Pictorial_Highlights

POWDERMILL NATURE RESERVE
PICTORIAL HIGHLIGHTS
APRIL 15-21, 2002

Sunday, April 21, 2002:

The first two nets we checked this morning produced 35 American Goldfinches, which was quite a sight, because more than half of them were brightly plumaged males. With such a good head start, AMGOs (67 banded) topped the day's banding list, with 11 Ruby-crowned Kinglets being a distant second. Five new species were banded for the spring, including House Wren, Black-and-white Warbler, Ovenbird, Hermit Thrush, and Wood Thrush. In addition, recaptures of a returning White-eyed Vireo and Northern Parula banded last spring and summer were the first of these species in our nets this spring. Sorry, but the digital camera was not operational again today. Below is a picture of a NOPA (in a very similar plumage to the one recaptured today) that published on this website previously.

Friday, April 19, 2002:

Although they were first observed at Powdermill more than a week ago, we only banded our first Blue-gray Gnatcatchers today. Although male and female BGGNs cannot be distinguished in their Basic (i.e., nonbreeding) plumage, in the Alternate, or breeding, plumage the male (left photo) has distinctive black "eyebrows" that the female (right photo) lacks. These "eyebrows" are lost after the male undergoes its Prebasic Molt in the late summer.

Ordinarily, but not always, males and/or older birds return first to their breeding grounds. A significant tendency within a species for one age and/or sex class to arrive earlier or later relative to another is termed differential migration, and this phenomenon has been studied extensively by Powdermill's principal bander, Robert Leberman. Not unexpectedly, therefore, the first Yellow Warbler (top photo) banded at Powdermill this spring was an adult (i.e., after second year, ASY) male. Recall that yesterday's first Blue-winged Warbler, a returning banded bird, also was an adult male (see notes for 4/18 below). In Nashville Warblers, on average, males precede females by a week or more, however, the first NAWA banded this spring was an ASY female (bottom photo).

Thursday, April 18, 2002:

We opened our nets to the singing of a Wood Thrush (the first we've observed at Powdermill this spring), which gave us hope that there had been an influx of migrants overnight that would manifest itself as plenty of new (i.e., unbanded) birds, and at least a few new species, in our nets. As it turned out, birds were few and far between (only 26 banded) and most of the species could just as easily have been caught in February or March! The one bright spot was our recapture during the very first net round of an adult male Blue-winged Warbler (the first of its species recorded at Powdermill this spring). It was originally banded as a hatching year (HY) bird on 8/18/96, making it almost six years old. Before today, its only other recapture was on 5/21/98. The bird's comparatively broad, yellow-edged wing bars are suggestive of some intergradation with Golden-winged Warbler.

White-throated Sparrow--'nuff said!

Wednesday, April 17, 2002:
Yesterday we banded just 19 birds total--today we banded 19 Ruby-crowned Kinglets alone, and our total and capture rate were about three times that recorded yesterday. Among 14 species banded, just one, Hooded Warbler, was new for the spring. This bird provides our earliest ever banding record of the species by five days. A few other migrants were observed (but not banded) for the first time today, including White-eyed Vireo and Northern Parula. Because of low batteries, photos of the HOWA did not turn out well, but photoediting salvaged one image (don't mess with Arnold Schwarzewarbler!)

Another wood warbler banded today was our second Louisiana Waterthrush. We plugged the camera in for this one and got some better shots. We color-banded this bird as part of our ongoing studies, since 1996, of the population biology of the species at Powdermill. We purposely posed the bird with its one bright pink band next to a blooming redbud tree, just to spruce up the website a little! The bird was a second-year (SY) female. Molt limits on LOWAs can be very difficult to discern (and even more difficult to illustrate with a photo)--they usually occur between the small proximal feather of the alula (i.e., the alula covert), which ordinarily is included in the first prebasic molt of the species (and many other wood warblers, as well), and the two larger distal alula feathers, which are never molted by hatching year LOWAs. The three alular feathers are those paralleling the diagonal cut in the upper right corner of the bottom photo.

Tuesday, April 16, 2002:

Only 19 birds of 10 species (none new for the season) were banded today, despite our running 34 nets for almost five hours beginning at 6:15am. We banded our third Brown Thrasher of the season. It was aged SY (second year, or hatched in 2001) based on a molt limit (photo below) between four outer retained juvenal greater wing coverts (the feathers forming the right half of the lower wing bar). Compared to the inner greater coverts (three of which show well in the photo) that were replaced during its partial first prebasic (i.e., post-juvenile) molt last fall, the retained outer coverts are duller, lighter colored, and have less distinct subterminal black markings. Retention during the first prebasic molt of several outer greater coverts is typical for mimic thrushes (like thrashers and catbirds) and, also, true thrushes (e.g., robins, bluebirds, and spot-breasted species like Wood Thrush).

Molt limits are quite variable within and among species. Today (4/16) we banded an SY male Eastern Towhee whose molt limits indicated a much more extensive first prebasic molt than we have ever observed for the species, and, apparently, a more extensive molt than is known for the species, based on information in Pyle's (1997) Identification Guide to North American Birds. During the 1st PB molt, EATOs typically replace all juvenal wing coverts except the primary coverts; they frequently molt their tertials (the inner three secondary flight feathers, secs. 7-9) and less often their rectrices (tail feathers). The bird we banded today had molted all of these feathers and, in addition, its outer six primary flight feathers (prims. 4-9) and an additional two inner secondaries (secs. 5&6).

The atypical replacement of these flight feathers was made more obvious by the fact that the retained juvenal primaries and secondaries, which formed a block of seven feathers in the middle of the wing, had an even "fault" bar (i.e., a daily growth bar made particularly obvious due to a lapse in nutrition when the juvenal feathers were developing synchronously during the nestling or early fledgling stage). This fault bar ended abruptly where the replaced primaries and secondaries began. The photo below did not turn out as well as we hoped, but the molt limit between darker molted flight feathers and the browner retained juvenal feathers (those opposite the diagonal cut at the bottom right of the photo) nonetheless is evident. The fault bar, although not very obvious in the photo, can be seen about midway from the tips of the retained flight feathers.

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