Rare Bird Report 26-B-09

Idaho Bird Records Committee
Rarities Report Form

 

Species: Lesser Black-backed Gull (3rd winter)

 

Reporter: Jay Carlisle

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

 

Other Observers: Heidi Ware

 

Date Report Prepared: 3-25-09

 

Date Sighting Occurred:  3-21-09 (note: very likely the same bird seen on 3-24 at Hidden Hollow landfill, Ada County – I’ll submit pictures from both days). 

 

Locality of Observation: Pickle’s Butte landfill, Canyon Co. (also Hidden Hollow landfill, Ada County; see above)

 

Habitat: sand/gravel

 

Conditions: partly cloudy, light breeze; 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

 

Description:  A moderately large gull (larger than nearby Ring-billed and California) with a dark mantle.  The bird was not ‘deep-bellied’ and appeared relatively long & slender.  Bill thicker than those of nearby Californias and mostly yellow with some dusky patterning subterminally; in my best views on 3-24, I was also able to see a hint of red in the gonydeal area.  Also, pale eyes and legs yellow.  Some streaking on the head, especially around the eyes and on the nape.  Seen best in the photo labeled ‘LBBG 5 (3-24)’, there was a two-toned appearance to the mantle such that there was some dark-brownish gray – esp. in the lesser coverts below the mantle - contrasting with the rest of the dark gray mantle.  There was only a single apical spot of white on one primary of the left wing.  The combination of retained brownish feathers in the lesser coverts, bill with much dusky, and the lack of apical spots led me to conclude that this was a bird in 3rd winter plumage.

 

Behavior:  Roosting on sand with other gulls; seen on hills behind dumping area at Pickle’s and in and around puddles at Hidden Hollow.

 

How and when did you positively identify the bird, and what clinched the identification for you?  There had been prior reports of 2 adult Lesser Black-backed Gulls at Pickle’s Butte in the last 2 weeks so this was the ‘bird’ we were looking for.  Thus, once it stepped into view, we both said, “There it is”.  We then went on to study shape, eye color, leg color, and other features to ensure ID.  ID was clinched by moderately large size; long, slender shape; yellow legs; dark gray mantle color; and pale eyes. 

 

How did you eliminate similar species, and what were they?  Similar species include all dark-mantled gulls, including the moderately gray-mantled California Gull, but especially Slaty-backed and Western.  This bird was about 10-15% larger than nearby California Gulls, had a noticeably darker mantle, and had pale eyes.  Both Slaty-backed and Western (darker eye) are larger on average, more bulky in body proportions, have pink legs, and have larger bills.  Also, Slaty-backed adults (not sure how apparent this is in 3rd-winter birds) usually has a more prominent white crescent separating the primaries from the mantle.

 

Experience with this species (and similar species):  I have observed 10 or more Lesser Black-backed Gulls, mostly on the east coast but also in South Dakota.  This is my 2nd in Idaho.

 

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 – from both dates of observation (photos w/o dates in names were taken 3-21).