Signs of Fall #3: Feral Cats

Photo by Stavrolo, Wikimedia Commons

Photo by Stavrolo, Wikimedia Commons

A couple of weeks ago I received an email from my friend and fellow environmental enthusiast Patrick Kopnicky asking me for my opinion about feral cats and their impacts on their environments. Patrick and his wife Mardelle, as I have mentioned in several previous postings, head up the Environmental Learning Center and the Friends of Harrison Hills organization at Harrison Hills Park (Allegheny County). The feral cat discussion that he was involved in centered on not only the maintenance of some area feral cat colonies but the proposed establishment (and support) of new colonies in some of the county’s other public parks.

So let’s get some facts lined up about feral cats. A feral cat is defined as a domesticated cat (Felis catus (or Felis sylvestris catus , if you prefer)) that has returned to the wild. A feral cat is not the same as a “stray” cat. Stray cats are domesticated cats that are lost or abandoned although the kittens of stray cats can, indeed, grow up to be feral cats. Feral cats typically live in colonies of three to twenty-five individuals. They are wild animals that live by consuming human refuse or by hunting small mammals, reptiles and birds (and it is the magnitude of this hunting that is the crux of the problem concerning feral cat populations!). It is estimated that there may be up to ninety million feral cats in the United States alone!

Photo by S. Golemon, Wikimedia Commons

Photo by S. Golemon, Wikimedia Commons

Some feral cat colonies are tended by human caretakers. These volunteers provide food, shelter and a degree of protection for the colony. Attention to disease and parasite prevention is also a part of this colony maintenance. These tended feral cat colonies are made up of animals that have very similar levels of health, vigor, and expected life spans that are seen in populations of domesticated (“house pet”) cats. A notable exception to this concerns rates of disease and mortality in kittens which are much higher in feral cat colonies than in “housecat” cohorts.

Cats are not native to North America. Feral cats, then, by definition, are alien, exotic species in our ecosystems, and they can have impacts on small mammal, reptile and bird populations that are, potentially, quite significant. The Smithsonian Institution and U.S. Fish and Wildlife Service released a study recently in which they estimated that up to 3.7 billion birds and 20.7 billion mammals are killed by cats in the United States each year. “Un-owned” cats (strays, feral cats, and barn cats) kill three quarters of these small animals while “owned” housecats are responsible for the remainder of kills.

Photo by Brisbane City Council, Wikimedia Commons

Photo by Brisbane City Council, Wikimedia Commons

Cats of all definitions are marvelously efficient hunters. It is this ability to hunt and kill that led the World Conservation Union to list the cat as one of the world’s one hundred worst invasive species. I have found a number of specific studies that correlate the presence of cats to the decline in the populations of many types of birds. One of the most compelling papers that I read described a seabird chick survival study set on two of the smaller islands in the Hawaiian chain. The island that had established populations of cats had a sea bird chick survival rate of 13%, while the island that had no cats had a sea bird chick survival rate of 83%. Cats are very active hunters!

An observation closer to home concerning the impacts of feral cats comes from a conversation I had a few years ago with John and Marilou McNavage. They told me (and recently confirmed that this is still the situation) that no longer had any chipmunks around their house. They correlated the lack of chipmunks to the presence of a near-by feral cat colony.

Now I have written about my two cats in this blog on a number of occasions. Two years ago I proposed “Housecat Day” as a logical (and ecologically sound) February alternative to Groundhog Day, and, as I write this, one of my cats is laying half across my computer key board and is purring so loudly that is hard to keep a train of thought going.
In short, I love cats very much! I also acknowledge, though, that they are incredibly efficient predators!

The Audubon Society endorses the American Bird Conservancy’s “cats indoors” campaign. The Audubon web site states that “worldwide cats may have been involved in the extinction of more bird species than any other cause except habitat destruction.” The American Association for the Prevention of Cruelty to Animals (“ASPCA”) states on their web site that feral cats mostly hunt and kill rodents not birds. The Smithsonian data listed above agrees with that: a cat will on average kill 5.6 small mammals for every bird. But, although the kill ratio seems to favor rodent control, the numbers of birds killed each year is still staggeringly high!

The ASPCA estimates that a feral cat without human intervention has an expected life span of about two years if it survives its time as a kitten. With human intervention and management of a feral cat colony the expected life span of the cats is ten years. The ASPCA also states that if a feral cat colony is eradicated (i.e. the cats are killed) a “vacuum effect” occurs and cats from outside the colony come into the area and rapidly re-establish the colony. Killing feral cats, then, only opens up resources for other feral cats.

The ASPCA and many other animal welfare groups advocate programs of Trapping…Neutering…and Releasing (“TNR”) as the most effective way to deal with feral cat populations (a variation on the TNR is “TVHR” (Trap-Vasectomy-Hysterectomy-Release) and there are studies that compare the relative effectiveness of each type of population control program). These types of programs have been used extensively in the United States and also in Europe. How effective are they? Studies in North Carolina and Florida showed 36% declines in colony populations in TNR treated feral cat colonies after two years and an 85% decline after eleven years. In Rome (the feral cats of the Coliseum!) there was a 32% decline in treated feral cat populations after six years.

TNR (or TVHR) works. The treated feral cat colony slowly declines in numbers and should, if there are no additional cats added to its population via stray or abandoned animals, result in the eventual extinction of the colony.

So what do I think about feral cats? Having some of these small predators in our ecosystems actually might be a benefit (we have far too many white-footed mice out there for, example, and these mice are important intermediate hosts for the bacterium that causes Lyme disease. Increasing predator control of these mice might be a way to get our local Lyme epidemic under control!), but having ninety million of these small predators out in our ecosystems is excessive. I personally could not go out and trap and kill a cat, but we need to control their numbers (via TNR and TVHR?) and also deal with the source of the feral animals, irresponsible pet owners who do not spay or neuter their cats and allow them to reproduce so excessively that the numbers of abandoned pet cats that head off into feral existences explosively increases each year.

