Rare Bird Report 24-B-09

Idaho Bird Records Committee
Rarities Report Form

 

Species: Thayer’s Gull (adult)

 

Reporter: Jay Carlisle

Idaho Bird Observatory, Boise State University, 1910 University Ave., Boise, ID 83725; jaycarlisle@boisestate.edu

 

Other Observers: Heidi Ware, Louie Quintana, Ileana Cordova (though I was hogging the scope …)

 

Date Report Prepared: 3-8-09

 

Date Sighting Occurred:  2-14-09. 

 

Locality of Observation: Ted Trueblood WMA, Owyhee Co.

 

Habitat: pond with ice

 

Conditions: I don’t remember but no precip; I used Swarovski EL 10x42 binoculars and a Fujinon scope with 20-60x zoom

 

Did you take notes?  not at all

 

Did you consult a field guide or other reference work? after the observation

           

What guide(s) or reference(s) did you consult?

Sibley & National Geographic, Kaufman’s ‘Advanced Birding’

 

Description:  An adult Thayer’s Gull in basic plumage. 

 

The bird was larger than nearby Ring-billed Gulls but notably smaller (maybe by 15-20%) than an adjacent Herring Gull (see pic; at left of candidate) and had a medium-sized yellow bill with a red gonydeal spot.  The mantle was light gray (similar to above-mentioned neighbors) and the bird had black outer primaries with more prominent white terminal spots than the neighboring Herring.  Other features included a rounded head shape, pink legs, and eyes that appeared dark (in contrast, I could easily make out the pale eyes of several adult Herrings).  The head pattern was very dirty and, though hard to quantify, struck me as differently-patterned from the several adult Herrings – as if it appeared more distinctly ‘hooded’.

 

Behavior:  Seen roosting on ice; when it took flight, I lost it among a big group.

 

How and when did you positively identify the bird, and what clinched the identification for you?  The initial clues were the size, dark eyes, rounded head shape, and bill smaller than Herring.  I was 95% sure at the time but wished I had seen the wing pattern (esp. underwing) in flight.  I shared the attached photo with Cliff Weisse who concurred with my ID based on the small bill, rounded headed, and larger white spots (A-spots) on the primary tips.

 

How did you eliminate similar species, and what were they?  Possibilities include Herring (see above), Iceland Gull (similar size/shape but distinctly paler wingtips), and hybrids – especially between Glaucous-winged x Western or Glaucous-winged x Herring (generally larger-billed & bulkier). 

 

Experience with this species (and similar species):  I have observed countless Herring Gulls, 10s of Icelands, and large #s of Thayer’s (including many adults, especially in winter in Oregon, but many inland sightings – esp. 1st W birds - from Idaho to South Dakota) but this was my first adult that I can remember in Idaho.  I have also observed a number of Western x Glaucous-winged hybrids on the west coast – but I am not an expert on gull hybrids.

 

General birding experience: extensive; 15+ years in US and Latin America

 

Were photo(s), video, and/or audio obtained by you? (If yes, please include or attach)    Yes, one poor-quality digiscope (the candidate is the central, distant bird – looking left).