Pictorial Highlights, 2nd half April 2003

POWDERMILL NATURE RESERVE
PICTORIAL HIGHLIGHTS
Second Half of April 2003

Saturday, April 26, 2003: The predicted overnight and early morning rain showers didn't materialize beyond a very light drizzle, and conditions were otherwise mild, overcast and calm--in other words, ideal for banding! This was a good thing for Dr. Gary Williams and his Ornithology class who drove up last evening from Frostburg State University in order to see the banding early this morning. Brian Jones, who also happens to be a student in the same Ornithology class that visited the banding lab this morning, helped with the banding today.

Despite excellent weather conditions for catching birds, there apparently were relatively few birds in the banding area today, and our overall capture rate (<10 birds/100 net hrs.) was quite low. Notwithstanding this, two new species to band (Ruby-throated Hummingbird and Least Flycatcher), as well as a few others observed in the field (House Wren, Yellow-throated Warbler, and Yellow-throated Vireo), provided evidence that there was some turnover of birds in the banding area overnight.

As part of our ongoing studies of the population and breeding biology of the species, we color-banded two second year (SY) probable female Louisiana Waterthrushes caught during routine mist-netting in the banding area. Their age was based, as usual, on wing molt limits (see first photo below), with the molt limit in both birds between molted greater coverts, carpal covert, and alula covert and retained juvenal secondaries, primary coverts, and middle and lower alula feathers (note: the apparent differences in wear between the very worn median and lesser coverts and the fresher looking greater coverts is not a molt limit--all these feathers are from the first basic plumage, they have simply become worn to different degrees because of their different positions on the wing). Another word of caution: some adult LOWAs apparently winter in areas where their plumage becomes exceedingly worn, and differential patterns of wear in such individuals can sometimes mimic true molt limits; similarly, some SY LOWAs that winter in areas where plumage wear is minimal can appear very fresh in spring, with their molt limits being much less obvious than those in the bird pictured below (always look for corroborating characters like the shape of the tail feathers or fault bars).

Both LOWAs (one pictured in second photo below) were provisionally sexed based on two criteria: first, their comparatively short wing chords, 77.0mm and 79.5mm (based on a sample of >100 known sex SY LOWAs, we have calculated that birds with wing lengths <78.5mm can be sexed female with >95% confidence, and for known adult, ASY, LOWAs, the cutoff, also calculated based on ca. 100 known sex birds, was calculated to be 79.0mm. This analysis, part of a larger study of body mass and wing length variation for 170 species based on 300,000 Powdermill banding records may be published shortly as a monograph of the Eastern Bird Banding Association); second, sexing as female was supported by the lack in either bird of any cloacal protuberance like males ordinarily display at this time of year. In fact, even outside of the breeding season, there can subtle differences between the sexes in the configuration of the cloaca, as discussed and illustrated in Lars Svensson's seminal guides to the identification of European passerines, and both these two birds showed the broad, flat cloacal region typical of females.

White-throated Sparrow topped our banding list today--with 11 banded yesterday and another 16 today, this is shaping up to be our best spring WTSP flight in recent years (we have to go back to 1996 to find daily spring banding totals >10 for this species at Powdermill).

During the recent EBBA meeting here at Powdermill, it was stressed during various presentations and workshops on the subject of using wing molt limits to age birds, that a bander's own careful observatiolns ultimately will be their best "guide" to the subject. Therefore, without taking undue lengths of time, banders should always take the fullest possible advantage of the time during processing of birds to quickly scrutinize each bird's plumage, especially the wings and tail. You just never know what interesting variations you may see. For example, today we handled an SY Swamp Sparrow that had an extra feather in its alula (on both wings), inserted between the middle alula and the so-called alula covert (giving it a total of four rather than the usual three feathers in this group).

Although the above bird was something of a curiosity, banders shouldn't miss opportunities to take notice of unusual aspects of a bird's plumage that may be very instructive for making age determinations of other individuals of the same species. Case in point, today and yesterday at Powdermill we banded second year (SY) individuals of three different sparrow species that exhibited asymmetrical replacement of tertials (i.e., inner three secondaries nos. 7, 8, & 9), either adventitiously, (i.e., following accidental loss) or during the normal first prebasic molt.

