Date: 5/29/18 12:06 pm From: Floyd, Chris <chrisf...> Subject: FW: [MASSBIRD] RE: Very Likely Bicknell's Thrush at Mt. Auburn, 5/28/18
Well, analyzing Gray-cheeked/Bicknell’s song structure has studied complexities I was not aware of. I forward with his okay analysis by Sean Williams that puts the songs I recorded into the Gray-cheeked category. I am still sorting out for myself the paper (deleted from this forward) that is the basis of Sean’s analysis.
From: Sean Williams [mailto:<seanbirder...>]
Sent: Tuesday, May 29, 2018 10:22 AM
To: Floyd, Chris <chrisf...>
Subject: Re: [MASSBIRD] RE: Very Likely Bicknell's Thrush at Mt. Auburn, 5/28/18
Wow, thank you for the extensive notes and documentation on this thrush. We hardly ever get recordings of full songs, which is the only reliable way to tell these apart in the field. Thanks!
You provided recordings for five songs (four in the first audio, one in the second), and of those, the second and fourth song in the first audio are the only full songs. By "full" song, I mean that they contain all four parts of a Bicknell's/Gray-cheeked Thrush song. These parts are labeled as parts I, II, III, and IV by Ouellet (1993), which I have attached here. According to Ouellet, the final phrase of the song, i.e. part IV is the most useful (perhaps the only definitive part) in distinguishing Bicknell's and Gray-cheeked. In Bicknell's, part IV should either rise or remain constant in frequency, and it should have a peak frequency of 6 kHz. In Gray-cheeked, part IV should fall in frequency and have a peak frequency of 5 kHz. In both of the full songs you recorded, part IV falls in frequency and has a peak frequency of 5 kHz.
This is all to say that the full songs you recorded match Gray-cheeked Thrush and rule out Bicknell's Thrush. The other songs in the recordings do not contain all four parts of the song, and so therefore cannot be used for identification. I have double-checked this with some of the other eBird reviewers for the state, and they agree.
I am happy and open to hearing your thoughts on this. This is a very tricky identification for which we have little to rely on with birds only observed in the field (and not in the hand). Thanks so much again for the awesome documentation.
On Tue, May 29, 2018 at 8:43 AM, Floyd, Chris <chrisf...><mailto:<chrisf...>> wrote:
I’ve updated my eBird report again with extensive notes for both photos and audios. I am now more confident that identification as Bicknell’s is correct, although I am eager for any feedback that would enlighten me on observations that I may be misinterpreting to this conclusion. I still have some wing formula lookup to do in Pyle but I am away from home.
By the way, I only hear the audio songs easily, even on my volume-maxed recordings, with my high-frequency-boosted hearing aids in.
I went to Mt Auburn yesterday, with very limited time, specifically to find a Gray-cheeked Thrush (and secondarily perhaps a Mourning Warbler), and I found this. The weather seemed ideal, since I’ve found them (GCTHs) so regularly over the years on rainy, drizzly days, singing atop small tombstones, which they seem to prefer.
It was the first bird I heard, singing, when I got my hearing aids in, after parking in my regular spot on Beech Ave near the Dell. I did a quick scan all around, and there the bird was, sitting a atop one of a pair of the smallest tombstones in view over toward Locust Ave, 25 paces away. I was first struck by the warm color (for a GCTH) with a closer view, but only gradually began to hear the BITH character of the soft singing as I followed the bird around. Some of the songs I heard seemed not to have the ending upturn. But the recordings seem convincing to me for BITH.
This was my second confident Bicknell’s for Massachusetts, the first being a bird I found in Mt Auburn on May 25, 2008, just southeast of the tower. That bird sang and sang on that sunny day from dense foliage in a small tree and was heard by many, seen by just a few (not by me), photographed by Paul Cozza, but unfortunately not audio-recorded.