Pictorial Highlights, Early Fall, 2010
August - September 2010
The official beginning of fall migration at Powdermill begins on August 1. Although the majority of migrants won’t move through the area until September and October, several species are migrating in August. Species included in this group are the empidonax flycatchers, which consistently present challenges to banders making species identifications. In eastern North America, most empid flycatchers can be readily identified by taking into account a few characteristics. First, look at the overall plumage of the bird. The Yellow-bellied Flycatcher is generally identified by their extensive yellow color throughout the underside and up through the throat (but be careful with hatch-year Acadian Flycatchers), medium gray legs, and medium sized wings. The Acadian Flycatcher has a yellow/green back, large bill, light gray legs, and long wings, lack emargination on primary 6, and HY birds often have buffy markings on their shoulder patch. The Least Flycatcher is the smallest of the empids and is characterized by a short wing, bold white eye ring, dark grey legs, and an emarginated primary 6. The Traill’s Flycatcher (Willow and Alder) has dark gray legs, a grayish back, thin eye-ring, lack of emargination on primary 6, and a long wing.
|From left to right: Least, Yellow-bellied, and Acadian Flycatcher.|
|A closer view: Yellow-bellied (left) and Acadian Flycatcher (right).|
One of the Least Flycatchers was captured with an insect in its lower mandible. Although the insect was still alive it stayed lodged in the bird’s bill throughout the hour between capture and being released after the banding process.
The term molt-migration is given to individuals that leave their breeding grounds and head south only to find a suitable location to undergo its pre-basic molt before it continues migrating south. This phenomenon is well documented in the arid landscapes of western North America, but is not documented for the majority of eastern North American species. A few exceptions are the Tennessee Warbler and Swainson’s Thrush. Even in these cases, molt-migrants account for a very small proportion of the breeding population.
Pictured is a Swainson’s Thrush in molt captured at Powdermill during August.
Although we failed to capture any Golden-winged Warblers this fall, we
did band two Blue-winged x Golden-winged Warbler hybrids.
Another hybrid bird. This one reminiscent of a Lawrence's Warbler
and is an after-second-year bird.
A Tennessee Warbler with an
overgrown upper mandible.
|A HY Gray Catbird with a crossed bill
|Two handsome adult male warblers.|
|An adult male Bay-breasted Warbler|
|The American Redstart is a species that has delayed plumage maturation. This HY male will resemble a female until it undergoes its second prebasic molt at the end of next summer. A young male often has brightly colored side patches, dark gray uppertail coverts, and more yellow on the 3rd retrix than young females.|
||The majority of Hooded Warblers
captured at Powdermill are breeders in the region rather than
actively migrating individuals. As with
many species of warblers, plumage is extremely helpful in
identifying the age and sex of the bird. HY females generally lack
any black hood, adult females have a variable amount of black in the
hood (from very little to nearly complete), HY males have a full
black hood with yellow tipping on the throat feathers, and AHY males
have a full hood with no to very little yellow in the throat.
Pictured is a hatching-year male Hooded Warbler.
AHY male Hooded Warbler
|A size comparison of a Bay-breasted Warbler (left) and a Magnolia Warbler (right).|
||Unlike many banding stations, we band all
of the Ruby-throated Hummingbirds that are captured in the mist
nets. This year, we banded 368 hummingbirds, with 271 of them
captured during August-September. The great majority of hummingbirds
can be aged and sexed based on their plumage with adult males having
full gorgets, young males having dark streaking in their throat, and
females having light throat streaking. They can also be aged by bill
striations and often sexed by wing chord as females average larger
Hatching year male
Male and female Black-throated Blue Warblers. At one time they were thought to be 2 separate species within the same genus. At one time, Audubon and Wilson both referred to the male as the Black-throated Blue Warbler and the female as the Pine Swamp Warbler (named after the Pine Swamp of eastern Pennsylvania).
A hatching-year Sharp-shinned Hawk. The prominent eye ridge above the eye was very noticeable in this individual and is thought to protect the eye while shielding it from excessive glare.