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Signs of Fall #2 American Chestnut Trees

Forest History Society

Forest History Society

The American chestnut was once one of the most abundant trees of the eastern United States. It is estimated that up until the early part of the Twentieth Century thirty percent of the trees in our eastern forests were American chestnuts. It was a tall, although not the tallest, tree in the forest. It was a tree of great, spreading mass with huge trunks ten or twelve feet diameter and thick, extending, shading branches (as in the poem “Under the spreading chestnut tree, the village Smithie stands…”) that covered over remarkably large areas (Photo of virgin American chestnut trees used with permission from the Forest History Society).

The American chestnut also produced large numbers of extremely palatable nuts that were eaten not only by squirrels, birds, deer, and bears but also humans. These nuts were produced in abundance every year (unlike oak trees, say, that make their acorns over multi-year, boom and bust cycles), and many animals relied on this predicable production of chestnuts to sustain their populations.

The wood of the chestnut was strong as oak but lighter and more easily worked. The bark yielded tannins for small scale leathering, and even the leaves were thought to have medicinal value. It was a beautiful shade tree and was widely preserved and planted in the growing towns and cities throughout America.

Public Domain Wikimedia Commons

Public Domain Wikimedia Commons

In 1904, though, the American chestnuts lining the roads and walkways of the Bronx Zoo began to sicken. Their leaves withered and great lesions appeared in their bark. The trees then died one by one. They were the first recorded casualties of Chestnut Blight epidemic that swept through the eastern United States. There is evidence that the fungus responsible for this disease had been present in the southern U.S. since the 1820’s, but the death of the chestnuts in New York set off alarms that reverberated through the country. By 1950, the American chestnut was for all intents and purposes “gone.” It was no longer a reliable source of nuts or timber. It was no longer a tree of size and majesty.

The species, though, persisted even in the face of this awful disease. The fungus is transported either via insects or on the wind and infects a tree through cracks in its bark. The fungal mycelia then grow into the cambium layer of the tree (the part of the tree’s vascular system that transports sugars and nutrients). The tree responds to the infection by sealing off the infected cambium with a dense callus tissue, but the fungus grows faster than the callus and eventually the tree loses its ability to transport nutrients and dies. The fungus, though, does not affect the tree’s roots. New chestnut trees are thus able to sprout from the still living roots and stumps. Depending upon the site density of the chestnut trees and the abundance of the fungal spores, these new sprouts may grow for ten to fifteen years before the fungal infection kills them. They can reach heights of fifteen to twenty feet and can even produce nuts for several years before they die back. This growth and die-back cycle has caused the American chestnut to become more of a tall shrub than a tree!

Photo by D. Sillman

Photo by D. Sillman

Out in my yard and field I have had a small number of American chestnuts scattered among the oak, maple, apple, crab apple, locust, and spruce trees. Several of these trees have gone through cycles of growth and die-back in the 25 years I have lived here. Three trees, though, clustered into a corner of my field have lasted more than twenty years and to date have shown no sign of the fungus. They have grown to heights of 30 to 35 feet and last year produced an abundance of chestnuts in their spiky encasing burrs. I had to fight the squirrels for my share.

There are two associations that are working hard to develop a blight resistant American chestnut tree. The American Chestnut Foundation (which includes Penn State) and The American Chestnut Research and Restoration Center (which is based at one of my alma maters, The State University of New York College of Environmental Science and Forestry). Through incredible time and effort the scientists of these groups are now very close to developing American chestnut tree strains that are not affected by the blight. The thought that we might soon be able to re-establish these magnificent (and ecologically significant) trees throughout our eastern forests is one of the most hopeful and exhilarating pieces of environmental news that I have heard in decades.

For us here in Western Pennsylvania the nearby Chestnut Ridge might one day live up to its historical name! Let’s hope that our grandchildren will someday see it covered once again with American chestnut trees!

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Signs of Fall #1: Dog Day Cicadas

M.Szklanny Wikimedia Commons

Photo by M.Szklanny Wikimedia Commons

We have just passed though the period of the year that the ancient Romans called the “dog days” in honor of the rising of the dog star, Sirius, with the morning sun. They thought that the heat and often unbearable humidity of the late summer and start of the fall were due to the combined powers of these two stars bearing down on the Earth. It was said to be a time of madness when wine soured and both man and beast hovered on the edges of despair and rage.

Things are not really that bad, though. The rage and despair common to both students and teachers right now has more to do with the resumption of classes than with the celestial alignments. One positive aspect of these hot, humid days, for me anyway, is the emergence of the annual cicadas (called the “dog day cicadas”). Their buzzing songs high up in the trees gives a pace and a pulse to the hazy days.

The dog day cicadas have life cycles that range from two to five years in length. A given area, though, will have cohorts that reach their adult stages in the late summer of any given year. So, as we go through any given August, we will be greeted by the nearly continuous singing of the “annual” cicadas.

These cicadas begin their lives as eggs deposited in clusters under the bark of small tree branches and twigs. In six to seven weeks the eggs hatch into tiny nymphs which drop to the ground and burrow into the soil. They will live in the soil, feeding primarily on the sap from tree roots (especially oaks, ashes, and maples) for the next two or more years. They grow and undergo molts and metamorphic changes until at last they are at last ready to molt into their adult forms. In the late summer they crawl up out of the soil and climb back up the trunks of the same trees that housed their eggs and whose roots have nourished them for so long. On the trunks and branches of these trees the cicadas carry out their last molt and are transformed into adults. The dry exoskeletons of their pre-adult stages can often be found empty but still clinging to the rough surface of the tree bark!

Male cicadas climb further up the tree and begin to sing. They have thin, exoskeleton membranes (called “tymbals”) on the sides of their abdomens that they can pull inwardly and then release to make a loud “click.” The males’ bodies are also quite hollow and act as amplifying, resonance chambers for the generated sounds. The purpose of the song is, of course, to attract females for mating. The mated females will then lay their cluster of eggs under the bark of a twig or branch of the tree and start the life cycle all over again.

