Rare Bird Report 12-B-09

 

Idaho Bird Records Committee Rarities Report Form

 

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

 

            Note: quite possibly the same individual as that reported (& photographed) by Bob Davis at the same location in report # 46-B-08.  I base this suggestion especially on bill pattern, apparent age in consecutive years, leg color and head/chest streaking pattern.

 

Reporter: Jay Carlisle

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

 

Other Observers: none

 

Date Report Prepared: 1-25-09 (updated 3-1-09)

 

Date Sighting Occurred:  12-10-07. 

 

Locality of Observation: Hagerman State Fish Hatchery, Riley Pond, Near Hagerman, Idaho

 

Habitat: pond with rocky islands

 

Conditions: I don’t remember weather; I used Swarovski EL 10x42 binoculars & a Fujinon scope

 

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, Mew, and California) with a dark mantle.  Bill mostly dusky with a brighter yellow tip (and a hint of red apparent within the distal yellow area).  Also, pale eyes and legs pinkish-yellow (more pinkish).  Head and sides of neck heavily streaked.  Head relatively small in comparison to body.  Though difficult to see in the photos, there was a two-toned appearance to the mantle (some dark-brownish gray – esp. in the lesser coverts below the mantle - contrasting with the rest of the dark gray mantle) and there were relatively small white apical spots on the primaries – these features led me to conclude that this was a bird in 3rd winter plumage.

 

Behavior:  Roosting on rocky island with other gulls.

 

How and when did you positively identify the bird, and what clinched the identification for you?  To be perfectly honest, this bird had me very confused.  At first blush, I noticed the dark mantle and pinkish legs and started thinking about Slaty-backed or Western Gulls.  The bill coloration was perplexing and because I was viewing the bird at about a 45’ angle, I had a difficult time judging wing length and body proportions.  It was only after discussions with admitted larophile Cliff Weisse that I started to feel comfortable with the range of variability (leg color and bill patterns) shown by Lesser Black-backed Gulls ….

 

ID was clinched by moderately large size; heavy streaking on head/neck; dark gray mantle color; and pale eyes.  Pinkish-yellow legs and dusky bill seem to fit better with this species than other dark-backed gulls.

 

How did you eliminate similar species, and what were they?  Similar species include all dark-mantled gulls but especially Slaty-backed and Western.  Both Slaty-backed and Western are larger on average, more bulky in body proportions, have pinker 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 first 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.

Images cropped and resized.  Click any image to view original.