Field Observation 4: Migration
I went to Mckenzie Park in Burlington, VT on Sat., April 6, 2019. I arrived at about 7:45 AM and the sky was slightly overcast. The temperature was ~40 degrees Fahrenheit. The observations mentioned in this journal post are birds that I was able to see/hear walking along Calkin's Path in the Intervale, towards Mckenzie Park.
Most of the birds that I spotted were resident species that are known to be year-long residents of Vermont such as the Downy Woodpecker, Pileated Woodpecker, Black-Capped Chickadee, Northern Cardinal, Tufted Titmouse, American Robin, American Crow, and the American Goldfinch. In order to survive Vermont's notably harsh winters, these birds must have behavioral and physical adaptations that allow them to do so. In fact, most of the birds that are year-long residents of Vermont are habitat generalists. Being a generalist means they have more options when food is scarce and don't necessarily need to migrate to find the specific resources they need. For example, both the Downy Woodpecker and the Pileated Woodpecker are habitat generalists since they are able to eat insects, seeds, and berries. Generalists may also make food stashes when weather is more favorable so that they can turn to them when resources are harder to come by during the winter. Black-capped Chickadees are known to create food stashes for the wintertime. There are also some physical adaptations that allow for better winter advantages. For example, woodpeckers' beaks also allow them to hollow out effective tree cavities for them to be protected from the harsh cold. Chickadees also have denser winter down coats to allow them to maintain their body temperature even with their small body sizes that are more susceptible to heat loss. To survive during the cooler nights some year-round birds, like the Chickadee, can actually lower their body temperatures where they go into a state of regulated hypothermia. Birds can also work together behaviorally to survive Vermont winters. For example, Song Sparrows will huddle together in groups to keep warm. On my short hike, I saw over 10 House Sparrows. These birds could likely use each other for warmth. I also saw a group of 3 Brown-headed Cowbirds that were flying around together from tree to tree. Cowbirds are known to join huge roosts with other blackbirds species to bear colder weather.
I was also able to spot some facultative & obligate migrants. I spotted two Common Mergansers taking off from the Winooski River along the trail path. These birds are mostly obligate species although some have been seen year-round in Burlington VT which would possibly make them facultative. Interior Mergansers (not on the coast) tend to migrate further than those on the coast. In the winter they tend to fly South to slightly warmer weather. Mergansers need open water so they must migrate to locations that have that available to them. So, if all of Vermont's bodies of water are frozen over they must migrate South to look for open water. A lot of them will likely migrate north to Canada to breed. Mallards are also reliant on open water (as many waterfowl species are) so many are obligate migrants. I also spotted some Ring-billed Gulls whom are obligate migrators. The Brown-headed Cowbird is a facultative migrant as many can survive in North America, including Vermont, without necessarily having to migrate. Cowbirds are extreme generalists and are known to lay eggs in other birds' nests. They also roost with one another as mentioned in the previous paragraph.
Mini Activity: After analyzing the distances of the each of the migratory species, the cumulative distance from the Intervale to the wintering locations of the species I observed was ~2,500 miles. Many of the migratory birds that I spotted only migrated across North America, and not between continents.
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