22 July 2015

Great Black-backed with Pseudo-Mirror on P8

Not too many large white-headed gulls develop a 3rd mirror on the 8th primary. Common Gulls regularly do, but Great Black-backeds??

Olsen and Larsson note that about 10% of males and less than 1% of female GBBGs develop a small mirror on P8 (~35mm in males and ~10mm in females). Simply put, it's not commonly seen by most field observers. So I was super excited when I found this bird circling "The Devil's Dance Floor" on Appledore Island recently:

Adult GBBG with triangular-shaped mirror on p8 and two white tips to p10 and p9. Notice the relatively thin white tips to the inner primaries when compared to the mid-secondaries. This is quite different than Western, Slaty-backed and Kelp Gulls.
I'd give up chocolate for the rest of my life to know how old this individual is and how this primary pattern progressed as it aged.

No comments:

Post a Comment