Social Behavior and Phenology
Date - 3/20/21
Start Time - 9:40am
End Time - 11:05
Location - Burlington Waterfront Bike Path
Temperature - ~38 deg F
~100% clear
Many of the birds we saw on the lake seemed to be engaging in feather fluffing in an attempt to keep warm in the breezy, cold air on the still partially frozen lake. Most of the time they would sit still as if in an effort to conserve energy to keep warm, but every once in a while they would rise slightly out of the water and ruffle their feathers to trap air along their body for extra insulation. In particular, I saw a Common Goldeneye floating near both other birds on the water near the beginning of the bike path, sometimes swimming near enough to partake in a “social” huddling act, likely in order to keep warm as well. These thermoregulatory behaviors are all a part of the birds’ circadian rhythm, or intrinsic cycles birds engage in on a 24hr basis. We observed the birds during the day, when thermoregulation - as well as eating and metabolic activities - were high. The Common Goldeneye would fluff, huddle, and dive under the water to feed on fish and other lake invertebrates. We weren’t able to observe any of the birds at night, but most likely the bird would reduce its metabolic and thermoregulatory activities (decreasing body temperature decreases metabolic activities) and sleep out on the water, which incidentally naturally warms in comparison to the land during the night.
Conversely, both the Herring and Ring-billed Gulls we saw spent their time catching thermals around the land and gliding over it, very likely scouting out for fish to eat. A couple other species like the Canada Geese engaged in these gliding activities around the lake as well. Common Grackles were the other major species we saw, and they spent most of their time flocking together - sometimes with Red-winged Blackbirds - between trees and telephone poles. The trees likely provided a microhabitat to keep warm, as well as a source of food to take advantage of their higher metabolic capabilities during the day. I think it’s also likely that the trees and telephone polls are places they would sleep during the night time. All locations that each of the species chose to sleep would provide them with exposure to the changing daylight throughout the year, entraining their circadian rhythms. Most of the bird species on and around the lake did not directly interact with each other, especially given that winter is ending and the need to flock together is going away, but many of them behaved in similar ways in line with their circadian rhythms, sending out calls to members of the same species as if to alert them to potential prey (this was especially done by the species of Gull). The Common Grackles responded vocally to spishing while foraging in the trees as well, becoming very attentive to that kind of sound. Spishing could mean a lot of things to different birds, but the most likely hypothesis is that it sounds like small songbirds, namely the Black-capped Chickadee, and overall just gets the bird’s attention to some kind of call or song.
Back to the Common Goldeneye, while the birds were trying to keep warm or hunting for food, the Common Goldeneye was just starting to mate as a part of its circannual cycles. As a male, it would stick its heads up and down in a bobbing motion to attract female mates. Soon, as the weather gets warmer and food becomes more abundant, the bird will arrive at the breedings grounds with his mate, who will start to incubate their eggs by the summer solstice. Their diets might change towards more insect-based diets as they become more available in the summer, as simultaneously the migratory species come back to feed on these now present insects.
While the Common Goldeneyes had some white feathers on their sides, their plumage mainly consisted of iridescent greens and browns. By contrast, the Herring and Ring-billed Gulls have an advantage during egg incubation due to their white plumages, which reflect solar radiation and help their eggs not overheat. Gulls also spend a lot of their time in flight due to the gliding abilities their high aspect ratio wings allow them to have, giving them much exposure to solar radiation in the air and making it so their white reflective plumage doesn’t need to absorb the sunlight on its own. They are able to expose different body parts to the sun very easily. Conversely, when the Common Goldeneye is out of the water and exposed to the sun, their plumage is darker, likely needed to absorb solar radiation due to the less intense exposure from the water. Their side feathers are able to be white possibility because those spend a lot of time in water, away from the sun. When the time comes to get out of the water and incubate their eggs however, their whiter plumage closer to their bottom may potentially give them the same evolutionary advantage of preventing egg-overheating just like the Gulls, providing another advantage towards successfully completing their circannual cycle.
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