Tree swallows foraging over water with a double-crested cormorant onlooker (Shelburne Bay)

Spring migration is here

While the goal with Bird Club is to see and/or hear 52 different species over the course of 52 weeks, I’ve added a personal challenge to get quality photos of 52 species. I’ll be adding these photos to the bottom of the Bird Club web page as I capture them (scroll over the images for the names of species). 

Ruby-throated hummingbirds, gray catbirds, and an eastern bluebird were all friends I saw over the weekend, friends I haven’t seen since that late summer/early fall. With new species arriving daily, this time of year is always exciting (and a bit overwhelming). As birds return in droves, one question that pops up for me is what factors play into when each species (or even each individual) arrives back in Vermont.

Bird Club
A common grackle in beautiful breeding colors (North Beach, Burlington)

Obviously, distance plays a role. Some birds, like great blue herons, just pop over to the coast for warmer temperatures and better habitat, while barn swallows overwinter in South America. The farther a species travels for migration (particularly when there’s little to no overlap between winter and breeding grounds), the more dependent they are on changes in daylength. Others are more attuned to local changes in abundance of food and follow favorable changes in habitat to draw them northward. Ultimately, the underlying reason for the arrival of spring migrants swirls around some combination of food and sex.

Yellow-shafted flicker on a red maple (Centennial Woods, Burlington)

For flickers, their overwinter and breeding grounds are mostly the same (flickers in the northern parts of their range shift south), and migration seems largely driven by availability of food in their breeding grounds. Last week I was out in Centennial Woods when I heard the loud “Yak Yak Yak…Yak Yak” call of a male northern flicker (males have a black whisker under eye – see image above). I followed a group of two males and one female for about 20 minutes and watched their various courtship behaviors: acrobatic chases up, down, and around trees, aggressive displays, drumming against standing dead trees, and the Yak Yak Yak calling. The group slowly made their way out of the woods and back towards my house.

A male northern flicker foraging for ants (Centennial Woods, Burlington)

Two of the flickers landed on a grassy patch and spent the next 15 minutes foraging on the ground for ants. Ants make up about 99% of a flickers diet (source), so it’s no surprise that flickers arrive just in time to greet the ants as they emerge from their nests. The warm weather had brought out the ants (likely turfgrass ants, Lasius neoniger) and the ground looked like it had just erupted in hundreds of tiny little “sand volcanoes.” Like many other ants, turfgrass ants seal up the entrance to their nests in the fall and huddle around the queen to protect her from cold temperatures during the winter. In the spring, as the ground thaws and the sun warms up the upper layers of soil, the turfgrass ants clear out their nests, littering lawns and waste areas with small piles of sand at the entrance (pavement ants, Tetramorium immigrans, do the same).

A turfgrass ant poking its head out of the entrance to the colony (Backyard, Burlington)

The graph below shows the frequency in which northern flickers appear in people’s checklists submitted to eBird.org. Flicker’s are occasionally spotted in Vermont throughout the winter (about 2% of checklists submitted between December and March include flickers). but they don’t really start to be seen with any frequency until the ground begins to thaw in early- to mid-April. And while there aren’t many reports of turfgrass ants on iNaturalist, the majority are in April and May.

Frequency of observations of northern flickers for Chittenden County (from eBird.org)

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