Signs of Winter 8: Bees!

Photo by I.Tsukuba, Flickr

Photo by I.Tsukuba, Flickr

Jennifer Wood and her husband Robert Steffes keep bees. Over the years they have been not only great sources of information about these wonderful animals, but also they have kept me well supplied with the jars of honey I need to get my blood sugar elevated enough each morning to face the new day!

Jennifer responded to the “Migrate, Mutate, or Die” blog (Signs of Winter #5) by describing the adaptive strategies their bees (European honeybees, Apis melifera) employ to survive the winter. European honeybees do not hibernate, but instead stay active throughout the long, cold winter months. The honeybees cluster around the honey combs inside of their hives and shiver their flight muscles to generate heat. The temperature inside of a bee-warmed hive can reach as high as ninety degrees F (although optimal temperatures would not be nearly that warm!). The cluster of shivering bees moves up (never down!) the honey comb so that they continually encounter fresh honey to fuel their muscle contractions and heat production. These bees also rotate individuals from the very warm middle of the shivering cluster to the less warm, more stressful outer edges in order to spread the impact of the winter’s thermal stress over the entire group.

Photo Public Domain, Pixabay

Photo Public Domain, Pixabay

European honeybees, then, are primed and ready for the first hints of spring weather and are able to move right into pollen and nectar gathering as soon as temperatures and the first waves of spring flowers allow. This ability to immediately respond to the bounty of spring is a significant selective advantage for the species.

There is a downside to this overwintering strategy, though. Two years ago I wrote about the impact of a warm, late winter on honeybees that triggered their early emergence into a world in which no plants had yet flowered. These bees spent a large amount of their limited energy reserves in futile attempts to find nectar and ended up gathering almost anything that might substitute for their natural foods (one gentleman in Latrobe wrote me about bees completely cleaning out his cracked corn bird feeder!). Without extra feeding by a beekeeper, these bees would be very likely not to have sufficient food to survive the remaining cold days and nights of the winter and early spring.

The overwintering strategy of the honeybee, then, sits in a very delicate balance between great success and absolute failure! The European honeybee, though is only one type of bee out the twenty thousand known species, and many of these other types of bees have very different “solutions” to surviving the winter,

I went to a web site that listed the common insects of Pennsylvania (insectIdentification.org ) and noted the types of bees likely to be present here. The site listed the European honeybee, four species of bumble bees (Bombus spp.), and two species of carpenter bees (Xylocopa spp).

Photo by P. Vivero, Wikimedia Commons

Photo by P. Vivero, Wikimedia Commons

Bumble bees, like European honeybees, live in colonies. The sizes of these colonies, though, are quite different. A domesticated honeybee colony can contain up to eighty thousand individual bees during the peak of summer activity. A bumble bee colony, though, usually has less than fifty individuals. Toward the end of the summer new queens (fertile female bees) and fertile male bees mature in the bumble bee colony. These fertile individuals emerge and mate, and then the males die shortly thereafter. The mated queens, though, continue to feed on flower nectar and pollen and find crevices, holes, or even sheltering flowers in which they can spend the night. They steadily build up considerable body energy reserves that will see them through the long winter.

Eventually, as the summer fades and the cooler nights of autumn signal the coming winter, these queens find more protected places (often abandoned mouse nests or burrows in sandy soils) where they can hibernate. They go into a physiological state that enables them to slowly use their energy stores as they wait out the long, cold winter months. Early in the spring, these queens stir from hibernation and begin to forage for nectar and pollen among the early spring flowers. Their large body sizes and extensive coverings of hairs enable them to retain heat even in air temperatures that would seem to be too cool for insect activity. In the early spring these great, floating bees fly about close to the soil surface in their search for flowers. They must be careful, though, not to misjudge their rate of energy use or the lateness of the day or they might get caught out away from their hibernaculae and end up freezing in the cold, night air.

These bumble bee queens eventually establish their summer colony site and begin to lay eggs. The small cohort of workers that develop, then begin to assist the nurturing and survival of the colony. A bumble bee colony only lasts one season, so it is imperative that enough food resources be gathered to fuel the production of the next generation of queens.

Photo by ysmad.com, Wikimedia Commons

Photo by ysmad.com, Wikimedia Commons

Carpenter bees (Xylocopa spp.) are solitary bees (they do not form colonies although in some species the sisters and/or the daughters of a fertile female may continue to nest together in a simple social group). Adult carpenter bees drill branching cavities into wood (and can be the cause of a great deal of damage to buildings and homes), but they do not eat the wood. They discard the woody debris (or use it to make partitions inside of their woody nest) and rely on nectar and pollen for their food. Carpenter bees are important flower pollinators and many people have made the decision that the wood damage they cause to homes or barns is small price to pay for all of the essential pollinating work these bees accomplish.

Photo by ZooFari, Wikimedia Commons

Photo by ZooFari, Wikimedia Commons

Adult carpenter bees hibernate in the woody burrows in which they were born and in the spring, emerge and mate and either continue to live in those nests with their extended female family members or strike off and establish new woody burrows nearby. The male carpenter bees live solitary lives outside the nests and visit flowers to gather their individual food requirements. They do not, however, enter the nests at night or contribute to the groups’ accumulation of pollen or nectar.

Bees, then, survive winter in a variety of ways. They can be adults shivering together, waiting for warming temperatures. They can be mated, hibernating queens sleeping through the snow and cold. They can also be un-mated males and queens hibernating in their parental nest burrows.

I can’t wait to see the spring bumble bees drifting about like little zeppelins or the swarms of honeybees clustering over the first flowers of the spring! We have more winter to get through first, though! Hang in there!

Posted in Bill's Notes | Leave a comment

Signs of Winter 7: Beavers and Otters

Photo by Steve, Wikimedia Commons

Photo by Steve, Wikimedia Commons

Over the past few weeks I have had two very interesting communications from friends and colleagues here in Western Pennsylvania. One involved signs of beaver activity along the Kiski River and the other involved seeing river otters in one of the ponds at Harrison Hills Park.

The beaver report was from Carl Meyerhuber who, up until this extreme cold spell anyway, has been braving the winter weather each afternoon to do his two mile walk on the Roaring Run Trail along the north bank of the Kiski River. Carl has been seeing gnawed tree trunks and piles of chisel-shaped wood chips at spots along the trail, sure signs that the Kiski beavers are out and about.

Beavers (Castor candenesis) were once a very common component of the fauna of not only Western Pennsylvania but almost all of North America. These large, semi-aquatic rodents once had a continental population of sixty to ninety million individuals. They were, however, of great economic value to Europeans moving across the continent (and some say they were one of the main reasons that the Europeans moved across North America as quickly as they did!). By the end of the Nineteenth Century, there were only a fraction of the original continental population still alive, and there were no beavers at all remaining in Pennsylvania.

