The onset of winter evokes different feelings in different people. Some look forward to fall foliage and cooler temperatures. For others, it’s the arrival of hunting or trapping seasons. And for some people, it’s all about the holidays — gathering with friends and family. Many of us look forward to idyllic snow-covered mountains and farm fields.
Then there are those who dread the snowy commutes, high heating bills and the end of blue crab season.
Colder temperatures, snowpack, shorter days and reduced food sources create challenges for organisms throughout forests in the Chesapeake Bay watershed. While winters in the Bay region are relatively mild, the seasonal shift is significant enough that plants and animals here have developed adaptations that allow them to persist in an environment with ever-dwindling resources. As a result, many have developed physiological or behavioral adaptations that allow them to endure winter conditions.
Forests in the region are composed primarily of deciduous tree species — those that shed their leaves on an annual or seasonal basis. Shorter winter days mean less sunlight for plants to use for photosynthesis. So, as summer turns to fall, diminishing sunlight (and other factors) trigger the leaf-shedding process, known as abscission. Chlorophyll production decreases and the true colors of leaves, no longer masked by green, are revealed. While the mechanism that controls this process is complex, the result is a plant that has shed its energy-collecting structures to safely store resources through the darker, colder winter season.
In addition to deciduous trees, forests also have native coniferous, or “evergreen,” species. The thin needles or scales of conifers do not accumulate much snowfall and are less vulnerable to limb damage from the weight of snow. The smaller surface area of evergreen needles and leaves minimizes water loss — as does the waxy coating, or “cuticle,” of most evergreen leaves. The cuticle also makes the leaf less vulnerable to physical damage.
While many species of birds and mammals have developed physiological adaptations, they also rely on certain behaviors to survive the winter. Birds and mammals are endothermic. This means they can maintain a stable internal body temperature. This ability is quite advantageous because it allows these animals to remain active regardless of fluctuations in air temperature.
As a result, many mammals and birds stay active throughout the winter.
Maintaining this internal temperature, however, is energetically costly. Birds and mammals must continuously acquire food throughout the winter — or, alternately, have ways of reducing their metabolic rate, making food intake less critical.
The development of fur in mammals is another adaptation that allows many species to maintain consistent internal body temperatures in winter and remain active as long as food sources are available.
Many of our native songbirds migrate south for the winter. These neotropical migrants only come to Chesapeake Bay region forests to breed and raise young during the spring and summer. As their insect or nectar food sources disappear in fall and winter, they head south to find food in habitats where insects are active year-round. This strategy is known as “resource partitioning” — dividing time between two ecosystems to ensure abundant seasonal food supplies.
While the neotropicals must migrate, available food allows other birds to remain in cold climates through the winter. Seed-eating birds, like cardinals, blue jays and chickadees, are a common sight at backyard feeders during winter. Even some insect-eating birds are winter residents, having developed adaptations to obtain dormant insects through the winter.
Woodpeckers, nuthatches and brown creepers forage for insects by peeling bark, drilling holes or gleaning dormant insects from trees and snags.
The Chesapeake Bay, itself, also undergoes changes during winter. The water becomes clearer, the result of the decreasing abundance of microorganisms like phytoplankton and zooplankton. Tides are often lower because of changes in winds and the lunar cycle.
Salinity levels and temperatures fluctuate, which influences the amount of ice that forms in the Bay and surrounding tidal habitats. If conditions are right, Bay waters can freeze over. This hasn’t happened since 1977, although freezes are not so rare in the watershed’s rivers and creeks.
Plants and animals that live in Chesapeake waters must modify their behavior or develop physiological adaptations to cope with these changes. Rockfish (striped bass) may leave the Bay entirely, migrating south to spend the winter in warmer waters. Oysters use nutrient reserves that they have stored in preparation for winter. Their plumpness and nutrient stores make them highly sought-after table fare during this time. Blue crabs head for deeper water in the Lower Bay, where they burrow into the sandy substrate and remain dormant throughout the winter.
The forests, fields and estuaries of the Chesapeake watershed look and feel starkly different in winter. The lush, green deciduous forests of summer turn into drab brown, icy, snow-covered landscapes.
At first glance, it may appear that these landscapes are inhospitable and devoid of life. But the organisms living here have faced the challenge of winter for millennia, developing a diversity of adaptations to persist.
While traveling through the Bay region this winter, keep your eyes open for winter residents and try to identify the adaptations that help them survive the winter.
Jim Kauffman is a Pennsylvania forest projects coordinator for the Alliance for the Chesapeake Bay. This story originally appeared Dec. 27, 2022, on bayjournal.com.
