporophytes (they are so new that they are still green!). The knobby sporangia on the tips of the sporophyte stalks will make spores that will disperse in the wind or in the rain and let the moss mat slowly increase its density and steadily expand its edges.

Spring beauty. Photo by D. Sillman

Spring beauty is in bloom! Its delicate little white flowers are hard to see at first, but once your eyes adjust to their presence they light up the forest floor. Chickweed is also in flower. Cut-leaf toothwort (“pepper root”) plants are up and in leaf but not flowering yet, there are also many violets that have not yet set flower buds. Interestingly, the usual “first flower” of spring, coltsfoot, is no where to be seen. There is a south facing trail-cut just opposite the McCartney gas well at the top of the hill where the first coltsfoot is almost always seen. No hint of its yellow flowers today, though.

There are drainage ditches alongside the trail that are full of still water. Often these ditches have salamander and toad egg clusters in the spring. Today, though, the water is clear and there are no egg masses.

It  is barely spring down on Rock Furnace Trail! All of the plant and animal signs of spring seem to be so much later this year than usual. Once we hit some warm weather, though, the pace of “spring-change” will be hard to keep up with!




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