Hhaithait  Wikimedia Commons

Photo by Hhaithait, Wikimedia Commons

Interestingly, the females have very solid, “meaty” bodies. They require more metabolic energy and more elaborate internal organs for the production of their eggs. One consequence of these morphological gender differences is that females are the preferred food for most cicada predators (including birds, squirrels, raccoons, and even people (many cultures include annual cicadas as a popular, seasonal food! Pictured to the left is a dish of deep fried cicadas from Shandong, China ).

A few days ago I watched a blue jay flying hard after a swerving and twisting cicada. The blue jay had his beak open poised to grab the tasty insect when it eluded him by flying into a cluster of spruce branches. The cicada got away (for the moment, anyway).

The soils under our trees are quite rich with developing cicada nymphs and each year a significant number of them mature and emerge. It is thought that the species reduces its overall losses to predation by concentrating its adult emergence into a very narrow time window. Their numbers overwhelm potential predators and then they suddenly disappear. This transient existence also keeps predators from specializing on the cicada adults.

Other cicada species (called the “periodic cicadas”) have taken this idea of transient, predator satiation even further by extending their soil dwelling, nymphal stages out to thirteen or even seventeen years! These periodic “locusts” are so rarely abundant and when out are in such incredible numbers that predatory species are not only overwhelmed (and satiated) but also are stymied from evolving any specialized feeding strategies.

Species of these annual cicadas can be found all around the world. I was listening to a radio report from Liberia this morning. The story was about the West African Ebola outbreak, but the reporter couldn’t help but mention the beauty of humming cicadas high up in the trees all around her. The gentle throbbing of the cicadas formed a background for the gruesome details of the story and felt, to me, like a momentary song of peace against the horrors of the on-going epidemic.

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Signs of Summer 14: Red and Grey Squirrels

Photo by D. Sillman

Photo by D. Sillman

My family has a long history of providing food for birds and, often unintentionally, other types of wildlife, too. My father had a dozen bird feeders around his house in Arkansas and spent many enjoyable years of his retirement feeding and watching the birds. He also had an ongoing war of wits and weapons with the army of grey squirrels that descended onto his feeders every day. He bought “squirrel-proof” birdfeeders and even designed a few squirrel-blocking devices of his own (he was a very talented engineer), but none of them were successful. If the squirrels could not bypass or evade the blockages, they simply tore them apart with their sharp, relentless teeth. The squirrels even got used to my father’s noise makers and pellet guns and effectively adapted to the occasional feeding disturbances by scattering up into the surrounding trees until the prevailing Ozark quiet returned.

At first, I continued my father’s war on squirrels when I finally matured enough to have a yard and spot for birdfeeders, but finally I surrendered to them. The more I made the feeders “squirrel-proof” the more the squirrels were likely to destroy the feeders, and my bird feeding budget was far too modest to keep up with constant “hardware” replacement!
So, I put seed on the ground and even started spreading shelled corn and, in the winter, peanuts around for the squirrels. I also started admiring the incredible acrobatics that the squirrels employed daily just to get some mouthfuls of sunflower seeds! Hanging by one foot from the bottom of feeder, doing free-hanging sit-ups to reach the seeds must be a hard way to eat, indeed! The amazing thing is that once I accepted and facilitated the squirrels’ feeding, the wonton destruction of my feeders stopped and an acceptable (and visually entertaining) staus quo was established.

Photo by D.Dewhurst (USFWS)

Photo by D.Dewhurst (USFWS)

My son, Joe, was home a few weeks ago for a summer visit. He lives in Seattle now and is doing all sorts of things about which I am extremely proud (I’d list them here, but then I would run out of space for the rest of the blog posting!). Anyway, Joe was watching our front feeders one morning and noticed that there were only grey squirrels gorging on the corn and sunflower seeds. He remembered that when he was younger there was a mix of grey and red squirrels at out feeders, and that we often had problems with the red squirrels getting into our attic and chewing through window screens to get to the stash of birdseed on the porch. Where, he wanted to know, did all of the red squirrels go?

Sometimes you need some distance from a place to see its changes. Joe’s five summers away from home gave him just the right perspective, and he was right about the red squirrels. There used to be a rotating pattern of grey and red squirrels at the feeders. Now the greys were seemingly there all day! Watching closely, though, we did see a single red squirrel at the feeder in the later afternoon.

Where did the red squirrels go?

They are also asking this question in Great Britain, but we have to be careful about linking the two discussions. It is another case of “common names” and “scientific names” that we talked about in a previous posting (“True Names”). The “red” squirrel in Great Britain is Sciurus vulgaris. The North American “red” squirrel is Tamasciurus hudsonens. Very different animals!

In Great Britain the alarming decline in their red squirrels is due to two main factors: loss of coniferous forests (due to logging, land clearing, and climate change), and the introduction (in 1876) of the North American grey squirrel (Sciurus carolinesis). The loss of coniferous forests removes the principle food source of the red squirrel, the seed-rich cones of pine and spruce trees. The small red squirrel is well adapted to finding and gathering these cones and seeds and is able to out-compete most other seed eaters in these ecosystems. Red squirrels can live in deciduous forests, too, and are able to eat “mast” sources like acorns. They do not, however, digest these acorns very efficiently and, thus, have less food energy to sustain their activities and their rates of reproduction.

