This afternoon at about 3:20 I stopped on my way home to check on a large flock of gulls at the far west end of McGuire Road. Fairly quickly my binocular scan picked out a very dark backed gull. I got my scope out in the lee of the van from the wind and saw an adult Slaty-backed Gull. This is the first one since 2009!
Pictures were hard to obtain in the fading light and wind but the dark back really sticks out and if you look closely and add a bit of imagination fairly extensive head streaks can also be seen. Hope it sticks around.
Gord Fraser Valley Birding Administrator eBird Regional Editor (Fraser Valley)
Randy, yes, the heavy streaks would plus a slightly darker back are good clues. At close range the pale eye is another field mark. As one looks at gulls a lot, subtle differences in body shape, bill shape and so forth also provide clues especially with 'textbook' individuals (i.e. a female Thayer's Gull sticks out much more readily than a larger male might).
Watch out for hybrids between Glaucous-winged and Western Gulls. The streaky heads of the Glaucous-winged comes over in the mix but usually the back and wingtips are not very dark.