Conservation programs were established in Pennsylvania to try to re-establish beaver populations. In 1917 a pair of beavers from Wisconsin was released in the state, and between 1918 and 1925 one hundred more were brought in and released into our waterways. By 1934 the beaver populations had grown sufficiently that a regulated trapping season was established.

Photo by Hugo.arg, Wikimedia Commons

Photo by Hugo.arg, Wikimedia Commons

Beavers instinctively build dams with the small trees and branches that they cut with their powerful front incisors. They carry and float these building materials to constricted points along small streams and then mud-cement into place across the water flow. These dams create protective ponds within which the beavers can build their lodges. Lodge construction, though, seems to be a learned behavior. The “island-type” lodges set in the middle of a protective pond may have a variety of geometries

Photo by R. Stevens, cynic.org.uk

Photo by R. Stevens, cynic.org.uk

and styles but all have a number of underwater entrances and exits and at least two inner chambers (one for drying off after returning from a swim, and the other for sleeping and rearing their young).

Beavers may also build their lodges onto and into the banks of larger rivers. These “bank beavers” are the same species as the island-lodge beavers but adapt themselves to a landscape in which flat, slow flowing streams suitable for damming are not available. These river bank lodges are also constructed of mud-cemented sticks and logs, and they also have multiple below water entrances and exits and at least two internal chambers. These lodges may also extend into the soil of the river bank often in and around protective and supportive roots of large river bank trees. Both types of lodges become extremely secure in the winter as the mud holding the sticks and logs together freeze into a nearly impenetrable, concrete-like mass.

The beavers along the Kiski are “bank beavers.” The steep hillsides coming down to the river do not provide sufficiently flat expanses for beaver dams to generate protective ponds. When you drift down the Kiski in a canoe (an activity that should wait for MUCH warmer weather!) you can see these beaver lodges tucked into river bank. If you happen to be out near sunset, you may even glimpse one of the beavers as they start into their nocturnal foraging for building supplies and food.

Beavers preferentially eat water plants when they are available but survive on the inner bark of a variety of trees especially through the winter. They cache large quantities of sticks and branches under their lodges for winter consumption when conditions do not allow them to forage freely about. Poplars and aspens are preferred tree species but maples (especially red maple), birches, willows, cottonwoods, and pines are also consumed. The increased cutting activity that Carl has observed along the Roaring Run Trail is probably due to a stimulated gathering of winter food by our local beavers.

Public Domain, Wikimedia Commons

Public Domain, Wikimedia Commons

There are lots of neat details about beavers! Their front incisors continuously grow! These tree-cutting teeth are harder in the front than they are in the back and, so, wear into a beveled biting instrument that generates the very recognizably shaped wood chips around any beaver tree site. Beavers are the second largest rodent on Earth (exceeded in size only by the capybara of South America). Ten thousand years ago, though, an ancestor species of our North American beaver was the size of a black bear and weighed close

to five hundred pounds!

Photo by  D. Azovitsev, Wikimedia Commons

Photo by D. Azovitsev, Wikimedia Commons

The other semi-aquatic mammal story of the moment was actually mentioned (and pictured!) in the local newspaper a couple of weeks ago. Two river otters (Lutra canadensis) were spotted in one of the ponds up in Harrison Hills Park in northern Allegheny County.

Like the beaver, river otters were once abundant and widely distributed in Pennsylvania. But, also like the beaver, human impacts (through direct hunting and also through indirect destruction of the otters’ habitats through land clearing and stream pollution) greatly reduced the Pennsylvania otter population and functionally extirpated the river otter from almost all of the state’s waterways. In 1982 researchers from the Game Commission and Frostburg University released one hundred and fifty three wild otters that had been captured in Louisiana, Maryland, and New York into nine rivers in Central and Western Pennsylvania. In the intervening thirty-three years these otters have multiplied and spread throughout the watersheds of Pennsylvania.

The otters released into the Allegheny River (one of the nine original release sites) were undoubtedly the stock from which the Harrison Hills otters were derived. It is a very long climb up from the Allegheny to the bluffs on which Harrison Hills park sits, but the promise of fish-rich pond waters must be quite an attraction for these active predators.

In 2006 Deborah and I and Marian and Joe were canoeing on the Youghiogheny River (another release site for the otters) when we spotted an otter swimming and playing among the river rocks. She seemed as interested in us as we were in her, and the few minutes we spent observing each other was the highlight of that glorious river trip.

Beavers, otters, wild turkeys and bald eagles are all symbolic of Pennsylvania ecosystems steadily regaining some of the charismatic fauna that they have lost over centuries of ignorance and misuse. These animals make even simple walks in the woods and quiet floats down a stream potentially so much more exciting and so much more filled with adventure!

Posted in Bill's Notes | 1 Comment

Signs of Winter 6: Birds of a Feather

Photo by Frauke (Pixbay)

Photo by Frauke (Pixbay)

Winter is a great time to observe flocks of birds. Large birds, like geese for example, often fly in specific geometric formations (the “V’s”) in order for individuals in the flock to take advantage of both reduced wind resistance and also the up-wash of air that a front-flying bird generates both behind it and to its sides. Birds flying in a “V” formation beat their wings less often than a bird flying alone and also have lower heart rates. Therefore, they are able to glide more and use substantially less energy to power their flying.

Smaller birds, like blackbirds, starlings, and grackles, do not generate large enough air vortices to assist those other birds flying near them. So, there is no energetic advantage to flying in a “V.” These birds tend to fly in large, shape-changing flocks that can number from many thousands to several million individuals (one winter “blackbird” flock in the Great Dismal Swamp on the Virginia and North Carolina border was estimated to contain fifteen million birds!). Watching these swirling and flowing flocks can be a surreal experience! The coordinated twisting and turning movements that they display suggests an immense, living being rather than simply a mob-like mass.

Photo by Baker (Geograph,org.uk)

Photo by Baker (Geograph,org.uk)

Deborah and I have seen many of these “blackbird” flocks during our commuting drives back and forth from campus and our home. They rise up from corn and soybean fields or out of dense shrub fields or woodlots and move as a undulating mass over the roadways. Our car has been pelted by feces from these birds (the woodlot birds were eating wild grapes!). Thank goodness there have been frequent rain showers to clean off the car!

The emergent patterns of these small bird flock movements are generated by the expression of three very simple rules of dynamics (the work of Craig Reynolds was instrumental in bringing these internal control forces to light (see http://www.red3d.com/cwr/boids/)). The first rule is Separation: each individual in the flock tries to maintain an optimal distance from its neighbors. The second rule is Alignment: each individual steers toward the average direction their neighbor is going. The third rule is Cohesion: each individual tries to maintain a standard density of individuals in space.

These three rules are seen not only in flocks of birds but also in schools of fish, herds of mammals, and even in crowds of people! Complex group movements result as each individual in the group tries to keep their spacing, alignment, and crowd density constant.
Flocks (or schools or herds) may seem to be a huge disadvantage for a prey species seeking not to be noticed by a predator. Any predator could see or hear or smell a flock or a herd of thousands to millions of individuals! There are, though, many consequences of being in a large crowd that might lessen the impact of predation on an individual, and these benefits have undoubtedly been sorted out via natural selection and evolution to generate optimal sizes and timings of formation of these flocks, herds, or schools.

