[cobirds] Tamarack Eastern Wood-Pewee

Greetings All

On 30 May 2017 I found a pewee singing an Eastern WP like song at Tamarack SWA. In summer 2016, a bird uttering typical Eastern WP vocalizations was present at this location, perhaps in the very same tree. In addition to sounding "just like" an Eastern WP, the 2016 bird  looked "spot on" for an Eastern Wood-Pewee.

So, I let expectation bias roll and identified the bird in 2017 as an Eastern Wood-Pewee

Over the ensuing weeks, a number of people relocated this bird, obtaining good photos (I never saw the danged thing) and audio-recordings. 

Tony Leukering pointed out that the this year's pewee did not look totally perfect for an Eastern in a couple respects. For instance, unlike last years pewee, this year's bird had one (or two) distinct streaks on the undertail coverts. Scouring the Macaulay Library, and excluding areas where both pewees might occur, I could not find an Eastern WP with this mark. 

Additionally, the 2017 bird's vocalizations were similar to those of an Eastern WP, but not quite right. 

So, the awkward topic of hybrid came into mind

Enhancing that possibility is that last year's Eastern WP, when I found it, was in close proximity (15 feet or so) to an adult Western WP that was attending to two recent fledglings. Given the amount of territoriality displayed by other pewees on that date, it seemed almost certain that the female was the mate of the male Eastern WP. This doesn't prove the paternity of those two youngsters, but it does suggest that the father was the Eastern. 

The audio of this year's pewee was sent to audiophiles Andrew Spencer and Tayler Brooks who agreed that the vocalizations were intermediate, just as one would expect from a hybrid.

Given the intermediate visual appearance, vocalizations, and the probably local cross-breeding in 2016 at same location, the most reasonable conclusion is that this year's male was a hybrid Eastern x Western Wood-Pewee. Our intention is to publish an article on this bird, most likely in Western Birds (journal of Western Field Ornithologists).

So, sorry that all reports from Tamarack of Eastern Wood-Pewee from this summer will be invalidated. Like the towhees at Tamarack, it appears that the pewees there must be identified with extra-special care. 

Best Regards

Steven Mlodinow

Longmont CO

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