The introduction of the North American eastern grey squirrel to Britain was intentional but not historically clearly explained. The excitement of having an “exotic” squirrel species in the woods around Henbury Park, Cheshire is a likely explanation, but these grey squirrels responded as exotic invasive often do by multiplying and spreading all through their new habitats. Grey squirrels are now found in most areas of Great Britain. The grey squirrel does not directly interfere with or harm the red squirrels (in fact there are more recorded examples of red squirrels chasing off larger (although usually immature) grey squirrels from feeding areas than vice-versa). The grey squirrel does, however, consume a great deal of the seed and mast resources in a deciduous forest ecosystem and thus leaves less and less food for the less efficient red squirrel. So, as deciduous forests increased in Great Britain, red squirrels found it harder and harder to “make a living,” and their numbers declined. Grey squirrels also carry a virus that causes the disease called “squirrel pox.” The British red squirrels were not as resistant to this virus as the invasive greys, so the virus took its toll on the red squirrel numbers.

But, this isn’t exactly what has happened back here in Apollo, Pennsylvania!

The North American red squirrel like the British red squirrel does favor coniferous forests and does thrive when cones and seeds are available. The decline in coniferous forests in North America, though, has not been as extensive as it has been in Great Britain (although the long term impacts of climate change are casting a foreboding shadow over these ecosystems!), and the overall numbers of red squirrels in North America does not seem to be declining. North American red squirrels are moving into deciduous forest habitats but, as has been observed in Great Britain, they end up with less energy available for life processes are compete poorly against the more mast-adapted grey squirrels. Maybe most significantly, North American red squirrels are not as vulnerable to squirrel pox as the British red squirrels.

So what happened in Apollo? There is a local decline in red squirrels, but this decrease is not a part of a continental decline in the species’ numbers. What has happened here over the past decade?

As I discussed in a previous post, nine years ago a series of thunderstorms blew across our hill here in Apollo and knocked down eight (of the original twelve), fifty year old spruce trees (a mix of Norway and Blue spruces). My theory is that the removal of these cone and seed producing trees decreased the carrying capacity of our property for red squirrels. So, instead of having dozens of red squirrels running around (and chewing their way into the attic and porch) we now have just a few red squirrels that feed on the much smaller number of cone producing spruces (and whatever birdseed that they can glean).

The other side of Joe’s observation (that the grey squirrels are so abundant) may be due to the growth of the new oaks trees where the spruces once stood. These trees, as I have also previously mentioned, are starting to produce acorns and are, thus, increasing the food resource base for the acorn-loving grey squirrels. Another possibility to explain the surge in the numbers of the grey squirrels is the recognized détente between them and me. All of those scoops of sunflower seeds, piles of shelled corn, and bags of peanuts must have an impact on the grey squirrel biomass!

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Signs of Summer 13: A Monarch Update and True Names

Photo by D. Sillman

Photo by D. Sillman

Monarch update! There have been several monarchs fluttering around my stand of milkweed plants. I am watching closely for caterpillars! These will be the larvae of the migrating butterflies, the ones that will fly all the way to Mexico. I am sure that one of the monarchs was a female, and I hope that she was laying eggs!

But, back to this week’s blog!

There are two kinds of names for biological organisms: common names and scientific names. Common names are familiar, usually generalized, and are easy to remember. Scientific names sound like Latin (because most of them are!), are hard to spell and pronounce, and are often very difficult to remember with any degree of precision. So why don’t we just use common names?

Let’s think of the common name “red worm.” That name fits two different species of earthworms, a roving “bristle worm” found in estuaries, a large nematode parasite found in herons and egrets (and a bunch of intermediate hosts, too), and a thin, freshwater sediment dwelling worm that is an EPA indicator species and often used as fish food. And, that’s just a partial list! So, if I wrote an essay about a “red worm” there would definitely be a high level of uncertainty about what organism I was discussing.

That’s where the Latinized, scientific names come in. While their spellings and pronunciations seem more than a bit strange, they always refer to just one type of organism! So if we say Eisenia foetidia or Lumbricus rubellus we know which type of “red worm” earthworm we are referring to. Or, if it’s Neris diversicolor, or Eustrongylides ignatus, then we know that we are talking about the errantial polychaete out in the estuary or the parasitic nematode in a blue heron. Or, if it’s Tubifex tubifex, we know that we’re talking lake or river sediment worms (or fish food).

There are lots of rules for writing scientific names. One very important one is that they are written in italics (or underlined). It’s like the title of a journal, or a book, or a web site in a bibliography, the italics sets the scientific name apart and emphasizes its singularity and importance. I’ll save the other rules for my biology students, but it is quite amazing how often they are ignored in newspapers, magazines, web sites, and sophomore biology research papers!

So, in my postings for this blog I have tried to be as precise as possible as to which species I was talking about. I try to include the scientific name in the post (and work very hard to spell it correctly!).

There are, though, two very different views of scientific names in biology, and these views seem to be based on a degree of appreciation of the importance of organisms in our view of life. It’s very interesting to realize that there are many biologists who really have had no training in or experience with actual, living organisms! These molecular biologists live in a world of proteins and nucleic acids and are exploring the depths of the reality of life well away from the requirements of looking at intact animals, plants, fungi, or even bacteria.

A great example of this new type of biologist is the person who led the team that sequenced the genome of the Neanderthals, Svante Paabo. In his book (Neanderthal Man: In Search of Lost Genomes) he refers to the instructions that he gives to his graduate students who use Latin, scientific names in their manuscripts, “I always delete the Latin and sometimes even snidely ask who they are trying to impress by saying Pan troglodytes instead of chimpanzee.” Now Paabo is a brilliant molecular biologist, and his book on the search for the Neanderthal genome is excellent, but his attitude toward zoology in general (he admits to not knowing that insects were animals) and taxonomy in particular (“a sterile, academic exercise”) needs some expansion.

Carl von Linne (Public Domain)(Wikimedia Commons)

Carl von Linne (Public Domain)(Wikimedia Commons)

In another book, The Species Seekers, by Richard Conniff the religious fervor of Carolus Linnaeus (to use the Latin version of his name!) and his students to both see and describe (and name) all of the species on Earth and to put them in a taxonomic order “for the greater glory of God” is vividly described. Many of Linnaeus’ students were so driven by this quest that they committed themselves to some of the far ranging voyages of exploration of the Eighteenth Century (and about half of them died on these expeditions!). Theirs was not a sterile exercise, but a flesh and blood drive to see and know!

