Some of this may be due to observer-bias, but also likely is a rapid turnover rate as the species moves out at sea or up and down the coast in search of a food source.
Similar to when I wrote about the status of LBBG in Birding magazine a few years ago, the age distributions are still consistently in favor of young birds - mostly 1-2 year-olds in the midst of complete molts. Rarely do I find evidence of definitive adults being recorded in the breeding season.
It seems to me, however, that a percentage of younger birds may be going unnoticed in Herring and Great Black-backed flocks, especially as one moves north into New England where the latter two species are found in greater numbers.
|A mixed flock of Herrings, Great Black-backeds and Lesser Black-backeds. How many LBBGs do you see in this photo?|
|A not so uncommon summer sighting on the mid-north Atlantic coast, a Herring, Lesser Black-backed and Great Black-backed, all seen together. Provincetown, MA. 18 July 2015.|
Earlier this month I spent a total of 3 days surveying gulls at two sites along the northernmost point of the Cape Cod peninsula: Herring Cove & Race Point Beach in Barnstable County, Massachusetts. These two locations hold an impressive diversity of summer gulls, and one need not look any further than recent eBird reports to verify this. Surprisingly though, high counts of Lesser Black-backed Gulls reported at these sites in early July 2015, by reliable observers who regularly count birds at these locations, were 5 and 8, respectively. Below are my high counts.
Herring Cove. 18 July 2015. 27 Lesser Black-backed Gulls
(22 1st summer, 4 2nd summer, 1 3rd summer).
Race Point Beach. 19 July 2015. 39 Lesser Black-backed Gulls
(21 1st summer, 13 2nd summer, 3 3rd summer, 2 4th summer types).
I don't mean to be critical of the experienced birders that frequent these sites as I'm sure they're perfectly capable of identifying sub-adult Lesser Black-backeds. But as one birder put it to me, the attitude in the summer months is much like this: "I'll just add any gulls I didn't feel like looking at to the HERG count".
|GBBG, HERG, GBBG, LBBG. Barnstable County, MA. 19 July 2015.|
|Advanced 2nd summer type LBBG, 4th summer type GBBG and 1st summer LBBG.|
|4th summer GBBG (Appledore Island Black 9M0, born in 2012) and 1st summer LBBG.|
|1st summer LBBG and 1st summer GBBG.|
|First summer LBBG and GBBG|
|Two 3rd summer type LBBGs, one 1st summer type and an adult type HERG. The second bird from the left is big-billed, big-bodied and has noticeably pale upperparts. I do suspect it may be a LBBG x HERG hybrid (so called Appledore Gull).|
|Very similar in plumage aspects, these 1st summer cousins are readily told apart by size and structure.|
|Both this bird and the individual below appear to be 4th summer types, and not yet definitive adults.|
|Perhaps the maturest LBBG I've seen in July on the Atlantic coast. Barnstable County, MA. 19 July 2015.|
And now the answer to the "number of LBBGs" from the photo in the beginning of this post:
|A total of 8 LBBGs in this frame. Barnstable County, MA. 19 July 2015.|