#bioPGH: Winter Ecology
A resource of Biophilia: Pittsburgh, #bioPGH is a weekly blog and social media series that aims to encourage both children and adults to reconnect with nature and enjoy what each of our distinctive seasons has to offer.
Imagine for a moment that you’re a black-capped chickadee on a summer day; flittering here and there in a brushy thicket with a number of other chickadees. You keep one eye on the hawk in sky, but you all are engaged in the endless pursuit of spiders and various insects for a nutritious meal. Now, still as a chickadee, imagine that the season has turned. Snow covers the ground, and those insects of the summer are in short supply, so instead you forage for remaining plant materials and pick at carcasses for fat and protein. Hawks are still a concern as winter adds a note of desperation to their efforts, but you have a clearer view of them without foliage. At night, to manage your energy use, you purposely allow yourself to fall into a controlled hypothermia, your body temperature dropping by 15°F. Winter is a different world for you!
Now imagine that you’re a mighty oak tree. Centuries older than your oldest human neighbors, who are currently adding scarves and hats to their daily outfits. You have already dropped your leaves for the year, and you further respond to the chill by adding sugars to your living cells as a natural anti-freeze. With the ground now frozen, water is difficult to come by, and the freezing cold could damage any newly grown tissue in roots or shoots. You respond by halting new growth until warm temperatures return. In the meantime, your branches are still a playground and a residential high-rise for the many birds who do not fly south in the winter.
Both of these scenarios are examples of winter ecology. Ecology is the study of interactions and relationships between living things and their environment. Predator-prey interactions, flowering time, migration, water quality, feeding habits, burrow-digging—all of these different facets are encompassed within ecology. It follows, then, that winter ecology looks at all of these interactions and relationships specifically during winter time. Since we are rapidly approaching the official start of winter, marked by the winter solstice on Dec. 21, let’s take a broad look at winter ecology in our area—what do our living neighbors do in the winter?
Whether we’re looking at birds, mammals, arthropods, amphibians, or any other kind of animal, there are three broad ways that wildlife can respond to winter: hibernate, migrate, or just tolerate the cold. Winter ecology looks at which of these solutions an animal chooses, why they opt for that response, and how they specifically carry out their survival strategy.
In Western PA, the animals we most expect to see migrating are birds. Not all do, of course, and it’s important to note migration is a response to a seasonal change in resource availability or a change in resource need—not just cold weather. Species that exclusively prefer fruits, nectar, or (some) insects, for example, will have much lower success in a wintry Western Pennsylvania than species who are open to a wide variety of food sources.
Of the animals who stay in PA throughout the winter months, some hibernate. Many amphibians, for example, will burrow into leaf litter, snuggle into cracks and crevices of wood, head underground, or settle at the bottom of ponds to hibernate. Some even produce a sugary “anti-freeze” that helps keep their bodies safe from ice crystallization. Other hibernating animals, like bears or groundhogs, vary in how deeply they “sleep,” but the idea is to dramatically lower metabolism through the months of low resource availability.
On the other hand, many animals simply have to “tolerate” the cold. Like our chickadee from the beginning, winter ecology often includes dietary changes dependent on food availability, and it can also include behavioral changes as many animals will lower their activity level to reduce energy loss. For aquatic animals like fish, overwintering can include a “resting” state that involves a slow-down of physiological processes, which isn’t quite hibernation, but serves a similar energy-saving goal (there are a few known examples of fish that hibernate or estivate, but not our local fish).
For plants, winter ecology includes studying how a plant either survives the winter or ensures that the next generation will live on. Annuals and biennials, for example, only primarily live one or two years, respectively, but when they die in winter, they leave their seeds behind for the next growing season. Plants such as the oak tree mentioned in the beginning survive harsh winter conditions a combination of adaptations, including dormancy. If you remember from our chat last year, though, there are three different “types” of dormancy that include endodormancy, ecodormancy, and paradormancy. Each of these involves different environmental cues and different molecular processes.
Fungi and Soil Microbes
While the fruiting bodies of mushrooms may be absent in winter, fungi and soil bacteria are still active in freezing temperatures! These microbes are important for the breakdown of organic materials, and even though decomposition rates slow in the winter, the microbes are still working in the ground. Some studies have noted that winter can change the ratio of fungi to bacteria in the soil and that the diversity of soil microbes can change seasonally, but that’s just a part of winter ecology!
Water and Ice
Ecology includes the non-living components of an environment, and a major point in winter ecology is that ice floats. Most other elements and compounds are more dense as a solid than they are as a liquid. The fact that water is an exception (a quirk of hydrogen bonds) is an ecological life-saver! If ice froze at the bottom of ponds and lakes, the fish and other creatures in the body of water wouldn’t stand a chance against freezing in winter. Since it freezes on the top, though, aquatic inhabitants are able to live safely under the ice.
Our Own Winter Ecology
You don’t have to imagine you’re a chickadee or a tree anymore. How does our own behavior and diet change in the winter versus the summer? Do you prefer different foods during cold or warm weather? Do you have a tendency to wear cozy blankets as a fashion statement? (I’m guilty of this trend.) What other activities change in the winter versus the summer? It’s fascinating to think of our own human ecology!
Connecting to the Outdoors Tip: You can study winter ecology around your own home! Ecology, like other sciences, simply requires asking a question and then answering that question by collecting data. For example, do you have a bird feeder? Set aside a recurring time block once a week and monitor what birds are at your feeder. Make a list of the species you see and make a tally mark for each bird of that species who stops by. Continue this into the summer – does the composition of feeder visitors change between winter and summer?
Continue the Conversation: Share your nature discoveries with our community by posting to Twitter and Instagram with hashtag #bioPGH, and R.S.V.P. to attend our next Biophilia: Pittsburgh meeting.
Select Photos: Wikimedia users Vaidor Otsar CC-BY-SA-3.0 and USFWS CC-BY-2.0