Reality, as is usually the case, is somewhere in between these two extremes. We need to appreciate the detail and meaning of our scientific nomenclature without having to throw ourselves out to sea in leaky, wooden boats.


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Signs of Summer #12: Green Apples, Symbioses and the Gene Pool

Photo by D. Sillman

Photo by D. Sillman

Deborah and I were sitting out on our deck a few nights ago watching the flurry of activities that always precedes sunset. The main event of the evening involved two squirrels playing tag and chase up in one of the apple trees down in the orchard. They were bumping into each other, jumping over each other, and just having a great time. They shook the branches of the apple tree so hard with their acrobatics that a steady rain of tiny, green apples poured onto the ground. Standing under the apple tree were two fawns, and they were happily eating the sour, green apples as quickly as they fell.

Squirrels and deer interacting via the apple tree, who would have predicted that?

Ecology is the scientific study of the interactions going on in an ecosystem. These interactions can be between organisms and also between an organism and the non-living parts of its environment. A word that has grown in meaning over recent decades is “symbiosis.” At one time symbiosis meant two species that interacted and benefited each other, but now it defines all types of interactions between species. Symbiosis, then, is the essence of what is studied in ecology! Symbiosis is what was going on in and under our apple tree!

Looking out at my yard and field I can see many examples of symbioses. There are the young oak trees shading out the older spruce trees and grape vines wrapping up and over the crowns of the arbor vitae (both are examples of “perfect competition:” one species will “win” and one species will “lose”).

Photo by D. Sillman

Photo by D. Sillman

There are lichens growing on the rocks and also on a number of the tree trunks around the yard. Lichens are fungi that have algae living inside of their cells. The fungus relies on the algae to make sugars via photosynthesis, and the algae rely on the fungus to give it a place to live. Both organisms benefit from this interaction. It is a type of symbiosis called “mutualism.”

There is a cardinal’s nest up in the branches of one of the blue spruce trees. This interaction is a great benefit for the cardinal but has no real impact on the spruce. When one species is benefited in an interaction and the other is unaffected this sets up a symbiosis called “commensalism.”

On the ground beneath the spruce tree a robin pulls an earthworm out of my leaf pile. This is a symbiosis called “predation.” The robin benefits but the worm is harmed.

In any given time frame in an ecosystem a whole array of symbioses will occur. Out front in the yard a sharp-shinned hawk flies from her perch near the top of the spruce tree and dives down toward the birdfeeder. A blue jay perched in the lilac bush near the feeder sees the hawk coming and screeches an alarm. The feeder birds have an extra second or two to fly into the protection of the arbor vitae or scattered out across the street away from the hawk’s dive path. The hawk does not get a kill, and flies off chased out of the area by several blue jays including the one that raised the initial alarm.

The hawk gets negatively affected in all of these interactions (no supper and a blue jay chase squad ruining any chances for another attack!). The feeder birds are benefited in their interaction with the blue jay, but how does the hawk or the feeder birds in turn affect the blue jay? I would say that they didn’t affect him at all. Now, if there had been blue jay fledglings or some flock members at the feeder, then there would have been a self-benefit in sounding the alarm, but there weren’t. So, the interaction between the blue jay and the hawk generates harm to the hawk and no effect on the blue jay (a symbiosis called “amensalism”).

And, what about the observation that started this whole flow of ideas: the squirrels and fawns around the old apple tree? What kind of symbiosis is this? The fawns are definitely benefiting by the fresh abundance of apples, and the squirrels are neither harmed nor helped. So, it’s another example of commensalism! And what does the apple tree get out of this? Its fruit have seeds that are spread around the yard, the field, and the whole neighborhood in the feces of the deer (there is a lot of deer feces everywhere!). The apple tree, then, gets the chance to generate new apple trees far from the parental tree. The deer are benefited, the apple tree is benefited, so it’s another example of mutualism!

In an ecosystem there is a complex matrix of interactions that often influence each other in unexpected ways. The impact of predators on their prey species is a great example of this. Take our sharp-shinned hawk and the bird feeder community of small bird species. Sharp shinned hawks swooping in on a feeder are most likely to take the slowest, the least experienced, or the individuals that are physically impaired as their prey. The individuals most likely to survive the attack are the healthiest or the “most fit” individuals. The impact of a predator that is in balance with its prey populations, then, is improvement of the quality of the prey’s population! This has been observed in birds around suburban bird feeders, it has also been observed in the elk in Yellowstone after wolves were introduced, and in wildebeests in Tanzania in areas where a healthy population of lions are active!

I am glad that there are no lions lurking in my back yard, but it is good that there are small predators working the flocks and clusters of the various prey species out there. I like to think that my yard will have a very healthy, nimble, and fit chipmunk population because of the predation pressure exerted by my cat, Mazie, and that maybe my dog Izzy’s impact by chasing rabbits around the field each morning will be to make the rabbits more alert and somehow wilder. Izzy has never come close to catching any of the rabbits, of course, and probably wouldn’t know what to do with them if she ever did! But, if ever one of the rabbits was slow (or stupid) enough to be caught by a scatterbrain terrier who runs with her eyes closed, then the removal of that individual from the population would do nothing but improve the gene pool!

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Signs of Summer 11: Turkey Vultures

Photo by Dori Wikimedia Commons

Photo by Dori Wikimedia Commons

The turkey vulture (Cathartes aura) is a bird that everyone knows and almost no one loves. They are a joy to watch soaring along in their great circles across the sky, but the closer you get to them the less majestic they seem! They are large birds (they weigh up to four pounds and have wing spans up to six feet) and are the most abundant and most widely distributed avian scavenger in the New World. They are easily recognized on the ground by their featherless, red heads and in the air by their broad, “eagle-sized” wings that characteristically wobble just a bit as they soar in great circles in the updrafts.

