The presence of Blackpoll Warbler, Gray Catbird, Swainson's Thrush, and Gray-cheeked Thrush has been constant. Their numbers will continue into early October.
|Brewster's Warbler (BRWA)|
A pleasant surprise for the season
One such species beginning to arrive that can be easily aged and sexed (often through binoculars) is the Rose-breasted Grosbeak. They often reveal their presence with their distinctive and loud "chink" call. In fall migration the males, both Hatching Year (HY) and After Hatching Year (AHY) are donning their basic plumage where the body feathers match closely to those of the female grosbeak.
|HY Male Rose-breasted Grosbeak (RBGR)|
Note the begining of a pre-supplemental molt
in the greater and median coverts of this individual.
|Note the pink or "rose" under the wings and a tiny spot of rose on the breast.|
|Dorsal View of the HY Male RBGR|
The basic plumage looks similar to female. The few black feathers seen are a result of a pre-supplemental molt. It will molt into its alternate plumage on the wintering grounds.
As a group, the Bay-breasted and Blackpoll warblers have to be two of the most confusing fall warblers. There are distinctive leg coloration differences with the BLPW having lighter colored legs and yellow pads to its feet and the BBWA having darker legs with gray pads to its feet. These are helpful even in the field as the lighter leg color of the BLPW will reflect light differently than the dark gray leg of the BBWA. Additional field marks that help both in the field and the hand are the many streaks found on the flanks of BLPWs and the somewhat clear flanks of the BBWA. Both species show considerable streaking in their backs that separates them from the similar Pine Warbler that has a clear back.
Even in the hand, banders must work hard to determine the age and sex of BLPWs. Knowing the sex and age demographics of a population gives information supporting the condition of the population. For example, having no juveniles or HY during fall migration is a signal that there may have been poor production on the breeding grounds. Understanding the age and sex structure of the banded sample can give clues to where in migration a location is at in migrational timing for the given season, age ratios for life cycle modeling, and even some indication of how important a site may be to the species as adults tend to show more site fidelity.
Here are examples of After Hatch Year (AHY) male BLPW and BBWA.
|Blackpoll Warbler (BLPW) AHY male|
Note: the light colored legs and streaking on the flank (just below the wing).
|Dorsal view of the AHY male BLPW|
Note: the many black streaks on the back. This often adds to the picture in determining the sex of a BLPW in the hand.
|AHY Male Blackpoll Warbler|
The dark bill is another useful tool in determining the age of this AHY bird.
|AHY Male Bay-breasted Warbler |
Note the rounded alula edged in white and the "bay' wash on the flanks.
|Dorsal view of the AHY male Bay-breasted Warbler|
Note the "bay" feather on its head.
BSBO will host a free Public Banding Demonstration this Saturday, September 26th at 10:00 AM at the Observatory.