Yellow-bellied flycatcher: The ‘moss tyrant’

By Joan Collins

The yellow-bellied flycatcher is a small (chickadee size), migratory, boreal bird that flies under the radar for most people. Little is known about this elusive species nicknamed the “moss tyrant” (“tyrant” taken from the flycatcher family name Tyrannidae and “moss” given its habitat preference).

Within its genus, Empidonax (from Greek “master of the gnats”), it is the most distinctive species member in appearance, with a yellow belly and a yellow-white, complete eye-ring. Other flycatchers in this genus have such similar appearances that it can be difficult for people to tell them apart by sight. Vocalizations are often the only way to easily differentiate the species.

The yellow-bellied flycatcher is late to arrive in spring and early to leave in mid-summer. It has one of the shortest stays on the breeding grounds of any Neotropical bird, often less than 70 days. It breeds across the boreal forest of Canada, the northern parts of Michigan, Wisconsin and Minnesota and the Northeast. Most of its year is spent on the wintering grounds in southeastern Mexico and Central America.

True to its nickname, this species breeds in habitats with thick mossy ground cover in moist coniferous or mixed forests, bogs and swamps, with shrubby undergrowth. It blends into the thick habitat with its overall yellowish-olive coloration making it difficult to spot. In the Adirondacks, yellow-bellied flycatchers are found in both low and high elevation boreal forest.

Nests are on or near the ground under tree roots, in a log, in sphagnum moss or at the base of a fern clump, and always well hidden by moss or overhanging vegetation.

Flying insects, hunted in the understory and captured in flight, make up most of its diet.

The yellow-bellied flycatcher’s short song is another reason it flies under the radar. It sounds like a fast “che-lik” (some find it similar to the least flycatcher’s louder “che-bek”). It throws its head back as it gives its quick song.

With all the other vocalizing birds, it can be a difficult sound to pick out, and people often can’t hear it until I focus my scope on one. Then they can watch the bird’s head snap up as it gives its song. Their call is a much more distinctive “per-wee” or “tu-wee” (somewhat like the Eastern wood-pewee’s longer “pee-wee” vocalization).

The males sing from exposed perches about 10 to 30 feet up. In low elevation boreal forest, they are difficult to spot singing in mid-story height. I find it easier to view them at high elevation singing from exposed snags, which are taller than the surrounding stunted balsam fir trees. I regularly see them on Whiteface Mountain’s summit area where Jeremy Kirchman, New York State Museum curator and ornithologist, has documented that yellow-bellied flycatchers have moved upwards over a thousand feet between 1973 and 2014 due to warming spring temperatures.

Globally, yellow-bellied flycatchers are increasing in number particularly in the northern part of their breeding range in Canada, and they have also expanded into eastern Alaska.

Breeding Bird Survey data indicate that the species is declining in the Northeast and adjacent Canada. Yellow-bellied flycatcher habitat is not easily accessible, so the Vermont Center for Ecostudies Mountain Birdwatch Project is invaluable with yearly monitoring of montane habitat in New York, Vermont, New Hampshire and Maine. Their data for 2010 to 2022 show strong evidence for a negative population trend overall in these four regions for yellow-bellied flycatcher.

The Catskills show strong evidence for a negative trend, where the species has gone from uncommon with 46 individuals detected on surveys in 2011, to almost absent with only six individual birds detected in 2022. The Adirondacks show weaker evidence for a negative trend. Climate modeling predicts the species will be gone from the lower 48 states by 2080, and from 73% of its current breeding range as the species moves northward.

I hope readers are fortunate and spot the moss tyrant in the summer of 2023.