Turkey vultures are found all across southern Canada, the continental United States, Mexico, Central America, and down South America to Tierra del Fuego. Birds in the northern regions of this broad distribution migrate to warmer habitats in the winter while birds in the warmer to milder regions of this range stay in place all year round. The vultures from the northeastern United States tend to overwinter in Florida or Texas, while birds in the northwestern United States migrate all the way down to South America possibly as far as Argentina. Migrating flocks can be extremely large (thousands of individuals!). Turkey vultures, though, cannot fly at night (they require the thermal updrafts generated by the heat of the day) and, so, each day along their migration routes they must seek out secluded roosts as evening approaches.

Photo by M. Baird Wikimedia Commons

Photo by M. Baird Wikimedia Commons

Hinckley, Ohio (a small town just south of Cleveland) celebrates the spring return of their turkey vultures with a “Return of the Buzzard” day on March 15. For the past fifty-seven years they have been greeting the returning flocks of turkey vultures as an important sign of spring. It makes more sense than Groundhog Day, that’s for sure (although it less aesthetically pleasing than House Cat Day!).

The turkey vulture is an extremely gregarious bird. They roost in large, communal groups in specific locations that may be used for many generations. During the day, smaller, foraging groups of turkey vultures may pause in the high branches of a tree or on the roof of an abandoned building forming a group called a “wake.” Actively foraging and flying turkey vultures assemble in great flocks that can rise together in circular paths in the thermals of the heated atmosphere. These swirling flocks are called “kettles” because of their resemblance to water boiling up in a heated pan.

Turkey vultures are very long-lived birds. Life spans up to 25 years have been recorded. They have few predators except for a “usual suspects” list of potential nest predators (raccoons, skunks, foxes, opossums, snakes, etc.). They are relatively timid birds who will, if challenged at a carcass by another scavenger (like an eagle or a black vulture), regurgitate their ingested materials for the challenger to consume. At a carcass, turkey vultures feed in an organized, individual manner. Turkey vultures waiting for their turn at the carcass are exhibiting a behavior called “queuing.” Turkey vultures respond to threats and danger primarily by vomiting on the source of the danger. Since their stomach contents are typically acidic slurries of dead animal flesh, this behavior is quite an effective deterrent against aggression.

The impact of DDT on egg shell stability reduced the turkey vulture population slightly, but the banning of this pesticide has led to a completely recovered and, possibly, growing worldwide population. Potential lethal impacts of lead ingestion (from bullets and pellets in hunter-killed animals), though, are possible threats to turkey vultures. Turkey vultures have also been killed by farmers and ranchers out of concern that these carrion consuming birds will spread pathogens and diseases from carcass to carcass. The great efficiency of the turkey vulture’s digestive system, though, very effectively destroys ingested pathogens (turkey vulture fecal materials are completely free of any pathogenic organisms).

Turkey vultures use their extremely well developed sense of smell to locate a carcass. This is most unusual since most avian scavengers and birds of prey utilize vision to find their food. This reliance on scent detection explains why foraging turkey vultures soar at lower altitudes than other types of vultures, and it may also explain their “wobbling” behaviors in flight (this motion may increase their ability to detect and precisely locate a scent source). Use of scent also enables turkey vultures to find buried or cached carcasses that had been hidden by some terrestrial carnivore. The greater abundance of turkey vultures in open or semi-open landscapes is also probably related to their particular method of finding food. Highways all over North and South America have become prime foraging habitats for this species.

Turkey vultures have extremely weak feet and blunt talons. Thus, they are not able to readily kill prey or rip at a carcass with anything other than their sharp, curved beak. They also show a distinct preference for relatively fresh kills and will not readily consume rotting carcasses.

Turkey vultures mate for life, but upon the death of a partner an individual may take a new mate. Courtship behaviors include a “dance” involving raised wings and feet and long, following flights led by the male. Nests are located in individually selected locations not far from the pair’s communal roost. The term “nest” might actually be a bit of an exaggeration in describing the egg site for a turkey vulture. It is typically a site located on the ground (in a cave, hollow log or tree stump, or in a dense mass of vegetation) where soil and leaf litter and pieces of rotting wood have been pushed aside to make a spot for the one to three laid eggs. In a given area there will be relatively few specific locations that will suitable for a turkey vulture to build its nest. A chosen site, though, may be used for a decade or more. Both parents incubate the eggs and also the nestlings. Both parents feed the rapidly growing young. Incubation time is between 28 and 40 days, and nestling developments times are between 60 and 84 days. So, at a maximum, a reproducing pair of turkey vultures may spend over four months in intense breeding and rearing of their young.

Turkey vultures are not beautiful to look at, they make no beautiful songs (in fact they lack the organ of song generation (the syrinx) completely!), they eat dead animals, they smell bad, and if you get too close to one it will vomit on you (did I mention that they don’t make very good pets?). They are, though, beautifully adapted to their scavenger role in our ecosystems and have many good if not noble traits. They form lasting social and mating bonds, they are very good parents, and they even have excellent “table” manners at a carcass!

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Signs of Summer 10: Campus Nature Trail, Succession, and Existence

Photo by D. Sillman

Photo by D. Sillman

The Campus Nature Trail is celebrating its 30th year of existence this coming academic year. The group of students who worked so hard in 1984 and 1985 to visualize, fund (via University grants), and then build the trail are now in their late forties and, hopefully, are getting ready to send THEIR kids to Penn State! The Alcoa Foundation has over the years twice contributed funds to help us expand and mark the trails and set up the web site that has become known as “The Virtual Nature Trail.” Alcoa’s help has been critical to the existence and quality of our trail!