The most obvious benefit is “safety in numbers.” There are many eyes (and noses) “watching” for predators. A group of great size should always have someone watching each point in space around the flock/herd/school. Also, there are so many other individuals around for a potential predator to take! This simple risk reduction by large available numbers of prey of equal or even greater quality may be sufficient to offset the increased risk from excessive visibility . This has been referred to as the “dilution effect” in which risk decreases when it is shared over an increasing number of individuals. The famous William Hamilton (the evolutionary biologist from England and colleague of Richard Dawkins whom I talked about in a previous blog) described this dilution effect back in 1971 and used it to coin the term the “selfish herd.” He noted that the survival of individuals increases when they are in a group even though each member of that group is acting in their own self-interests (and are fervently hoping that the guy next to him becomes the predator’s mid-day snack!).

Photo by diGiusti (Wikimedia Commons)

Photo by diGiusti (Wikimedia Commons)

The flocks (or schools or herds) may also confuse predators via their mass movements or obstruct their access to specific individuals by their spacing and density. Some animals take turns rotating from the edges of their flock/herd/school into the more protected center. Many species also keep the more vulnerable individuals of their group (especially young individuals) inside these protected centers and the larger, more robust adults on the more vulnerable edges.

Predators (like many car drivers weaving around under a large, surging flock of birds) may also be confused and maybe even more than a bit intimidated by a huge, moving mass of even the most potentially vulnerable prey species.

Birds form winter flocks for other reasons, too. Finding food is major task in the winter and being in a large group of fellow food seekers makes the probability of finding food much higher. And, even though whatever food is found is then shared by many “beaks,” the net gain of food opportunities more than offsets the loss due to smaller individual portions!

Photo by Rasmussen (Wikimedia Commons)

Photo by Rasmussen (Wikimedia Commons)

Winter flocks of red-wing blackbirds, brown headed cowbirds, common grackles, and European starlings gather together in huge night roosts. The marshes of the coastal regions of mid-Atlantic states (New Jersey, Delaware, Maryland, Virginia, and North Carolina) have especially large blackbird flocks. These roosts disperse during the day into smaller cohorts that may fly as far as fifty miles seeking food.

These large blackbird flocks are also seen in Kansas shortly after the birds’ breeding season has ended. The flocks steadily increase in size with coming winter and transition from roosting in deciduous trees in the later summer and early fall to coniferous trees in the late fall and winter. They feed in the harvested grain fields of the Kansas plains during the day and hide from the prairie winds and the deep cold in the evergreen branches at night. In March the species separate and mating pairs form to get about the serious work of reproduction.

Looking out my back window, I see the falling snow and a mixed flock of chickadees, titmice, downy woodpeckers, and juncos hopping around the leaf piles and poking into the compost pile. When one finds some food item hidden in the leaf litter several others cluster around him and make short work of whatever it is. They then immediately set off looking for more. The cost of resource sharing is more than offset by the benefit of increased resource discovery. Ah. Winter!

Posted in Bill's Notes | Leave a comment

Signs of Winter 5: Migrate, Mutate, or Die

Photo by D. Sillman

Photo by D. Sillman

I have been searching around a number of “famous quotes” web sites to try to find out who first coined the phrase “migrate, mutate or die.” I wanted to use it in a winter blog with a re-phrasing into “hibernate, migrate, or die,” but even through this quote (sometimes with the added admonition “adapt” in between “mutate” and “die” (which might fit my idea for the winter blog even better!)) is widely known and used in many situations and forms, the exact author is (at least so far to me) not clear.

I remember one of my undergraduate biology professors at Texas Tech saying “migrate, mutate, or die” in his slow, drawn-out, West Texas drawl. He was discussing Natural Selection in kangaroo rats, I think. The gist of the phrase is essential Darwinism, but I cannot find these three words in “Origin of Species” or any other book by Darwin. It would have been very unlikely in any case that he would have used the term “mutate” since the “discovery” of genetics and its fusion with Darwinian selection occurred well after Darwin’s death.

I also remember a story that one of my professors at Ohio State told the small group of graduate students who had been brave enough (or possibly just sufficiently uninformed enough) to take the optional, but very demanding laboratory section that went with a two quarter long, plant physiology course. His story was a great relief from the construction of all of the elaborate apparatuses demanded by the course, and it ended with “migrate, mutate, or die” as its punchline. His story was centered on a historically notable plant ecologist at Ohio State in early Twentieth Century. This individual (whose name I have forgotten (and isn’t that the expected fate of all “famous” plant ecologists?)) took some of his graduate students out botanizing on a walk through a nearby prairie relic not realizing that one of the students the night before had planted an arctic circle tundra species out among the prairie flora. The botanist, seeing the unexpected tundra plant, stopped his on-going identification narrative and bent over to look very closely at the alien species. He pointed a long finger at the plant and said, “Migrate, mutate, or die!” and then continued on his field lecture.

Cruising around on the Internet I find this quote being used to highlight many different kinds of discussions. Real estate selling practices, funeral directors’ education programs, businesses’ competition and communication systems, the National Parks Service, some archeologists, and some on-line gamers have all used this three or four word epigrammatic phrase to focus attention on the need to change with a changing environment or run the risk of some respective professional, virtual, or biological “death.”

One document that included the quote was a transcript from an agricultural education workshop at Ohio State back in 1985. A published comment to the workshop’s keynote address attributed the quote to John Steinbeck in his great novel “The Grapes of Wrath.” That motivated me to re-read “The Grapes of Wrath,” and I can tell you that although the motivation to move or change (or die) was a large part of the novel, nowhere in the book does Steinbeck say “migrate, mutate, or die.”

It’s too great of a quote to not have an author, but whoever first said it is quite hidden!
So, let’s get back to winter and my “hibernate, migrate, adapt or die” and leave the original quote in limbo for now.

Photo by D. Sillman

Photo by D. Sillman

Hibernate: Winter shuts down most species’ food supplies. Many species respond to the anticipation of these months of crushingly limited food resources by gorging themselves on the bounty of the late summer and early fall and then falling into the slow metabolic states of torpor or true hibernation so that they can stretch these stored body resources over all of the months of winter. Bears, chipmunks, woodchucks, box turtles, snakes and many more all utilize this system with great success.

Migrate: I have frequently written about species that migrate. The robins, the grosbeaks, the tanagers, the hummingbirds and many, many more use their stored up body fat from their own summer and fall gorging to undertake long flights to tropical or southern hemispherical habitats. They spend their energy reserves on the chance that food will be waiting for them when they get across the Gulf of Mexico or down to the forests on the slopes of the Andes. Then they make the same bet three months later to cover their return north!

