Seasonal Changes

The winter solstice is the shortest day of the year and now, it is more than three weeks behind us. With January already two weeks old, noticeable changes are taking place. Perhaps it’s part of the human condition to crave more daylight after marching headlong into the darkening days leading up to the solstice; or perhaps we really are heading toward longer days and, hopefully, friendlier weather. However humans choose to handle the seasonal changes, birds seem to take it all in stride with the realization that their time to shine is coming soon.

Already, in different habitats around the county and especially in freshwater and woodland locales, pair bonding is taking place. Early nesters like owls, eagles, and waterfowl are making their presence known by their calls, in the case of owls and eagles, and in their behavior in the case of waterfowl. Sizable flocks of waterfowl might be seen on ponds and lakes but rest assured that mate selection is already underway. With colder temperatures prevailing in mid-January, however, the business at hand is to make it through the winter.

Birds in general are to be admired by their bird watching fans for their resiliency in all types of weather. They are incredibly busy and industrious throughout the year and especially so during their courtship, breeding, and nesting periods. Rearing their young, protecting themselves in sometimes hostile environments, and keeping an eye out for predators are a full-time job. When cold weather settles in, however, those birds that don’t migrate gain even more admiration from me.

No matter the species or their methods, the key to survival in winter is to maintain proper body temperatures by finding food during the day and shelter for the long, cold nights. As long as specific food is available, birds that winter farther north will endure. If the food supply dwindles or is nonexistent, birds will take part in irregular migrations known as irruptions. A classic example of an irruptive species is the snowy owl.

With the popularity of bird feeding by humans, certain species have been known to adapt accordingly and even expand their ranges northward when dependable feeders remain filled. Locally, the increase in the number of wintering Anna’s hummingbirds is proof that this hardy hummer can handle the cold if we’re there to lend a hand. We can do our part by keeping feeders thawed and available when the cold weather dominates the day and night.

Numerous species are known to prepare for the lean winter months by stashing their food, often in crevices in the bark of living trees or in cracks in dead trees. In the case of the acorn woodpecker, families will systematically create a granary tree by pre-drilling holes in a chosen tree and then filling them with a winter supply of acorns and other nuts. Birds that have established their food caches will defend their winter food supply from other birds.

Given the longer periods of darkness in the winter months, birds have less time during the daylight hours to find food. Through adaptive evolution, the seed eating bird has a special crop in its esophagus where it can pack seeds toward the end of their daylight feeding. As the bird sleeps, these seeds are slowly digested through the long nights to provide necessary energy to maintain the bird’s metabolic rate. Other birds have the ability to slow their metabolism, while lowering their body temperature and reducing their heart rate as a means to conserve energy.

Almost as important as finding food during the day and utilizing the energy that food provides is the basic need to stay warm on bitterly cold nights. Birds in colder climates are able to fluff their feathers which provide insulation to control the loss of body heat. Equally important to staying warm is a social adaptation that some birds have adopted for survival — communal roosting. While the breeding season is often a time of intense competition and territoriality, many birds have learned to depend on each other to stay warm during cold weather. Many species utilize the concept of roosting together and they rely on each other to reduce the loss of body heat.

Locally, our Pacific wrens are well known to fashion roosting sites that are quite similar to their nests, with the exception that several fully-grown birds will basically snuggle together to stay warm during the night. I recently observed an individual wren as it gathered mouthfuls of moss and carried them to its roosting site. After several trips with more moss added to the interior of the structure, the wren then began to sing its distinctive song — as if to advertise that lodging was available for birds of their particular feather.

If you look closely at the anatomy and physiology of birds, you will see a myriad of adaptations that enable them to withstand weather extremes, and especially cold weather. On a cold day you might observe flocks of small birds constantly on the move as they seek food. From an anthropomorphic approach, just try to imagine how you might handle a bird’s life. The old bit of humor that refers to some of us as “snowbirds” is not so farfetched. If you spend time in the warmer southern states during the winter, it’s not altogether uncommon to meet folks from the northern tier states who just “can’t handle the cold anymore.” When it comes to birds of a feather, migration is a key component.

It’s endlessly fascinating from a naturalist’s point of view to observe birds and understand how complex they are throughout the year, but especially in winter when the odds of survival are stacked against them. Humans are not able to withstand the extreme variance in temperature the way that birds do. Without adding layers of clothing and relying on heat sources, we would perish in winter, or simply become as nomadic as other species that head to warmer climes during the colder months.

While the bitter, cold days of the year might be behind us, we still have a couple of months to observe birds and study their methods of dealing with the low temperatures and scarce food supplies. If you make note of all that birds have to contend with in winter, your appreciation of these avian wonders will certainly increase, as you reach for your thermos of hot coffee or antifreeze.