- August 5-11, 2002:
- Out of 37 species banded this week, ten were new for this fall's banding list, which now totals 44 species. Among these was Yellow-throated Vireo, an infrequently caught species at Powdermill that is easily "missed" during the fall banding season. On average we band only 1-2 YTVIs in the fall, because it is both a rather uncommon and comparatively high-ranging species (i.e., typically foraging in higher layers of vegetation above the height of our nets). The YTVI banded this week certainly was not a fall migrant, but rather a disheveled and heavily molting adult.
- Another species that rarely makes it onto our fall banding list (in this case because most have departed their breeding grounds before the official beginning of the fall season in August) is the Louisiana Waterthrush. An adult banded this week in the very last stages of wing molt (probably an unusually late nesting bird) was caught in the same net round as an adult Northern Waterthrush (an early migrant of that species), also in the very late stages of wing molt.
Although we have posted comparison photos
of these two species before,
we couldn't pass up the chance for another (and we think better than previous)
side-by-side photo shoot of these two look-alike Seiurus species
(NOWA on the left; LOWA on the right). Differences between
the two species visible in the photo series below (several also noted previously)
include yellower, more heavily streaked underparts in the NOWA; whiter
(and wider) supercilium (eye stripe) and a whiter, more prominent subocular
crescent (lower half of an eye ring) in the LOWA; a much more noticeably
streaked chin in the NOWA; lastly, a much heavier (deeper at the base)
bill in the LOWA.
- There were thirteen species of wood warblers in all banded this week, and among them eight genera (and much of the ecological variation in the family) were represented. In addition to the well known plumage differences among the many wood warblers, the genera (and, in some cases, species within genera) tend to have characteristic bill morphology that is related to differences among taxa in foraging ecology.
In the photo plate below the underside
of the bills of nine species from eight genera banded this week are shown.
From left to right, top row: Ovenbird (genus
Seiurus),
Kentucky
Warbler (Oporornis),
Common
Yellowthroat (Geothlypis); middle row:
Blue-winged
Warbler (Vermivora), Black-and-white
Warbler (Mniotilta), Chestnut-sided
Warbler
(Dendroica); bottom row: Canada
Warbler (Wilsonia), Hooded
Warbler (Wilsonia), American
Redstart (Setophaga).
- In addition to differences in the shape of the bills (for example, note the proportionately very long and narrow bills of the BWWA and BAWW (middle row, left and center), species that feed primarily by probing into tight buds and bark crevices, respectively), note the difference in development of rictal bristles, the specialized hair-like feathers at the base of the bills that ordinarily are most well-developed in species (from many bird families) that engage in aerial foraging (i.e., flycatching) behavior. Although this correlation between bill morphology and behavior seems clear (and the function of the rictal bristles as a "net" of sorts seems intuitive), the functional morphology of these feathers in the context of aerial foraging actually has not been conclusively determined. Nonetheless, among the flycatching wood warblers, AMRE (bottom right) is the most convergent in bill morphology to the true flycatchers--in addition to its very well-developed rictal bristles (a trait that also is very well developed in the true flycatchers), the bill of the AMRE is more shortened, flattened and keel-shaped, giving it a proportionately very wide gape, a clear advantage when it comes to snatching flying insects out of the air!
- Finally, in our notes for the last week of July we posted a picture of the wing coverts and alula of an immature Black-and-white Warbler and said that we would post a comparative photo showing the corresponding feather pattern of an adult at the earliest opportunity--that opportunity presented itself today. To restate the point made previously, the juvenal BAWW middle alula feather (bottom frame) always has just one or two white corner spots that do not meet at the tip of the feather, whereas the adult middle alula (upper frame) has a variable, but always continuous white terminal band. This is very helpful, because distinguishing between juvenal and the equivalent or adjacent adult feathers often is a matter of judging more subtle differences in color, lustre, shape, and wear.