Photo by D. Sillman

Photo by D. Sillman

Adapt: The “adapt” part of this winter epigram really means “tough it out.” Get by on less, drive your body to eat whatever is still available in the frozen landscape, or just burn your fat reserves as slowly as you can hoping that they will keep you from freezing and also last until spring. White-tailed deer “tough it out” like this. They eat whatever they can regardless of its level of nutrition. They stuff their shrunken stomachs with chewed branches and other equally indigestible materials, and slow down their metabolic rates as much as possible to make their reserves last.

Die: The “die” option is realized by many individuals in all three of the above categories. Hibernating animals are vulnerable to predators. They also can use up their own fat reserves and end up frozen in their overwintering dens. Many individuals don’t survive the incredible physical demands of migration. It is estimated that half of the migrants leaving North America in the fall do not return in the spring. And, the species that “tough it out” regularly slip off of the razor’s edge of survival and end up frozen in the snow becoming food for a waiting host of other survivors and “adapters.”

So winter is a harsh time for wild species. I keep my bird feeders full all winter to try to help out, and I seldom chase away the squirrels or even the deer who come by regularly and gorge on the astonishingly expensive bird seed, peanuts, and shelled corn. As I watch them from my fossil fuel heated house with the promise of hot coffee and food anytime I want it (which in the winter is almost all the time!), I ignore the monetary costs and am grateful for the absence of my own ecological payment.

It’s winter!

(And, if anyone knows where “migrate, mutate, adapt or die” comes from, please let me know. I will keep looking, too!)

Posted in Bill's Notes | 3 Comments

Signs of Winter #4: Arrival of the Juncos!

Photo by Ken Thomas Wikimedia Commons

Photo by Ken Thomas Wikimedia Commons

When we think of bird migration we usually focus on those species that arrive here in the spring and then depart from here in the fall. These species are utilizing our rich, productive summers and avoiding our cold, food deprived winters. There is, though, a very interesting bird that arrives in our area in the mid- to late fall, thrives in our winters (often supported by our backyard bird feeders!), and then heads back into its northern breeding habitats in the spring. The bird is, of course, the northern junco.

I saw my first northern junco of the fall on October 30. He was poking around at the spilled sunflower seeds under my feeders and looked very much at home among the chickadees, titmice, cardinals and house finches.

The northern junco is small, dark-colored sparrow with a long list of very descriptive common names including “dark-eyed junco,” “slate-colored junco,” “snow bird,” and “winter finch.” The Northern Junco is a very common bird at almost any winter bird feeder throughout the United States. It over-winters in almost all of the lower forty-eight states (and down into northern Mexico) and has an equally broad summer/breeding range across Canada and Alaska. Breeding may also occur in the mountains of the west, throughout New England, and down the Appalachian Mountains into northern Georgia. In Pennsylvania, in addition to winter populations of “bird feeder” northern juncos, Deborah and I have observed dense, summer populations of this species in the mixed hardwood forests of the Allegheny National Forest in the northwest section of Pennsylvania.

The northern junco is five to six and a half inches long and weighs between one half and nine tenths of an ounce. Males are slightly larger than females and are more darkly colored. They have gray hoods and backs, white bellies, and dark tails with distinctive white, lateral tail feathers. They also have short, triangular beaks and dark eyes. Juveniles are brown in color and have finely streaked, white breasts.

Photo by Mdf Wikimedia Commons

Photo by Mdf Wikimedia Commons

Like most sparrows, the northern junco will eat a wide variety of foods. Their beaks are especially well adapted to cracking open even tough seeds (including sunflower seeds at bird feeders and an extensive number of wild plant (“weed”) seeds in their natural habitats). They also readily consume fruit (including wild blue berries, raspberries, and elderberries as they come into season) and many types of arthropods (including caterpillars, ants, flies, spiders, and beetles). They typically feed on the ground and move about both by walking and by hopping (a single hop can cover thirty centimeters). Natural ranges can be quite extensive (a single flock of juncos can feed in an area of ten to twelve acres), while human-modifications of their feeding ranges (i.e. bird feeding stations) can greatly reduce the size of the foraging range and overall rate of movement.

Flocks of fifteen to twenty individuals form in the autumn and winter. These flocks may include several of the sub-species of the northern junco and also several other species of sparrows and even bluebirds. These flocks gather together about thirty minutes before sunrise and disperse about forty-five minutes before sunset each day. Foraging success for each individual is significantly increased when they participate in one of the groups. An individual junco tends to stay in its foraging flock for the entire winter.

Males move into their summer breeding habitats in northern coniferous or mixed hardwood forests before females and mark off their individual breeding territories. A male will sing from the top of a tall tree to claim an area of two to three acres. They then attract the attention of the arriving females by dropping their wings and flaring their tails in order to show off their white, lateral tail feathers. Once a female accepts a male they become quite inseparable and within their territory seldom venture more the fifty feet away from each other.

The female builds the nest all on her own. The nest can be located on the ground or on low, horizontally oriented tree branches. Near human habitations juncos may also build their nests in the crawl spaces underneath buildings, inside the buildings themselves or on window ledges. The nest may be made of a variety of materials. Sometimes it is simply a gathering of pine needles and grass, sometimes it has a foundation of sticks on top of which softer materials are layered. Nests take three to seven days to build and they are seldom re-used.

Northern juncos typically have two clutches of three to five eggs each breeding season although under optimal weather conditions, a third clutch is possible. The first clutch is laid in late spring (mid-April) and the second in mid-summer (mid-July). Eggs are incubated by the female for just under two weeks. Nestlings are actively fed by both parents and are able to fledge after another two weeks or so. Fledglings stay with and are dependent upon the parents for another three weeks. Males are very aggressively territorial during this reproductive period. Both male and female, though, will very vigorously defend their nest and nestlings.

The arrival of the juncos in Western Pennsylvania has both positive and negative implications: a handsome bird has returned to grace our lawns and fields, but now we have to deal with the cold, snowy months of winter!

Posted in Bill's Notes | Leave a comment

Signs of Winter #3: Ecological Premonitions

Photo by IronChris, Wikimedia Commons

Photo by IronChris, Wikimedia Commons

There are many amazing things about nature that are both observable and explainable. One that probably isn’t, though, involves organisms like oak trees and woodpeckers and spiders forecasting, many months ahead of time, the intensity of a coming winter. For this to be observable and explainable one would have to assume that these species (and many more for that matter) somehow perceive clues in the environment that we lumbering (but sentient) bipeds do not. Take the wooly bear caterpillar for example: it is alleged that they take on a darker color if the coming winter is going to be more severe. What would be the trigger for that color change? And, maybe even more significantly, why would they do that? Even if they could perceive some clues that the coming winter was going to be cold and snowy, what advantage would it be to the caterpillar (or to the overwintering pupa of that caterpillar, actually) to have an abundance of black body hairs? There would have to be some selective advantage or the character would never have evolved!