In each case, the asymmetrical molt served to highlight the difference between real molt limits (i.e., differences in appearance between feathers or feather groups resulting from their having been grown during temporally separate molts) and pseudo-molt limits, which can result from differences in color and pattern between feathers or feather groups that can make them appear as though they represent different feather generations when, in fact, they were grown during the same molt. Because there can be considerable difficulty in recognizing and interpeting molt limits for species like the Chipping Sparrow, Swamp Sparrow, and White-throated Sparrow, which can show strong pseudo-limits among feathers of the same generation (e.g., tertials and greater coverts), finding and studying birds like those pictured below can be very instructive and help to guide a bander's eye toward more readily distinguishing between real and pseudo-molt limits in other individuals of the same species.

In this CHSP, the tertials on the left side of the photo are all retained juvenal (the difference in appearance between the smallest tertial, secondary 9, and the other two being a pseudo-molt limit), while sec. 8 & 9 on the right side of the photo were replaced during the first prebasic molt

In this WTSP, sec. 8 among the tertials on the left side of the photo molted last fall; sec. 9 on the right side also molted. The asymmetrical molt makes it possible to directly compare the juvenal middle and inner tertials (which can give a pseudo-molt limit among the tertials or between the tertials and the other secondaries) with their non-juvenal counterparts.

In this SWSP the situation is more complicated (and, unfortunately, the picture is less good): the middle tertial (sec. 8) on the left side of the photo was replaced during the first prebasic molt (compare to the more worn counterpart on the right side of the photo), while the almost equally dark-looking (but visibly more worn) inner terial (sec. 9) is a retained juvenal feather (compare it to the molted sec. 9 among the tertials on the right side of the photo). Although only the inner tertial (sec. 9) molted on the right side of the photo, the almost equally dark-looking sec. 8, a retained juvenal feather, gives a pseudo-limit with sec. 7, a contrast not very dissimilar to the true molt limit between molted sec. 8 and retained juv. sec. 7 on the opposite side. Only by being able to directly compare the appearance of the molted and unmolted secs. 8 & 9 between wings, does it become possible to confidently sort out the real and pseudo-molt limits in this bird.

Tuesday through Friday, April 22-25, 2003: We banded 146 birds of 31 species. Six new species for the spring included Tree Swallow, Wood Thrush, and four wood warblers. One of the warblers, an after second year (ASY) male Northern Parula banded on 4/24, is the "cover bird" for our new home page, but you can be sure that we took more than one photo of a bird that looked that good, so here's another!

Our first Prairie Warbler of the season on 4/22, also an ASY male, was no slouch either!

The Worm-eating Warbler banded on 4/22, an SY bird, was a little less photogenic!

Wednesday through Sunday, April 16-20, 2003: Among the expected migrants this week were Ruby-crowned Kinglets. The first of this species was banded here on 4/8 with no others until this week, when 23 RCKIs were banded, topping the week's banding list. Next most commonly banded birds this week were Swamp Sparrow (19), American Goldfinch (17), Dark-eyed Junco (15), and Chipping Sparrow (12).

Among the unexpected species or unexpectedly early migrants this week (pictured in order below) were two individuals of the earlier migrating "Yellow" eastern race of the Palm Warbler and a Grasshopper Sparrow on 4/16 (only our 15th spring-caught GRSP in 42 years, and the earliest by a week), an early Blue-winged Warbler on 4/17 (our previous early banding date was on 4/21/85), and an exceptionally early Red-eyed Vireo on the same date (only two REVIs have been banded here in April, both more than ten days later than this week's bird).

Grasshopper Sparrow

Blue-winged warbler (SY male)

Red-eyed Vireo

Other interesting birds from this week (again pictured in order below) included our first Blue-gray Gnatcatchers of the season, a pair of Belted Kingfishers captured together in the same net (photo shows a comparison of their breast bands--male left, female right; this is one of very few bird species in which females are both slightly larger and more brightly colored than males), a Hermit Thrush (a very clean-looking ASY bird), and a Brown Creeper (make that a Frown Creeper!)

Belted Kingfisher breast bands (male left; female right)

Hermit Thrush (ASY unknown sex)

Brown (Frown) Creeper

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