ML620232397

Age

Not specified

Sex

Not specified

Behaviors

Foraging or eating

Observation details

What appears to have been the same bird (based on plumage details and site fidelity) was first reported May 16, and I came down early this morning to try to record it singing or calling while it was more likely to be vocal and before background noise got too bad. I took a skeptical approach coming in—there had been a lot of what appeared to me to be groupthink and confirmation bias happening over the last three days around this bird. I arrived in the Ramble shortly after 6 a.m. and encountered one other birder in the vicinity of this bird's favored site (the rocky area north of Azalea Pond). I soon heard the bird calling and then singing (often at a very low volume) and had several looks at it as it worked a circuit around the area. It spent a lot of time foraging on the forest floor for worms and other prey, sometimes whisper-singing as it foraged. Every few minutes, it would return to a higher perch to sing and call briefly, and then it would drop back down to resume its foraging loop. The bird's overall cool brown upperparts, plain and pale face, moderate blackish spotting on the upper breast, and vocalizations immediately placed it in the GCTH/BITH species pair and ruled out all other Catharus thrushes and WOTH. Some pale-tipped greater coverts indicated that bird is a first-spring (AHY) individual, as several observers had noted in preceding days. See photos attached. I believe the songs documented here provide good evidence that this was indeed a Bicknell's Thrush, though the recordings and spectrograms are rather noisy (due to Manhattan's constant din and because I need to get a better recording setup). In particular, many songs end with a very quick downslurred note followed immediately by another note that similarly slurs downward but then bends back upward in pitch and ends on a fairly level (or slightly rising) trill that is noticeably higher pitched than the low points of the preceding downslurred notes. This seems to be a fairly reliable feature of BITH songs, especially across multiple songs over a period of time (e.g., here and here). By contrast, Gray-cheeked songs tend to end on two or three notes that slide rapidly up and back down in pitch (almost flycatcher-like), and if the final note ends on a trill, the pitch of the trill tends to stay down near lowest frequencies in the whole song (e.g., here and here). Some Gray-cheekeds can apparently sing at least some songs similar to a typical BITH song (examples), but this does not seem to be the norm. As noted at the preceding link, BITH songs average slightly less rushed than GCTH, averaging about 2.5 seconds (vs. about 2 seconds, for GCTH) in length—and my recordings of this bird show that slightly longer per-song duration. My recordings also captured numerous calls, which are highly variable and overlap extensively across this species pair. Most of the calls captured here peak immediately in pitch and some hit 5,000 Hz and above, which is on the BITH end of the spectrum in variation (see Paul Driver's comment from January 2, 2014 near the end of this lengthy discussion). I see this as further loosely supportive, though not conclusive, evidence for this bird's identification, particularly given the relatively poor quality of my recordings.

Technical information

Model

NIKON D7100

Lens

70.0-300.0 mm f/4.5-6.3

ISO

3200

Focal length

300 mm

Flash

Flash did not fire

f-stop

f/6.3

Shutter speed

1/160 sec

Dimensions

2328 pixels x 1552 pixels

Original file size

1.85 MB