Ten years ago I had an ecology student who wanted to study wooly bear caterpillars. His idea was to collect as many wooly bears as possible and see if their “message” was consistent across the population. He collected one hundred wooly bears over a four week period and determined the size of their black bands. He found that their winter forecast was, at best, random. The early collections seemed to lean toward a mild winter (narrower black bands) and the later collections seemed to lean toward a more severe winter (broader black bands) but the variation in each collection almost completely obscured their overall trends.

We determined two things from this wooly bear study: 1. As wooly bear caterpillars age and grow, they develop more black hairs, and 2. Selective observation of the wooly bear population (only observing a very small number of individuals at any one time) could lead you to conclude whatever you might want about the coming winter.

Selective observation may be the operational idea here!

Photo by D. Sillman

Photo by D. Sillman

There are a number of winter-predictive observations that involve things happening “earlier” than usual. There is the “early” departure of geese and ducks, the “early” migration of the monarch butterflies, and the “early” hiving up of honey bees. The quality of these observations, of course, depends upon prior knowledge of exactly when these events have happened in the past and, therefore, should be happening in the present. This data is not readily accessible.

There are also a number of observations of things being more abundant or more developed than usual. An “excess” abundance of acorns, “thicker than usual” corn husks, “more abundant than usual” late summer frogs, “thicker hair than usual” on the back of a cow’s neck, more mice (or crickets) than “usual” entering your house, and “larger than usual” spider webs being spun out in the garden. Again, the data base of “normal” or “usual” for all of these events just does not, as far as I know, exist, but if you happen to see a large spider web, or happen to hear lots of mice in your kitchen, then you might easily jump to whatever conclusions you want and then feel the need to start stocking up on canned foods!

Squirrels are also used as winter-indicators. They “frantically” gather acorns in anticipation of a coming hard winter. I have never seen a squirrel gathering acorns (or chestnuts, or hickory nuts) in anything other than a “frantic” manner. A leisurely working squirrel is very likely to become a quick lunch for a red-tailed hawk!
There were a couple of nature’s “winter predictors” that might have some validity, though. The “early arrival of snowy owls” might be indicative of the early movement of cold, polar air masses down to lower latitudes. “Foggier than usual” August and a prevalence of autumnal halos around the moon might also indicate the early arrival of colder, northern air masses which foreshadow a longer, more intense winter.

Or not.

My favorite winter-intensity myth stated that when two woodpeckers share a tree the winter will be severe. I am not sure if it matters what kind of woodpeckers might be co-habitating, but I am keeping my eyes open for that one!

Posted in Bill's Notes | Leave a comment

Signs of Winter #2: Spruce Flats Bog

Photo by D. Sillman

Photo by D. Sillman

The visual image and history of the Spruce Flats Bog are important (to the left is a summer picture of the bog). First, like the top of most of Laurel Hill, the overall topography of this site is remarkably flat. Also, like most of the top of Laurel Hill, the rock underlying this site is a thick, hard, water impermeable layer of sandstone that is covered by only a very thin layer of soil. This underlying sandstone spreads out under the Spruce Flat Bog area in a broad, shallow, saucer-shaped pan that tends to accumulate rain water and snow melt. The formation of this depression may have been caused by the weight and movement of a ridge top glacier that formed during the last Ice Age tens of thousands of years ago. The great continental ice sheets of this Ice Age terminated many miles to the north of here, but the locally cold climate they generated and the high altitude of this ridge (2720 feet) may have combined to support an isolated mass of ice. Retreat of the continental ice sheets and the warming of the climate would have melted the ridge glacier leaving behind a broad, shallow lake that then began the slow process of pond succession and transition into increasingly solid land. Simply visualized, the pond slowly filled with vegetation and sediment, and its water tolerant plants were slowly replaced by more truly terrestrial plants that began an incremental march in from the edges into the slowly solidifying center. So, this area of open water became a bog, and then a peaty-soiled wet forest, and then, as larger and larger, more rapidly transpiring trees became established, it eventually became a dry soiled forest in which the rates of water accumulation into the saucer were balanced by the outward (and upward) transpirational loss of water by the standing trees. To have looked at this site in its forest form, the potential for a bog would have been very difficult to see!

In 1908, the virgin hemlock forest on this site (and “hemlocks” were frequently mislabeled as “spruces.” Hence, the very odd name for this bog!) was cut. Following this logging, a fire burned away the slash, the re-grown shrubs and sprouts, and also much of the humus-rich upper soil layers. The site now lacked both the sponge-like organic soil materials and also its ecological “pumps” (the transpiring hemlocks). So, rainfall and snow melt once again began to accumulate as free water in the saucer shaped depression. A shallow pond formed followed by a repeat of sediment and vegetation accumulation to form a bog. The inability of trees to grow on the site and the uninformed opinion of the worthlessness of wetlands led to attempts to drain the bog. Dynamite allegedly was used to try to fracture the underlying sandstone and allow downward flow of the bog water into ground water, but the pond/bog persisted. The donation of the land to the state and the creation of the state park protected this bog (although in other state park areas other bogs have not been so fortunate).

Photo by D. Sillman

Photo by D. Sillman

In the 1950’s pitcher plants (a summer photo of these pitcher plants is to the left) were transplanted into the bog by members of the Botanical Society of Westmoreland County, and other wetland plants (like sundews) were also, undoubtedly, introduced into the site at this time. The bog contains cotton grass, cranberry, blueberry, white cedar, pitcher plants, and round-leaved sundews. Sedges grow profusely across many areas of the bog and Juneberry shrubs line the edges of the boardwalk that connects to the observation platform that was built by the Pennsylvania Conservation Corps and Youth Conservation Corps in 1995 and 1996. Conifers (including white pine, pitch pine, Norway spruce, black pine, and eastern hemlock) have been planted around the circumference of the bog forming a tall, green, wall-like palisade on the high edges of the great depressional saucer. Some of the white pines are extremely sculpted by the strong west to east prevailing winds and have grown into fantastic, “action-shaped” morphologies.

We walk down the flat, level, and evenly graveled path and in ten or fifteen minutes are standing on the boardwalk that extends out over the shallow water and wet soil. Even in the cold air of the fading afternoon I can smell the richness of the bog. The scent, a combination of rich organic muck, water, and hydrogen sulfide, pours over me and triggers a cascade of old (and very good!) memories of coastal wetlands and hours spent mucking and kayaking through them. We have the two golden retrievers on leash so that they don’t go off splashing in the bog muck. Izzy is tired and sticking with us, so we leave her off her leash. She takes a short walk into the edge of the bog but comes back to dry land quickly.

Photo by D. Sillman

Photo by D. Sillman

The brown, dry tops of cotton grass spread out over the surface of the thick, black water. Scattered cedars of various sizes and ages stand like islands in the sea of dry grass. You can picture these little cedar islands slowly expanding as the vegetative debris steadily builds up a peat layer into which more and more rooted plants can grow. We also see sphagnum moss growing in from the edges of the bog. Its slow growth and steady accumulation will be another major player in the inevitable re-transformation of this wetland into a solid, richly organic saucer of soil. Scattered in clumps of cotton grass and sphagnum are the red “pitchers” of last season’s pitcher plants. The chambers of the pitchers are designed to lure and trap insects in an enzyme rich fluid where they will be slowly digested to harvest their body nutrients.

