April 1, 2018

I spent three hours driving around south of Burlington around Shelburne Pond, Little Otter Creek, and the town of Charlotte. Most of my time was spent in the car, pulling off the road when I spotted a bird. Little Otter Creek was perfect for this as it was just long empty farm roads with massive fields on either side, Osprey and Bald Eagle nests, and the creek running close by. It was a beautiful sunny day, approximately 40 degrees Fahrenheit.

Most of the resident species I saw have the tendency to roost in larger groups to conserve heat. This includes species like the Eastern Bluebird, Black-capped Chickadee, Song Sparrow, Mallards, and American Robin. I also noticed a tendency for these non-migrants to change their food source as the winter approaches. Black-capped Chickadees, American Robins, and Eastern Bluebirds all shift their diets from mostly energy rich invertebrates in the summer and spring to mostly a seed and fruit diet in the winter. Changing their foraging habits as the food sources change through the seasons. Other species like the American Crow, Mallard, Herring Gull, Ring-billed gull, and Song Sparrow all have very broad diets from insects, to seeds/fruits, and vegetation that allow them to forage year round. Not necessarily changing their foraging habits specifically in relation to season.

The Red-tailed Hawk for example eats mostly mammals (hares, rodents, and small birds) that are available year round. However, the Osprey and Bald Eagle mostly rely on fish and so when the rivers and Lake Champlain freeze over they lose their hunting ground. This is why the Bald Eagle and Osprey are short distance migrants that return fairly early compared to other species. The Bald Eagle and Osprey are the perfect example of a facultative migrant. They return not based on a "hardwired" time for migration, but environmental cues like that of open water that opens up more food sources. These two species most likely are arriving now or in the past couple months from an area with open water, rather it be the ocean to the East or a warmer area in more southern states. This area is their nesting habitat for I saw one massive Bald Eagle nest that has likely been utilized and grown over the past several seasons. The Osprey may also return to the same nest year after year, depending on the success rate of hatchlings.

The Osprey is most likely the species with the longest migration I saw that day. A study completed on banded Ospreys showed that east coast nesters most likely come from South America or the Caribbean, with few coming from the southern United States but not in the best health (Henny and Van Velzen 1972, Poole and Agler 1987). It is possible that some of these individuals migrated over 3,000 miles to get here to Vermont. The two Ospreys I saw also are relatively early migrants, more to be expected in the next coming weeks.

Posted on April 5, 2018 05:16 PM by srotella