I could go on about all of the students who have used the trail for credit and non-credit classes. I could talk about all of the student research projects that have been conducted there! I could talk about the Boy Scout groups who have earned their forestry and environmental science merit badges on the trail or about the two Eagle Scout projects that so greatly improved it. I could talk about the Kids in College classes, the FIRSTE Program nature walks, the Backyard Bird Counts, the Neighborhood Tree Counts, and the Penn State New Kensington Arboretum all of which were centered on the Nature Trail, but you get the idea that it has been an intensely used and very significant teaching and learning resource for many levels of the campus.

What do we see out on the trail? Our first theme (that was described in the brochure that I wrote on a Commodore 64 computer and printed out on a dot matrix printer back in 1984) was succession: the observation that ecological change is triggered by certain species modifying other species’ limiting factors. This was most apparent at the boundary lines between the European black pines that were planted at the top of the trail during the construction of the campus and the mixed hardwood forest (white ash, yellow poplar, black cherry, etc.) that was growing all along the surrounding ridge. The pine forest that was so well established in 1984 is now almost gone because of disease, stress, shading and aging of the trees. The forest floor that was absolutely clear of all undergrowth in 1984 is now a thick vegetative jungle of shrubs, vines, and hardwood seedlings and pole trees. Succession in just three decades has completely reshaped the forest!

The young forest of ash, poplar and cherry is also changing. I was out on the trail yesterday clearing the paths of this wet summer’s plant growth and noticed that oak seedlings (mostly red oaks and white oaks) are growing in great numbers under the mixed hardwoods. They will form the forest that will overtake the ash, poplar, and cherry when we celebrate the one hundredth anniversary of the trail in 2084 (September 4, 2084, at noon! Mark your appointment books!).

Photo by D. Sillman

Photo by D. Sillman

Kirk Dineley, a student from the early 1990’s who is now an Associate Professor in the Department of Pharmacology at Midwestern University in Chicago, (he’s the sixth person from the right in the back row of the clean-up crew picture) sent me a quote from “Life and Fate” by Vasily Grossman that puts forest succession into the a whole new light:

Once, when I lived in the Northern forests, I thought that good was to be found neither in man, nor in the predatory world of animals and insects, but in the silent kingdom of the trees. Far from it! I saw the forest’s slow movement, the treacherous way it battled against grass and bushes for each inch of soil . . . First, billions of seeds fly through the air and begin to sprout, destroying the grass and bushes. Then millions of victorious shoots wage war against one another. And it is only the survivors who enter into an alliance of equals to form the seamless canopy of the young deciduous forest. Beneath this canopy the spruces and beeches freeze to death in the twilight of penal servitude. In time the deciduous trees become decrepit; then the heavyweight spruces burst through to the light beneath their canopy, executing the alders and the beeches. This is the life of the forest – a constant struggle of everything against everything. Only the blind conceive of the kingdom of trees and grass as the world of good . . . Is it that life itself is evil?

As I have previously written, there is no morality in nature although we can find metaphors for the meaning of our existence in the ecosystems around us. We can see and embrace examples of all sorts of opposing observations: change vs. constancy, cooperation vs. competition, and altruism vs. selfishness. We are a part of all of these and we are, astoundingly, also set apart from them. The debate about whether we can choose our paths or whether we are like the trees in a forest and are simply pushed along in an existence determined by our environment has compelling arguments on both sides. That we can consider this at all reflects, to me, something that approaches truth.

So, Happy Birthday, Nature Trail!! The trails on the campus side of the stream are all open and passable, please go out for a walk and tell me what you see!

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Signs of Summer 9: More Snakes!

Carl Meyerhuber is a longtime friend and teaching colleague, and he is also a lifetime reptile lover. Carl told me last week that he had found an old Pennsylvania Fish and Boat Commission pamphlet that listed and described the five most common snakes of Pennsylvania (a copy of this pamphlet, by the way is available on line ( ). He asked me to name which snakes I thought would be on the list, and I only got three out of five!

Photo by Mike Pingleton (Wikimedia Commons)

Photo by Mike Pingleton (Wikimedia Commons)

The three that I knew were the black rat snake (called the “eastern rat snake” in the pamphlet), the eastern garter snake, and the northern water snake. These are three snakes that I have seen frequently and up close in a wide range of habitats throughout Western Pennsylvania. These are also snakes that I have written about in this blog and on the Virtual Nature Trail species pages. The two, “most common” snakes that I didn’t know are species that I have almost never seen in the wild: the eastern milk snake and the northern ring-necked snake.

Carl and I talked about the milk snake and were both quite surprised that it was on the “most common” list! I had only seen one milk snake here in Pennsylvania, and Carl had never seen any! “My” milk snake was disturbed out of a well mulched azalea bed right next to my house. We were pulling out some azalea bushes in order to clear the way for the construction of a wooden porch deck, and the snake, a brightly colored, red-black-yellow banded individual that was about 2 feet long, quickly moved out of its hideout in the mulch and headed down into my orchard and burrowed into a pile of leaves. I hadn’t seen that snake before that afternoon (even though it was living right next to my house!) and I haven’t seen it since! (My hope is, though, that it is living under the deck right now!).

So why hadn’t I seen that milk snake before, and, why hasn’t Carl, a great observer of snakes and turtles in his yard and along local hiking trails, ever seen one of these snakes? They are big snakes (two to five feet long!) and so brightly colored that they always stand out against grass or leaves. They live all across Southern Canada, and in all of the continental United States, Mexico, Central America, and northern South America! They are opportunistic feeders that eat everything from rodents to birds to frogs to other snakes, and they live in a wide range of habitats.

So why don’t we see these bright colored generalists everywhere? The simplest explanation is that milk snakes are nocturnal. They are active when we are, basically, not!

Now I just thought of a good question: why is a nocturnal snake so brightly colored? Those colors would be hardly observable in the dark, what evolutionary role could the milk snakes bright colors play?

My best answer is, “I don’t know.”

Maybe the colors help to camouflage it in its day-light hideouts? (unlikely). Maybe the colors startle potential predators that might come upon it during the day? (the more brightly colored snakes escape from the predators?) (possibly). There are a good number of possibilities and maybe’s here (and it’s speculation like this that makes science so much fun!!)

