ML236201491
Contribuidor
Fecha
Localidad
- Edad
- No especificado
- Sexo
- No especificado
- Playback
- No especificado
Detalles de la observación
Presumably the same Gray-cheeked/Bicknell’s Thrush (Catharus minimus/bicknelli) I observed, photographed, and videorecorded the previous morning (2020-05-17). Details of that observation are recorded in the following checklist: https://ebird.org/atlasny/checklist/S69224991 I returned to the same area on 2020-05-18 at 0534. On a whim, and without having any indication the thrush was still present, I played a recording of Bicknell's Thrush (song) once only. Immediately, what I presume was the same individual from yesterday shot out from some nearby roadside vegetation and perched on a branch. I got a few brief looks at it but nothing like the cooperative (however dimly lit) views from yesterday. However, after losing track of the bird visually for several minutes, the thrush began singing from the gully at 0544, first from further away (presumably, or it was singing more faintly at first), before moving uphill to the edge of the road. I began recording a video on my camera immediately, resulting in a 2:24 recording (abridged to 1:36 in the first audio file submitted here, but they’re from the same original recording; all time marks referred to below are from ML236552941). As I was recording, the thrush approached closely enough that I could see it without binoculars. I recorded it singing 21 songs (and it sang at least once before I was able to hit the record button, so I heard at least 22) before it flew off, calling five times as it flew away from me (also recorded, though these vocalizations from this species complex seem less reliably diagnostic). Of the songs I recorded, the first several are too faint or ambiguous to assess but the songs become easier to hear with the song beginning at 0:55. From 1:19 to 2:05, the thrush is singing more regularly and clearly, varying its song slightly each time but consistently upslurring the ending “trill”. As opposed to the “typically lower” ending exhibited in Gray-cheeked Thrush songs (cited by Nathan Pieplow in the Peterson Field Guide to Bird Sounds of Eastern North America, p. 336), this individual consistently reached frequencies in excess of 6 and 7 kHz on its final “note” (with some harmonics going over 8 kHz, as seen in one submitted spectrogram). Pieplow states that “[s]ome Gray-cheeked have final phrase identical to Bicknell’s […], but only in 1-2 songs of the repertoire” (p. 336); from 1:29 to 2:05, the individual I recorded sings nine consecutive songs, all ending with a distinctive rising pitch. It’s consistently noted in the available literature that relying on plumage (and behavior) cues in separating individuals in the Gray-cheeked/Bicknell’s Thrush complex is usually impractical on account of the difficulties of assessing these characteristics in field observations and because of considerable overlap in characteristics between the species (Sibley and others stress that they’re “best distinguished by song”). However, Bicknell’s Thrush is often described as averaging “more reddish”, particularly on the tail, with a shorter primary projection (also on average). The only photograph attached to this checklist (taken 2020-05-17 but presumably the same individual) shows a thrush that has a tail with a warmer, reddish wash (as compared to the rest of its upperparts) and the primary projection does seem shorter, though I don’t pretend to have experience assessing this feature in Catharus thrushes. Additionally, other photos attached to the 2020-05-17 checklist also show a thrush with a reddish cast to its plumage. Even without assuming I observed the same individual at the same location on two consecutive days (and it is probably prudent to rely on the recorded acoustical evidence anyway), I feel as confident as I can be given my limited experience with this species complex that I assembled sufficient evidence to identify the 2020-05-18 bird as a Bicknell’s Thrush — though I welcome informed opinions.
Información técnica
- Grabadora
- Micrófono
- Accesorios
- Original file size
- 16.17 MB