FJ5

4/3/2021
Start Time: 9:20 am
End Time: 12:00 pm
Location: Missisquoi National Wildlife Refuge
Weather: 50º F, no wind/precipitation
Habitats: marsh surrounded by young deciduous forest, large open field across road

Migration is a time-consuming and energetically-costly endeavor. It is therefore understandable that many species stay in an area year-round, especially if their diet and lifestyle allow them to do so. In order for the benefits of migration to outweigh the costs, reproduction must make up for the high mortality rate experienced during migration. Mortality resulting from staying in the breeding area year-round must also be sufficiently high so that overall survival is drastically improved with migration. Many of Vermont’s non-migratory species, such as Black-capped Chickadees, Tufted Titmice, and American Crows, are generalists that can cope with the decrease in available food by being able to survive on a range of different food sources depending on availability and time of year. During their pre-basic molt, many species will also grow in additional down feathers for extra insulation during the colder winter months.
American Robins are an example of a facultative migrant than can adjust their migration in response to environmental conditions. Depending on current conditions, individuals may or may not leave Vermont for the winter. It’s possible that many of the robins encountered are returning to Vermont after wintering farther south, or travelled south from farther north to winter and are on their way back north.
A few obligate migrants are beginning to return to Vermont already. Returning relatively early, before most other migrants, may grant these species exclusive access to resources before other migrants begin to arrive. Arriving in early April also likely allows more time for breeding and rearing young, and may potentially grant some of these species the ability to raise an additional brood. However, one disadvantage to arrive this early is that weather is still somewhat unpredictable, and likely less mild than it would be had they arrived sometime in May.
For this mini activity, I calculated the distances travelled for American Kestrel, Northern Harrier, Wood Duck, Osprey, and Tree Swallow. I estimated each species’ wintering area to be around the Everglades in South Florida, near the Neuse River in North Carolina, near Willington, Georgia, near the Florida Keys, and near Jacksonville, Florida, respectively. The total distanced travelled by all five species was calculated to be around 5,566 miles.

Publicado el abril 4, 2021 06:51 TARDE por gracey4