Insectivorous plants of the bog (like the pitcher plants) are evolutionary solutions to one of the fundamental nutrient problems of wetlands specifically and wet soils in general: the lack of nitrogen. Nitrogen is a vital nutrient needed for plant growth. Nitrogen in soil is available to plants either as ammonium ions (NH4+) or as nitrate (NO3-). In very wet soils, oxygen levels are often very low due to the inability of air to penetrate into the water filled soil profile. Anaerobic bacteria in the soil then use nitrates as the final electron acceptor in their energy metabolism instead of oxygen. This bacterial generated reduction of nitrate (which is called “denitrification”) generates nitrogen gas (N2) which then leaves the soil and joins the incredibly abundant nitrogen gas reservoir in the atmosphere. So, when a soil is very wet and anaerobic, it is also almost always deficient in nitrogen. The pitcher plants and also the sundews (which we have seen here in the summer but which are not visible here on the cusp of winter) harvest nitrogen from their ensnared insects to help fuel their growth and reproductive metabolisms

After a long hike in the confines of the woods, standing on the edge of the open expanse of the bog is peaceful and welcoming. The wind, though, is picking up and the temperature is continuing to fall. The dogs lie down on the planks of the boardwalk and leave behind perfect, muddy outlines of their legs and bodies. We are going to have to find somewhere to clean these guys up before we go back to Rob and Michele’s condo in Hidden Valley! We leave the observation platform reluctantly but with even more pace to our walking speed. It is getting dark when we get back to the cars. The soft car seats and the quickly warming heater feel unbelievably good! Definitely a sign of winter!

Posted in Bill's Notes | Leave a comment

Signs of Winter #1: Hiking Wolf Rocks Trail

Photo by D. Sillman

Photo by D. Sillman

Wolf Rocks Trail is in Laurel Summit State Park about five miles east from the Grove Run Trail that we hiked last month. This area, like that around Grove Run, was extensively logged in the late nineteenth and early twentieth centuries. Most of the park roads, in fact, have been built on the rail beds of the logging railroad spurs that connected into the main line of the Pittsburgh, Westmoreland, and Somerset Railroad which ran along the present day Linn Run Road. Remnants of these old rail beds (old rail ties, gravel, etc.) can still be found along some of trails.

It is difficult to visualize the activity and human and mechanical energy that filled this area just over 100 years ago. The primal forests of hemlock, white pine, and mixed hardwoods were cut acre by acre, the downed trees were dragged to the rail sidings by horses and then hauled away to the saw mills in Ligonier. There were piles of logs everywhere. The finished lumber was shipped to Philadelphia to build houses, props were cut and sent deep into the booming coal mines, and the mining companies bought entire towns-worth of lumber. Great piles of tannin rich hemlock bark were stacked along the sidings waiting for loading and shipping to leather tanning factories. Fires from the locomotives and from the boilers in the mills were common. Much of the land was cut, then burned, and then burned again. Only a few plant species could survive the incredible ecological “filter” of this destruction and stress.

Deborah and I met Rob, Michele, Nancy and Deb down on Route 30 and then drove up the rough, dirt and gravel road to the Laurel Summit State Park picnic area. We brought Izzy for another woods adventure and Nancy and Deb brought their golden retrievers, Ripley and Maizey. The three dogs handled each other well and added a great sense of the unexpected to the hike (it is amazing what dogs find when they are in the woods and what they think to do!).

Photo by D. Sillman

Photo by D. Sillman

The first section of the Wolf Rocks Trail is a young forest dominated by red maples, sugar maples, black cherries, yellow birches and red oaks. In the summer the understory is lush and green with ferns. Today, though only a few scattered evergreen wood ferns are still green and standing. All of the other species have succumbed to the seasonal changes and are brown and dry. Witch hazel trees and saplings of the over-story trees form a middle vegetative layer along with sometimes very dense stands of the still green and vibrant mountain laurel. In the deep shade under the laurel there are small patches of snow (now THAT’s a sign of winter!).

The trees on this section of the trail are very uniform in diameter (about 12 inches) and height. This homogeneity in size is characteristic of a re-growth site that was uniformly affected by a large disturbance. The abundance of northern red oak and red maple is also consistent with a forest site that has been massively disturbed. Red oak’s ability to stump sprout and withstand fire, and red maple’s ability to rapidly reproduce and, via their abundant winged seeds (“samara”), colonize newly disturbed sites fit the site history of clear cutting and extensive ecosystem fires. The secondary trees (yellow birch, pin cherry, and black cherry) among the red oaks and red maples are also all very common “early colonizers” of sites after widespread logging and fires.

Photo by D. Sillman

Photo by D. Sillman

As we move along the trail the trees become more widely spaced. The understory between them gets a great deal of sunshine and in the summer is full of a tall and lush undergrowth. Today, great circular expanses of the frost killed ferns open up along the side of the trail. White pines (from very large trees with twenty inch trunk diameters, to saplings, to tiny seedlings) “suddenly” are growing among the maples, yellow birch, and black cherry trees. Have the pines “replaced” the red oaks? Possibly the greater distances between the individual trees in this trail section favors the sun loving pines over the more shade tolerant oaks. The pines are reproducing vigorously here. Pine needles cover the trail surface in a smooth, thick, orange carpet. The scent of the pines is incredibly pleasant.

The trail surface is wet and very broken up by rocks and roots. Its irregularity demands careful attention to each step. The trail has been very heavily used. Its surface is compacted several inches below the surrounding soil levels. Surface water from rainfall probably is directed into this lowered hollow of the trail generating an on-going erosion problem. The extensive root exposure on the trail is a direct reflection of this erosive flow of surface water. Sections of the trail have moss growing directly on the soil surface and on the exposed rocks and roots. A bare, well walked step line winds its way around and through these glowingly green surfaces

Photo by D. Sillman

Photo by D. Sillman

Catbrier (also called “greenbrier”) grows very thickly among the surrounding ferns and out into the edges of the trail. The sharp thorns cut at our pant legs as we walk past. We quickly come to the juncture of the Loop Trail, the Spruce Flats Trail and the Hobblebush Trail. The Hobblebush Trail is labeled “Expert Biking Only.” Can that trail somehow be even rougher and rockier than the trail we have been walking on?

We turn onto the Wolf Rocks Loop trail which runs first to the west and then toward the northwest along the edge of the ridge that overlooks the Linn Run Valley. Through the bare trees we get glimpses of the valley. Wolf Rocks at the end of the trail will give us an unobstructed panorama over the Linn Run and Fish Run valleys and their surrounding hillsides.

