Field Obs4: Migration
Date: 01-April-2019
Time: 5:30-7:00PM
Location:, Woodside Natural Area, Essex, VT
Coordinates: 44.501455, -73.139805
Weather: Sunny, partly cloudy, 38°F (3°C)
Habitat: Swamp, riverside, light forest
Birds migrate in order to reach regions with high or increasing levels of food resources. Vermont is an excellent place to observe migration because many species leave the cold state in the winter to go South where more food is available. But, in the springtime, food resources increase and there is less competition, so these species migrate back to take advantage of growing insect populations and budding plants, as well as establish nest sites. Migration is a costly, so a bird must make physiological tradeoffs which has resulted in a variety of migratory distances/ patterns. Migration verses permanent resident status is a matter of life history strategies.
Permanent residents do not migrate, but instead invest energy into physiological and behavioral adaptions that allow them to survive the harsh winter conditions. For example, a Black-capped Chickadee has the ability to fluff its feathers to provide insulation, which is why a Chickadee in the winter appears larger than one in the summer. Many winter residents like the Brown Creeper, American Robin, Chickadee, and Woodpeckers also have the ability enter a state of regulated hypothermia (torpor) at night to conserve energy. Night cover is crucial, communal roosts of the American Crow and creation of protected shelters observed in the Pileated Woodpecker aid in heat retention during cold nights. Foraging poses another issue for winter residents as many insects and plants die during the cold months, but they have evolved mechanisms to overcome this. Creative foraging techniques such as the spatial memory of Woodpeckers or foraging in mixed flocks as seen with Chickadees, Sparrows, Finches, and Tufted Titmouse’s increases information sharing and caloric intake during periods of limited food availability.
Some birds forgo investing their energy into adaptions and intensified foraging efforts during winter time and migrate to more productive regions instead. There is a variety of migratory birds characterized by the distance migrated, from short to long distances. A short distance migrant observed is the Red-winged Blackbird, which is resident to Northern North America all year-round, but migrates to parts of Mexico for nonbreeding seasons and then can be seen in Northern Canada during breeding seasons. The southernmost distribution of the Blackbird is over 3,000 miles from Vermont, but considering this bird is native to almost all of the US year-round, it is unlikely any individual migrated this distance. Some medium distance migrants observed includes Song Sparrows and Eastern Phoebes, which both migrate as far south as Florida and Mexico during nonbreeding seasons up to Northern Canada during breeding seasons. The most southern distribution of the Song Sparrow is roughly 2,500 miles, but similar to the Blackbird, it has a wide American distribution so may be unlikely any individual found in VT traveled this distance. Both of these migration patterns can be characterized by the term “leapfrog migration” where Northern residents do not migrate as far south as more southern residents. The Eastern Phoebe is one of the first returning migrants to Vermont in order to breed, traveling as far as Southern Mexico over 4,250 miles away. Belted Kingfishers are characterized as long-distant migrants but can be found in central North America all year-round. During the nonbreeding season though, they can be found all the way to central American and the Caribbean and observed all the way up through Alaska in the breeding season. Although it is likely a migratory Kingfisher in Vermont came from more central North America, over 3,500 miles are between Vermont and central America. The Canada Goose has a similar resident and migratory pattern, but do not go as far south, only to northern Mexico, roughly 2,200 miles away.
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