{"id":2480,"date":"2010-10-31T14:31:01","date_gmt":"2010-10-31T20:31:01","guid":{"rendered":"http:\/\/earbirding.com\/blog\/?p=2480"},"modified":"2016-11-25T08:22:41","modified_gmt":"2016-11-25T14:22:41","slug":"curve-billed-thrasher-identification","status":"publish","type":"post","link":"https:\/\/earbirding.com\/blog\/archives\/2480","title":{"rendered":"Curve-billed Thrasher Identification"},"content":{"rendered":"

The AOU checklist committee recently rejected a proposal<\/a> to split the Curve-billed Thrasher into two species: the “Palmer’s” Thrasher (palmeri<\/em> group) in Arizona and West Mexico, and the nominate or “Eastern” Curve-billed Thrasher (curvirostre <\/em>group) in the rest of the bird’s range.<\/p>\n\n\n\n\t\n\t\t\n\t\t
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\"Palmer's\" (Western) Curve-billed Thrasher, Desert Botanical Garden, Scottsdale, AZ. Photo by Patrick Coin (Creative Commons 2.0).<\/td>Nominate (Eastern) Curve-billed Thrasher, Colorado, by Fort Photo (Creative Commons 2.0).<\/td>\n\t<\/tr>\n<\/tbody>\n<\/table>\n\n

Although very similar, the two groups can usually be distinguished by sight. In the photos above, note that the eastern bird (right) has a much whiter background color to the breast, resulting in stronger contrast with the breast spots; it also shows sharper and bolder white highlights in the wings and tail.\u00a0 The stronger throat pattern, with a more distinct dark line bordering the white throat, may also be significant.\u00a0 However, the much colder, grayer tone to the plumage overall is likely an artifact of photo lighting.<\/p>\n

Interestingly, one of the committee members who voted “yes” on the split did so in large part because of differences in the call notes between the two forms, which I hadn’t seen discussed anywhere before:<\/p>\n

YES<\/strong>. I now favor splitting palmeri <\/em>– the clincher for me is that palmeri <\/em>has distinct call note differences, a clear upslurred whit-wheet, as opposed to a two note whit-whit in which both notes are the same.<\/p><\/blockquote>\n

I have investigated this difference, and it seems to hold up across (at least) most of the species’ US range.\u00a0 The vast majority of the call recordings I could find from well inside the range of “Palmer’s” Thrasher showed the same typical pattern: two upslurred whistles that started at the same pitch, with the second one ending much higher:<\/p>\n

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"Palmer's" Curve-billed Thrasher call, Catalina State Park, Pima County, AZ, 2\/23\/2008.<\/figcaption><\/figure>\nhttp:\/\/earbirding.com\/blog\/wp-content\/uploads\/2010\/10\/CBTHcWest-NDP2008-08-19.mp3<\/a><\/audio>\n

Whereas the call of eastern curvirostre<\/em>-group Curve-billed Thrashers consist of nearly identical notes, both upslurred across a wide frequency range like the second note of the “Palmer’s” call:<\/p>\n

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Nominate eastern Curve-billed Thrasher call, Carlsbad Caverns National Park, Eddy County, NM, 3\/30\/2008.<\/figcaption><\/figure>\nhttp:\/\/earbirding.com\/blog\/wp-content\/uploads\/2010\/10\/CBTHcEast-NDP2008-16-62.mp3<\/a><\/audio>\n

Both groups of Curve-billed Thrashers give versions of this call with 3 or more notes, particularly when they are excited.\u00a0 When the eastern curvirostre <\/em>group does so, as you can see in the spectrogram above, all the notes tend to be similar.\u00a0 When western palmeri<\/em> birds extend their calls, the first note is usually of the stunted variety.\u00a0 The third note (and any subsequent notes) tend to be like the second, but a little softer, so that the second note ends up getting the emphasis: “wit-WEET-weet”:<\/p>\n

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"Palmer's" Curve-billed Thrasher calls (3-noted version), Alamos, Sonora, 7\/3\/2010.<\/figcaption><\/figure>\nhttp:\/\/earbirding.com\/blog\/wp-content\/uploads\/2010\/10\/CBTHcWest3-NDP2010-05-512.mp3<\/a><\/audio>\n

Some Curve-billed Thrashers in southeast Arizona give multi-note calls that are difficult to classify.\u00a0 Here’s a bird from a few miles south of Eloy in Pinal County, where I believe the palmeri <\/em>subspecies would be expected:<\/p>\n

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Atypical Curve-billed Thrasher calls recorded south of Eloy, Pinal County, AZ, 2\/22\/2008. Recording by Andrew Spencer.<\/figcaption><\/figure>\n

Here’s some more from the same individual bird:<\/p>\n

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