American beech dominates the first section of the Loop trail. Under the beech trees are patches of a lycopodium called “ground pine.” Over three million years ago, ancestors of these fern relatives grew as massive, tree-sized plants in the wet, coastal, swamp forests of what would become western Pennsylvania. As these behemoths died, they fell into the poorly oxygenated waters of the swamps and partially decomposed into peat. These peat layers were then sealed away from atmosphere by sediment layers laid down by the rising and falling oceans. These fossilized remains became, over time, the “fossil fuels” of coal, natural gas, and petroleum that have been and continue to be so important in Pennsylvania’s economy.

The three dogs race back and forth between their scattered people walking the trail. Maizey and Izzy come back to check on Rob and I (at the back of the group again!) and then speed on up ahead to see what Ripley might have found (often deep puddles of water and mud that are perfect spots to lie down in!). All three dogs have mud-blackened legs and feet to complement their gorgeous, golden coats. They are also having a great time!
There are more wind-thrown trees on this section of the trail. We are close to the western edge of the ridge and undoubtedly the wind exposure here is greater than at the more sheltered trailhead. The power and consistency of the wind blowing in from the west all across the Laurel Highlands represents a potential energy resource. A number of “wind farms” have been built along the ridges to try to tap into this renewable resource. But, nothing is ever free or completely harmless, and the potential impacts of these wind turbines especially on birds need to be clearly understood before we rush into their widespread construction.

The Loop rejoins the main Wolf Rocks Trail at a junction we name “Jameson’s Point.” We stop and have a quick snack and break. The trail then follows a broad, flat, well walked path out to the rocky overlook. The rocks themselves are great blocks of sandstone that have begun to crack and shift away from the mass of the ridge. Ice wedging, root intrusion, and the slow, steady pull of gravity (not to mention the weights and vibrations of quite a few hiking boots) will slowly power the separation of these rocks from the ridge top. Someday, the rocks will break away and tumble down the slope to make a “rock city” on some level section of the hillside.

Photo by D. Sillman

Photo by D. Sillman

We put the dogs on their leashes as we approached the rocks and promontory. We don’t want them stumbling off of the rocks or sliding down the steep cliff face. On past visits to these rocks we have seen large rattlesnakes among the shrubby vegetation. In fact, in 2006 we saw the biggest timber rattlesnake I have ever seen in Pennsylvania coiled up under a mountain laurel bush. His warning rattle was deep and loud! It was difficult to determine his exact length but he was in a foot diameter coiled mass, repeatedly wound around himself, and his body was the diameter of my forearm. Even allowing for adrenaline induced visual exaggerations, he was impressive! But today, in early November, there are no active rattlesnakes so we climb about and put our hands and feet into crevices that we would surely avoid in warmer weather.

The sun is starting to drop down in the western sky and the temperatures are steadily falling. We zip up our coats more tightly and speed up our pace a bit as we walk the main trail back to the parking area. Red and sugar maples, red oak, black cherry, and sassafras dominate the forest. Cat brier and mountain laurel fill in the understory along with an impressive number of mostly red maple seedlings. There is a park-like feeling to the forest: widely spread trees surrounded by a uniform understory. Could the rocky soil be one of the causes of the great spaces between the trees? Along one long section of the trail the path was elevated on packed up soil and crossed several covered cross-logs that spanned sections of boggy soil that was loaded with sphagnum moss. Possibly this was an extension of the nearby Spruce Flats Bog.

We get back to the cars after a little more than three hours of hiking. We are tired, a bit footsore, and cold but decide that we need to keep going so that we can see the Spruce Flats Bog before the sun completely sets.
(continued next week!)

Posted in Bill's Notes | Leave a comment

Signs of Fall 11: Robins and Ring-necked Snakes

Photo by D. Sillman

Photo by D. Sillman

I hadn’t seen (or heard) a robin (good old Turdus migratorius) in several weeks. Over the early weeks of the Fall small flocks had passed over our hilltop on their south and west trajectories. Every once and a while one or two had dropped down from their flight paths and paused here in Apollo to snack on some local earthworms or grab some wild grapes, but there had been no robins for quite a while. It was exciting, then, last Saturday morning when I went out early to fill the front yard bird feeders and was greeted by a loud, unmistakably “robin” extended cackle. It took me several minutes to find the singer: it was a dark black robin with a bright red breast perched up on the almost leafless branches of my red maple tree. A Newfoundland robin!!

Robins spend their springs and summers as mated pairs with very loose flock connections. In the fall and winter, though, they form large flocks that travel locally from one feeding area to another. Many of these flocks even migrate long distances to spend the winter in milder, southern climes. The driving force that moves these flocks is food. In the late summer robins “disappear” from many places here in Western Pennsylvania much to the concern of local bird watchers. These “gone robins,” though, have just vacated one spot to concentrate themselves in some other locale that has more abundant food supplies. People living in these robin-blessed sites wonder at the population explosion going on around them and are concerned by the out-of-control expressions of nature. Deborah and I were driving out in Burrell Township (Armstrong County, PA) late one July a few years ago and were stunned by the thousands and thousands of robins that were hopping around on the ground and perching on almost every free tree branch. The noise they made and the mess they created on every surface with their droppings (is this where their genus name comes from?) were astounding!

It is interesting that although the American robin is one of the most common, most abundant, and most recognized birds in North America its migration patterns are not at all well described. I think that the lack of patterns in their year to year migrations at the onset of winter and then at the advent of spring is due to their dependence not on temperature or weather patterns or geomagnetic sensory systems (things that would be predictable and generate fairly hardwired responses) but instead it is because they follow their food supplies wherever the vagaries of the previous season generate scattered spots of abundance.

American robins are found all over North America. They summer and breed in Canada and Alaska, spend the entire year and breed all across the continental United States, and winter down to southern Mexico and even just a little further south into Central America. The mid-February “arrival” of the robins here in Western Pennsylvania is major sign of spring but probably represents just the ebb and flow of locally overwintering populations transiently leaving their sheltered (and probably fruit filled!) hollows and valleys on short forays out into suburban landscapes to look for earthworms in thawing acres of yard grasses.

I am familiar with three of the seven subspecies of T. migratorius. The subspecies here in Western Pennsylvania is the classic (or “nominative”) form of the American robin. It is widely distributed across the northern United States and Canada all the way north to the very edge of the tundra. The “Newfoundland” subspecies (whom I think that I saw up in my tree last Saturday) has darker black back feathers and redder breast feathers than its nominative subspecies. It may also be (in my opinion anyway, although I could find no reference that agrees with this!) slightly larger than our “usual,” nominative robin. These “Newfoundland” robins may simply represent a color form that is out on one extreme of the species normal color distribution. “Black backed” robins can be seen almost any time of year through the bird’s North American distribution. But this dark, intense coloration does seem to predominate in the robins from Canada’s northeastern coast. The third subspecies is the “Oklahoma” robin. This robin’s back feathers are more gray than black, and it has a pale, reddish orange breast. They look dusty and dry (as is fitting the dust-bowl center of their distribution). When I visited my parents in Tulsa these are the robins I would watch ranging across the suburban lawn-scape as they searched in the coarse grasses for worms.

