Friday, May 26, 2006

Gray-cheeked thrushes in Prospect Park

On Thursday morning Doug Gochfeld and I birded in the Midwood forest of Prospect Park. Over the last week or so we've seen a notable increase in migrating thrushes. Gray-cheeked-type thrushes have been fairly common. I figured that there was the possibility of a Bicknell's Thrush within the mix. Along with my bins and field guide I brought a small pair of portable speakers and a sound sample of the bicknell's song and call on my Palm Tungsten E.

We set-up near the bridle path at the north end of the Midwood where we noticed two gray-cheeked type thrushes feeding at the edge of the path. I placed the speakers on the ground, put the recording on endless loop and backed up about 20 feet. One of the thrushes responded almost immediately by hopping down the path and right up to the speakers. Compared to the thrush that didn't respond this individual had more reddish-brown wings, tail and rump. It didn't sing or call at that time.

Angry chipmunk

(Photo credit - Sean Sime)

I returned at the end of the day with Doug and Sean Sime. Sean brought along his camera gear. It didn't take us very long to locate a gray-cheeked with similar plumage. When I played the recording near the stairs at the end of the Midwood he hopped over towards the speakers until he was chased away by a chipmunk (yes, a chipmunk). We moved a short distance from this location and played the recording again. With no chipmunk nearby he hopped right towards the speakers. This time I heard him make a muted "veeerr" call. Sean, who was taking photos much closer to the bird also reported hearing it make, what sounded like, the rising, final segment of the bicknell's song.

Bicknell's Thrush (Catharus bicknelli), click for larger image




(Photo credit - Sean Sime)

After posting my questions and Sean's photographs online I received the following, enlightening response:

"I was most intrigued by your whole story. As far as I am concerned, the fact that it responded to a Bicknell's recording says nearly all (it would have been nice of it had also FAILED to respond to a Gray-cheek...).

I was curious to see the pix, and especially pleased when I did. The rufous tones to the wing and tail are there; the wing actually looks blunter than a Gray-cheek's (helps if you have handled some in banding); and most critical is that lower mandible: it is 3/4 fairly bright yellow with only a small dusky tip. Gray-cheek's is no more than 1/2 light, the rest being pale, even pinkish, yellow (if yellow at all).

In sum, to sort of back into the ID a bit, there is nothing WRONG for Bicknell's, and nothing RIGHT for Gray-cheek.

Both species must move through in good numbers; it's not as if Bicknell's is some Siberian vagrant. Banding studies in Queens in the 1930s revealed that the Gray-cheek:Bicknell's ratio was ca. 3:1 in spring, and 1.3:1 in fall, in a total sample of 378 birds. I see no reason why this RATIO should have changed, notwithstanding some overall reductions in absolute numbers of all 3 'northern' Catharus thrushes.

Nice bird!"


Below are some links with more information on Bicknell's Thrushes:

-A Species is Born-
-Species of special concern in Canada-
-Audubon Watch List-

1 comment:

John said...

Thanks for this explanation. The Gray-cheeked / Bicknell's split is one where I am on uncertain territory.

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