The last several days have seen my eBird rare bird alerts blown up by reports of "Slaty-backed Gull" with photos of anything from Iceland Thayer's Gull to the continuing 1st cycle Great Black-backed Gull, or accompanied by brief description along the lines of "continuing bird." Prompted by this, I felt the urge to issue a word of caution on hasty gull identification.
Right now, there seems to be multiple rare Glaucous-winged Gulls and a number of confusing gulls of probable Glaucous-winged Gull ancestry at Warren Lake, Larimer County that are giving even the most experienced gullers some trouble. The candidate for Slaty-backed Gull that Nick Komar reported to eBird last week was reviewed by multiple other experienced gull watchers, and thus far has been deemed inconclusive. I sent the photos to Alvaro Jaramillo, an established gull identification wiz who has found multiple Slaty-backed Gulls in California as well as the state's first Kelp Gull. His response was "It is not a Slaty-backed Gull. Looks better for Herring, but some odd issues that maybe can be explained away, maybe not. But it does not look like a Slaty-backed to me." I myself think the bird looks within variation of some Herring Gull with Glaucous-winged ancestry mixed in. My understanding is that Nick submitted this report in hopes that others would follow up and try to get better photos of an interesting individual, not to entice others to flock over with the false hopes of ticking Slaty-backed Gull off their lifelist. Identifying immature Larus gulls is extremely confusing not only because of physical similarities and variation within individuals of the same species, but because of the multiple plumages they molt through to reach adulthood *as well as* the tendency for several species to hybridize with each other. To complicate things further, recently we've grown to realize that references to season when describing plumages like "1st winter" and "2nd summer" is inaccurate because molt timing varies from individual to individual, thus making assessment even more difficult. I would strongly encourage the use of "Larus sp" in eBird for any large gulls you aren't 100% confident on, and for many of the gulls at Warren Lake, "Herring/Glaucous-winged Gull" seems similarly appropriate. Sometimes eBird filters, particularly with less experienced or active filter editors, will have the "sp" and "/" options flagged when they shouldn't be, so don't be afraid to trip the filter with those taxa. Cordially, David Tonnessen Boulder, CO -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To unsubscribe from this group and stop receiving emails from it, send an email to cobirds+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/cobirds/23a1ed5d-009f-4156-8373-a5b40d11f71c%40googlegroups.com.
