Migration Observations from East Montpelier, Vermont

I went for a bird walk on Tuesday, April 7. This walk began at 7:35 a.m. and lasted until 9:15 a.m. It was a cool morning. At the beginning of the walk it was 35 degrees Fahrenheit but by the end of the walk it had warmed up to the upper 30s to low 40s. It was a brilliantly sunny and still morning. There were no clouds out. Frost layered the grass and leaves. I began my walk by following the edge of my lawn which abuts a mixed forest habitat, composed of primarily Scotch Pines, Maples, Poplars, and Beach trees. The forest in not incredibly dense, especially without the undergrowth and leave on the trees. This allows for sunlight and wind to reach even the more inner areas of the forest. Within this edge habitat I observed many Black-capped Chickadees, American Crows, and Blue Jays. On the second part of my walk I traveled through thicker coniferous forests. It was darker, cooler, and moister in here. This forest section had less edge habitat, so it was likely inhabited by species that are less edge sensitive. While in this forest, I heard many Song Sparrows and Northern Cardinals. I circled back around and made my way into the thinner deciduous forest and then out into the open grassland habitat. Here is heard the Eastern Phoebe and was able to observe many American Robins who were both foraging or were up in the trees on the edge of the grass projecting their songs out to the world. This circuitous route took me through a variety of habitats which allowed me to be exposed to species that may have different habitat preferences or needs.

Black-capped Chickadees, American Crows, and Blue Jays can bee seen here year round. There are a few adaptations that allow the to survive through the winters here. Firstly, these birds appear to have generalist diets, meaning that they can forage for a variety of seeds, plant matter, and maybe even insects come summer. This would not be possible for a bird that is solely reliant on an insect diet because insects cannot survive the cold temperatures associated with Vermont winters. To add, I know that the crows are able to scavenge, which broadens their food options even more. Throughout the winter I see the crows feasting from the compost, which is also located on the edge of the forest. Secondly, these birds have behavioral strategies that they employ during the winter to stay warm. For example, on really cold days, I never see these birds out. It is likely that they are sheltered away as to maintain their body temperatures. They will only come out when it is warmer, or their need for food outweighs the energetically expensive task of foraging in a cold climate where food may be hidden by snow, difficult to get to, or simply scarce. These species may employ strategies including huddling to as to generate a greater collective heat and shield part of their body from the elements. It is likely that their steady state metabolism and body temperature is lower, meaning that they are less responsive if a predator attacks, but they have to expend less energy to maintain homeostasis. Lastly, these birds have thick down below their contour feathers which provides insulation. They can puff out their feathers so as to increase the insulative abilities.

Contrastingly, Eastern Phoebes are an obligate migrants in this region. They are insectivores, and therefore must migrate to wintering grounds where they will have access to food resources that are not available during Vermont winters. The Eastern Phoebe has returned because the photoperiod is increasing now which induces hormonal responses, driving them to become restless, eat a lot, and eventually make the trip back up from Mexico or the Southern US to the Northeast or Canada. This is also driven by overall climate patterns, and the knowledge that the habitat will bring with it open nesting sites, hopefully few predators given the time of the year, and replenishing food stores. On a smaller scale, Phoebes are receiving cues such as aggression among neighbors, new vegetation, ritualized displays, and increasing temperatures which fuel the urge to migrate. The fact that this Phoebe has arrived to Vermont in early April brings both costs and benefits. On the one hand, few birds have returned, meaning that this Phoebe has the best choice of nesting sites, territories, and resources such as food. However, the weather has been variable here. It is due to snow later this week, followed rain and cool temperatures. This could be energetically expensive for the Phoebe who has just arrived after a long journey and who body is already likely depleted from that trip. To add, although there is some vegetation returning, there is very little green habitat to provide both protection or food resources.

In terms of the mini activity, I have added up the migration miles associated with an Eastern Phoebe, an American Robin that is a facultative migrant (stopping here on its way through to Canada), and a Mallard, which is another facultative migrant that nests up in Canada, Alaska, and even parts of Greenland. The Eastern Phoebe travels 2735 miles, the American Robin travels 2596 miles, and the Mallard travels 1452 miles for a total of 6783 miles between these three individuals. However, this may not be their final destination and could have many miles still ahead of them as they continue their journey north.

Publicado el abril 8, 2020 06:28 TARDE por emerrylees