26 March 2014

Baltimore County Black-headed Gull

For three consecutive winters, this adult type Black-headed Gull has presumably been returning to Baltimore County, Maryland, to spend the off-season with a congregation of Ring-billeds:

Black-headed Gull. Baltimore County, MD. 24 March 2014.
I've now observed it every year since its initial discovery in 2011. Little changes have taken place to the wingtip pattern:

December 2011
March 2013
March 2014
It seems like the small black mark on the outer edge of the outer web of P9 was absent in 2013, and now, small traces of it have returned in 2014.

I followed reports of this bird all winter long with hopes of stopping to see it during my annual trip to the East Coast. Amazingly, it had little black on its head all winter long and through the first half of March:
Showing very little markings on the head. 16 March 2014. Photo by Kathleen LaPore Miller.
In the photo above, the head pattern looks no different than it would in December. Here it is 8 days later:
Nearly full hood. 24 March 2014. Photo by Amar Ayyash
Evidently, it's not unusual for BHGUs to hold off on molting into their alternate hoods until March, and then rapidly do so when the process begins -- a reported 10-15% of the hood can be acquired in as little as one day. See this page for more on this fascinating phenomenon.

December 2011
One has to wonder why this individual chooses to associate with a homogeneous flock of Ring-billeds and no other larid species. Does it spend its summers in a Ring-billed colony? Is it hybridizing with Ring-billeds and producing some of the suspected Ring-billed x Black-headed Gulls that have been increasing throughout the Eastern seaboard?

March 2014