Four high-pitched whistles in a monotone, and then there perched before me the rarest of the rare-a little Beardless Flycatcher. This toy tropical creature appeared right at home in the heat-prostrated stream bottom. Nature always contrives to do something surprising for the birdman! It seemed like a farewell challenge to return for another season .
Herbert Brandt (in Arizona) 1951
This tiny gray flycatcher that resides across much of Mexico and Central America reaches the United States only in extreme southern Arizona, New Mexico, and Texas, and only in small numbers. Here it resides inconspicuously in riparian woodlands, where it is easily mistaken for verdin, vireo, warbler, or Empidonax flycatcher. Identification is perhaps best made by voice, based on its distinctive, high-pitched pee-pee-pee or pier notes.
The Northern Beardless-Tyrannulet is the only U.S. representative of the Elaeniinae, a large subfamily of mostly South American tropical tyrannid flycatchers. In Costa Rica, its range overlaps slightly with a sister species, the Southern Beardless-Tyrannulet (Camptostoma obsoletum). Like other primitive elaeniine flycatchers, its bill shape and foraging behavior are more suggestive of vireo or warbler than of flycatcher. This tyrannulet seldom fly-catches like a pewee or phoebe, but instead uses its compressed, arched, vireo-like bill to pick and glean insects from bark and foliage. "Beardless" refers to the absence of rictal bristles, which are present on most flycatchers, at the base of the bill. "Tyrannulet," a diminutive of "tyrant," alludes to its aggressive chasing of potential small predators that might prey on its eggs or young. In many ways the Northern Beardless-Tyrannulet is a typical tyrannid: sexually monomorphic, a monogamous breeder, and vigilant in the care of its young.
The drab, diminutive female tyrannulet constructs an elaborate, domed, globular nest with a side entrance. Nests are sometimes concealed inside webs of tent caterpillars or spiders, between clumps of ball moss or achiote seedpods, and in clusters of juniper needles.
The elusive habits of the Northern Beardless-Tyrannulet may partially explain the lack of research and natural history information on the species. A study in Texas by Brush (Brush 1999b) has contributed to our understanding of its behavior and breed-ing biology. Such information is vital, since lowland riparian woodlands favored by the tyran-nulet continue to disappear as a result of deforestation.