Photo by David Hoffman (Flickr)

Photo by David Hoffman (Flickr)

Carl and I talked for a while about milk snakes but didn’t get to the northern ring-necked snake. It turns out, though, that the ring-neck snake is also nocturnal. They are smaller than milk snakes (only ten to fifteen inches long) and dark colored (except for their eponymous yellow ring around their necks), and they live quite quietly under logs, and rocks, and dead vegetation especially in wet forest habitats (although they can live in many types of forest and field ecosystems). Estimates of the numbers of ring-necked snakes in a prime habitat range from 28 to over 700 individuals per acre! That’s a lot of snakes! In many regions of the United States they are by far and away the most abundant snake species! They are found extensively over the northeastern half of the United States and southern Canada, but are very poorly known and seldom observed even by those of us who might be out there looking! Like the milk snake, they are a companion species in our ecosystem, but they are active out of phase with us in time!

So, when we cluster around our campfires (or lit decks or porches) we should remember that just outside the edges of the comforting glow of light are any number of species that are thriving, mostly invisibly (to us). Raccoons and possums are slipping by in the shadows, coyotes, are padding past undercover, and great snakes like the milk snake and the ring-necked snake are slithering past keeping rodent populations (and maybe even each other!) under control and within stable bounds.

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Signs of Summer 8: Bald Faced Hornets!

Photo by Carney Lentz (Flickr)

Photo by Carney Lentz (Flickr)

I wanted to start this posting with a description of a nearby bald faced hornet’s nest. So, I walked around in the woodlots bordering my fields, and walked up and down the campus Nature Trail and was very surprised not to find at least one of these iconic, gray, football shaped nests. By now the nests should be nearly two feet long and a foot and a half wide and be a nexus of hornet activity. Maybe our cold winter was too much for the hibernating Queen hornets? Or, maybe the wet spring and summer were too hard on the developing nests? I really miss the hornets, though!

Many people are quite nervous around these insects (and with good reason!). Bald faced hornets can deliver repeated stings loaded with powerful toxins and tend to swarm any intruder that they perceive to be a threat to their nest and colony. But, their role in nature is not to harass or sting human beings! Let’s consider the good that these insets do in both their natural ecosystems and also in human dominated ecosystems. Having a large, robust colony of these hornets nearby (but too close!) is something all of us would benefit from.

Photo by Piccolo Namek (Wikimedia Commons)

Photo by Piccolo Namek (Wikimedia Commons)

The bald-faced hornet (Dolichovespula maculata) is a large (just under an inch long), black and white colored, social wasp that is found throughout North America. It is not a true “hornet” because that term is specifically used to describe wasp species in the genus Vespa. It is, instead, a member of the “yellowjacket” group (in spite of its very un-yellowjacket-like coloration!). The bald-faced hornet has many other common names including the “white-faced hornet,” the “white-tailed hornet,” the “bald-faced yellowjacket,” the “blackjacket,” and the “bull wasp.”

Their nest is made up of woody materials that have been chewed up by the Worker hornets and pulped into a mash with their saliva. This mash is spread out to dry in layers to form the walls of the growing globe. The nest contains multiple tiers of hexagonal combs all encased in about two inches of protective paper. There are air vents in the upper portion of the nest that allow the venting of excess heat. The nest begins as a very small structure but grows through the summer as the colony gets larger and larger. All of the Workers in the nest are the sterile, female offspring of the original Queen that started the nest in the Spring. These Workers have taken over almost all of the functions of the colony leaving the Queen with the exclusive job of laying more and more eggs. The Queen’s final task of the season will be to lay eggs for fertile females (new Queens) and fertile males who will then leave the colony, mate, and establish the overwintering, fertilized Queens for next year’s cycle.

Workers are very active outside the nest during the daylight hours of the summer. At night, they are active inside the nest caring for the larvae and pupae, and repairing and expanding the structure of the nest. During the day there is a constant flow of Workers in and out of the nest. These Workers are bringing food into the nest (flower nectar, fruit pulp, tree sap, and a great variety of insects upon which they prey. Larvae are fed a rich mash of crushed up insects gathered by and fed to them by the Workers.

In the process of seeking out flower nectar, the bald-faced hornets may be contributing to the spread of pollen from flower to flower and thus may act as an agent in the reproductive cycle of many plants. The fact, though, that these wasps have very smooth bodies (as described by the “hairless” or “bald” adjectives in a number of their common names) means that very little pollen actually sticks to them. They are thought to be a much less effective pollinator species than say the much hairy honeybee or bumblebee.

The impact of these bald-faced hornets on other insect populations, though, may have great ecological and even human significances. They prey avidly on a wide range of insects but seem to be especially fond of various species of dipterans (“flies”). Deer flies and horseflies are an optimal prey size, and I have observed swarms of bald-faced hornets taking these biting dipterans in very large numbers.

Many years ago Deborah and I had a horse named Ahab. Ahab, like most horses, was really bothered by deer and horse flies in the summer. Ahab learned, though, that he could stand, motionless with his legs spread next to a line of black walnut trees (one of which had a bald faced hornet’s nest in it), and the hornets would sweep across his legs and back grabbing up the biting flies. The hornets would then fly to the rails of nearby fence and rip the flies apart in a feeding frenzy. I even watched some of the hornets hovering behind Ahab’s legs waiting in ambush for a deer fly or horse fly to blunder by. This was like a cleaning station in a coral reef in which small fish swarm over larger fish to pull off and consume their parasites! Ahab always had a bit of nervous expression on his face, though, when he was standing at attention in the hornet swarm!

So, bald faced hornets eat deer and horse flies! NO ONE likes deer or horse flies!! The enemy of our enemy, then, is our friend! If anyone sees a bald faced hornet nest, please let me know! I hope that there are enough of them out there to keep the deer flies and horse flies in check!

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