Photo by David Hoffman (Flickr)

Photo by David Hoffman (Flickr)

Changing the subject to snakes! My good friend Carl Meyerhuber called me last weekend to report a sighting down on the Roaring Run Trail. Near the Canal Street parking lot Carl spotted an immature ring-necked snake crawling slowly across the trail. It seems very late (and it has been very cold!) for these delicate snakes to be out and about. It was a good thing that Carl was there to make sure that this slowly crawling, well chilled young snake made it all the way across the trail!  Last summer I wrote about ring-necked snakes and said that in spite of the DER’s declaration that they are one of the five most common snakes in Pennsylvania I had never seen one. They are shy and nocturnal and hard to find. I hope that this little immature ring-neck found a suitable place to hibernate down in the vegetation beside the Kiski River. I will look around for him next summer!

Posted in Bill's Notes | Leave a comment

Signs of Fall #10: Where do the frogs go in winter?

Northern green frog (photo by Contrbaroness. Wikimedia Commons)

Northern green frog (photo by Contrbaroness. Wikimedia Commons)

A few weeks ago Jane Viti, one of my teaching colleagues, asked me what was going to happen to the two frogs that had been living in her small, backyard pond all summer. As we talked about her frogs’ appearance, behavior, and songs I decided that they must be Northern green frogs (Lithobates clamitans melanota), and since her pond is quite shallow and expected to freeze solid over the winter, and also because it is surrounded by a very dense growth of myrtle, I speculated that the green frogs (which can either hibernate underwater or underground) would leave the soon-to-be-solid pond and dig a hibernaculum in the soil under the protective cover of the myrtle. But where these frogs sit out the winter was just the beginning of this story. Frogs are ectothermic (they rely on the heat of their environment for their body heat) and would seem quite vulnerable to freezing solid in the very cold winters of Western Pennsylvania even if they were underground or underwater. How could they survive this extreme thermal trauma?

In my Cell Biology class I talk about changes that can be seen in cell membranes in both amphibians (like the green frog) and reptiles (like turtles and snakes) as seasonal temperatures begin to fall. An enzyme is stimulated that begins to add double bonds to the fatty acids of the cell membrane phospholipids. This “desaturase” enzyme makes the altered fatty acids more crooked and thus less able to stick together. This reduces the freezing point (which usually referred to as the “melting point” for some reason) of the cellular membrane and keeps the membrane “fluid” and functional at lower and lower temperatures. Also, amphibians add cholesterol to their cell membranes, and these steroids further keep the fatty acids from clumping together even at decreasing temperatures.

These changes help to keep our frog active at temperatures that are lower than optimal, but eventually temperatures start to approach the freezing point of water, and the frog is at risk of cell and tissue damage from the freezing of the water in its blood and cytoplasm.

Frostbite on human toes (Photo by Dr. S Falz-Colleque Wikimedia Commons)

Frostbite on human toes (Photo by Dr. S Falz-Colleque Wikimedia Commons)

Let’s take a second and think about people. When skin is exposed too long to freezing temperatures cells are destroyed and “frostbite” occurs. Why do the cells die? First, the blood flow into the cold body part is curtailed in order to prevent excessive body heat loss (humans are endothermic organisms who use the heat from their metabolic activities to generate their body heat and there is only so much heat energy to go around!). The lack of blood flow into the tissue means that oxygen is no longer being delivered and cell death from lack of oxygen may occur. Also, and maybe of a more immediate concern, the lack of warm blood entering the tissue means that the fluids in the tissue and in its cells may start to freeze. Usually the interstitial fluid around the cells freezes first and these ice crystals actually start pulling water out of the inside of the cells. For a while this dehydration event may actually hold off cytoplasmic freezing, but eventually the cell will be irreversibly damaged (i.e. “killed”) by either excessive dehydration or by the inevitable freezing of its cytoplasm.

But, let’s get back to our frogs: before the frogs are exposed to freezing temperatures they undergo many physiological changes in addition to the cell membrane changes I listed above. Their livers start synthesizing and releasing large quantities of glucose (“sugar”) into their blood streams. These sugars are absorbed by the cells of the body causing the cytoplasm to become thick and syrupy and increasingly hypertonic to the surrouding interstitial fluids. Also the frog releases special proteins called Protein Ice Nucleases (or “PIN’s”) into their blood stream. These proteins will stimulate freezing of the water in the blood stream which will then inhibit the potentially lethal freezing of the water of the cytoplasm inside the cells! When the frogs are finally exposed to truly freezing temperatures the skin and then the rest of the body freezes solid (they are like little rock statues of frogs!), but the freezing is primarily confined to the blood and to fluids around the cells! The forming ice crystals in the interstitial fluid draw water out of the cells (just like in human frostbite) but the high levels of sugar inside the cells not only act as a natural antifreeze for the cell but also hang onto enough water so that the cells don’t dehydrate to the point of death!

Gray tree frog (photo by L.A.Dawson. Wikimedia Commons)

Gray tree frog (photo by L.A.Dawson. Wikimedia Commons)

Terrestrial frogs (like the American toad (Bufo americanus), the wood frog (Rana sylvatica), the spring peeper (Hyla crucifer), the gray tree frog (Hyla versicolor) and the northern green frog when it decides to hibernate on land) basically let themselves freeze solid in their soil hideouts. Wood frogs and tree frogs don’t even go down into the soil but just bury themselves in piles of leaves and ride out the months of freezing temperatures. During warm spells these terrestrial hibernators may even thaw out and move around, but they will typically then re-freeze and settle back into their winter slumbers. I noted in several spring and summer blogs this year the very large number of gray wood frogs in the trees around my field and yard. I wonder if all of the leaves that I have been letting pile up under my trees (because of my selective leaf-raking policies) provided these great creatures with sufficient winter habitat to favor the growth of their population?

Aquatic frogs (like the leopard frog (Rana pipens) and the American bullfrog (Lithobates catesbeianus) and the northern green frog when it decides to overwinter in a body of water) spend the winter if not frozen then nearly so in the still liquid environment of their ponds or pools. They do not bury themselves in the muds of these systems because they must continue to pick up oxygen from the surrounding water through their skin. Sometimes they sink to the bottom of their pools or ponds (they are quite solid and have no air in their lungs) but they must keep contact with the oxygen-rich water in order to survive. They also may swim about a bit when they warm up during lulls in the winter cold. Aquatic frogs can survive freezing solid in ice, but I don’t know how long they can live that way. The lack of oxygen would surely be fatal if the ice-encasement persisted for too many weeks.

So, on the next cold Fall night as you sit in your warm house wrapped in an afghan or a sweater, give a thought to the little frozen frogs outside who are waiting for their personal Spring thaws to come.

Posted in Bill's Notes | Leave a comment