Sam Christopher, Field Observation 4: Migration

On April 1, 2019, I went birding from 5:30 to 7:00 pm on the Island Line Trail near Burlington, Vermont. This habitat consisted of both a forested bike path and an open bike path surrounded by water. The weather during this trip started as 38 °F with cloud cover of 30% and ended with a temperature of 35 °F with a cloud cover of 30%.
The first part of my walk started in a closed woodland. Within this area I observed American Robins on the ground foraging and moving between the trees, Black-capped Chickadees flying amongst branches, and heard the call of a Tufted Titmouse. Moving further down the bike path the closed woodland turned into more open marshland with tall grasses. Calls of Red-winged Blackbirds were evident and coming from all directions. There were approximately seven or eight individuals. The bike path soon turned into the Island Line Trail which has a few trees on the edges of the trail, but is surrounded by Lake Champlain on either side. Most of the water surrounding this portion of the causeway was frozen solid so no water birds were seen in the lake. The species observed in this habitat drastically changed compared to the birds in the forested and marshy areas. I followed one crow down the path as it moved from tree to tree every time I caught up to it. Ring-billed Gulls were constantly flying overhead mainly from east to west towards the Adirondacks. A group of mallards was also spotted flying north along the path. The most intriguing sight was of two Bald Eagles sitting on the ice approximately 40 meters away from the path. Both individuals were motionless on the ice for about 10 minutes and then the pair flew across the path to one of the nearby islands to rest in a tree.
The species observed were a mixture of year-round residents and facultative migrants to Vermont. Migration is energy costly and if birds can survive without migration it may be to their advantage to save energy and remain in the same location all year. The year-round residents according to All About Birds included Black-capped Chickadees, American Crow, Tufted Titmouse, Bald Eagle, American Robin, European Starling, and Canada Goose. These species are able to survive the harsh Vermont winter without needing to migrate to a different climate. This could be due to physiological, behavioral, or morphological characteristics. Physiological adaptations may include the ability to undergo torpor which would allow these species to burn fewer calories during thermoregulation. Their ability to lower their body temperature and decrease their oxygen consumption daily depending on the external temperature gives certain species an advantage when trying to save energy in the winter. A few behavioral adaptations that individuals may undergo include huddling with other conspecifics to minimize heat loss, utilizing sunny conditions to undergo activities such as foraging, or choosing a strategic cavity or other type of shelter that will maximize protection from brutal weather conditions. Perhaps another behavioral characteristic would be food choice. Generalists might be more successful in winter conditions since they are able to eat multiple food sources. For example, Black-capped Chickadees eat seeds, insects, berries, and invertebrates. They have a lot of choice in food and are therefore able to eat whatever is available to them. Specialists may have a tougher time surviving winter conditions. If their food source becomes unavailable then they may not be able to adapt to a new type of food. Morphologically these species may have adaptations that allow them to withstand harsh winters. For example, they may have an increased amount of down feathers or a rounder body that maximizes heat retention.
Both Red-winged Blackbirds and Mallards are facultative migrants. These species don’t stay in Burlington year-round. Red-winged Blackbirds typically move south to central and southern United States. Mallards also exhibit this pattern and fly south. The Mississippi Alluvial Valley is one possible wintering location for Mallards since it has water that doesn’t freeze over which allows for Mallards to have access to their preferred habitat and food supply. These species travel back north to areas like Burlington in the spring when it is time for them to breed. Possibly visual cues such as amount of daylight or morphological cues such as hormones trigger these species’ migration back to their breeding grounds. By this time, breeding habitats should be more hospitable to these species comparatively to winter conditions. Increased food sources should be available and weather conditions are typically milder around this time.
Mini-Activity:
Red-winged Blackbirds:
-Spend the winter in central to southern United States
-Traveled: 250-1,300 miles
Mallards:
-Spend the winter in the Mississippi Alluvial Valley
-Traveled: 1,252 miles
Total by Migrants: 1,502- 2,552 miles

Publicado el abril 7, 2019 09:26 TARDE por sgchrist