Field Observation 4: Migration
Date: April 3, 2019
Location: Centennial Woods
Time: 7:50am - 9:20am
Weather: 37°F and Partly Cloudy
During my walk through Centennial Woods, the majority of the birds that I spotted were not migrants. The Dark-eyed Junco, Black-capped Chickadee, American Crow, and White-breasted Nuthatch were all present during the winter season. It is possible that these birds do not expend energy to migrate because they are able to survive the winter conditions as long as food is available. Migration may increase the risks of survival because multiple things could occur during the migration. These individuals are forced to adapt to the harsh winter season while other individuals migrate to warmer areas that have more food resources. I did notice that these birds were more active than other times that I have observed them during the winter season. The American Crow was flying around with something in its beak and the Black-capped Chickadee was very vocal. Some individuals were starting mating displays and songs. These individuals that stay in Vermont during the winter have to regulate their body temperatures. For instance, they can utilize facultative hypothermia. Black-capped Chickadee uses this process to tolerate colder temperatures by burning less calories. Torpor is another adaptation to survive winter. Birds also have morphological adaptations, such as darker plumage for solar retention and counter current exchange to regulate blood temperature.
Throughout the walk I heard the Song Sparrow. Song Sparrows are known to migrate during the spring. The spring migration may have been triggered by longer days and increasing temperatures. The Song Sparrow was also relatively responsive to "phising". Arriving in early April allows the Song Sparrow to establish its territory before other migrants arrive. However, they also have to deal with residual winter conditions that later migrants do not have to endure. The medium-distance migrant probably came from southern areas of the United States, such as South Carolina which about 900 miles away.
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