Field Observation 4: Migration

Date: April 6th, 2019
Time: 2:30 PM
Weather: 7 °C, cloudy. Winds: SW, 5 mph.
Location: Casavant Natural Area, Winooski, VT
Habitat: Deciduous forest along a river. Grassy, sandy areas along river edge. Dense forest cover.
Some bird species may migrate south in the winter, chasing quality food and habitat that they can no longer find in their breeding grounds during the colder and darker months of the year. Other species can tough it out and stay in place by utilizing specialized behavioral and physiological adaptations. For example, one of the species that I observed today, the Hairy Woodpecker, is a persistent year-round resident bird species in Vermont. Woodpeckers are expert climbers, with strong feet and claws that allow it to cling to tree trunks, positioning itself so that it can be shielded from the winter winds. The Hairy Woodpecker is a widespread generalist, able to survive in a wide variety of habitats with an assortment of foods. This helps them remain in place all year, because they do not rely on one seasonal food source. They can adapt to changes in food and habitat availability, so long as they can find dead trees for excavating. Hairy Woodpeckers can re-decorate their habitat by drumming holes into trees, which they use for nesting and for shelter. Other year-round residents, such as the Black-capped Chickadee and White-breasted Nuthatch, will also utilize the holes that woodpeckers create for shelter and warmth in the winter months. Black-capped Chickadees are also able to stay warm by the physiological process of facultative hypothermia, in which their body temperature is actively down-regulated to a specific level to reduce heat loss and save energy to help them survive the cold.
One species that may be somewhat less abundant in Burlington these days is the Canada Goose. Geese that breed in the High Arctic fly south throughout the United States for the winter, but they are returning to their breeding grounds far north in Canada and Alaska around this time of year. However, in recent years, as lawns have proliferated, these grassland-adapted geese may stay put in urban and suburban areas year-round. There are multiple triggers for a bird’s migration to and from its breeding grounds. The most prominent factors influencing migration are resource availability (food, nesting locations) and changes in day length. The Canada Goose is migrating northward this time of year to take advantage of budding plants and an abundance of nesting locations in the far north. It’s also possible that there is a genetic drive for migration in some bird species, described as “migratory restlessness.” This is a type of impatient, anxious locomotor activity observed just before the onset of a migration, indicative of an urge to migrate.

Publicado el abril 7, 2019 07:10 TARDE por jessharkness2