Sea watch and potential Slaty-backed Gull, 4/2/16

Paul Saraceni

Yesterday morning (7:45-11 AM), April 2nd, Hugh Cotter and I conducted a sea watch from the closed (to vehicles) parking lot at the south end of the Great Highway. Conditions were excellent -- light SW winds, relatively flat seas, overcast, clear visibility out to the horizon.  There was a steady movement of birds (primarily migrating loons), with coastal migration underway. Our numbers are reported below.

There was also a nice gathering of shorebirds and gulls on the beach below and to the south of our position, which we repeatedly scanned. At around 10 AM we picked-up on an interesting first-winter gull in the gathering which showed the following characteristics: bulky goose-like posture with short, dark flesh-colored legs; confined "mascara" look over eye; straight black bill with no real gonydeal angle and a yellowish nail/tip; defined streaking on the nape; bleached wing coverts; dark primaries, secondaries with crescent visible on the primary tips; dark tail with pale edge. In flight with the other gulls the flight feathers were noticeably dark, though we did not see well enough to note if there was a primary window.  Unfortunately the gull was flushed by beach walkers who felt the need to walk right through the roosting gulls and shorebirds, and the gull did not return. We think the gull was a good candidate for SLATY-BACKED GULL, though it's an identification in progress.  We got a series of distant photos, some of which (by Hugh) can be found at the following link:

Comments are welcome.

Here are our seawatch results:

Brant  300+ (multiple flocks flying N, some 30+ birds)
Mallard  1
Greater Scaup  1 m. (flying N)
Surf Scoter  120+
White-winged Scoter  2 (1 m./1 f. flying N)
Black Scoter  9 m., 4 f. (on the water)
Red-breasted Merganser  10 (1,5,1,2,1 flying N)
Red-throated Loon  159 
Pacific Loon  324
Common Loon  4
loon sp.  200
Red-necked Grebe  1 (flying N; looked to be in transitional plumage)
Western Grebe  13
Brandt's Cormorant  56
Double-crested Cormorant  5
Pelagic Cormorant  2
Brown Pelican  2
Turkey Vulture  2 (fly-over)
Cooper's Hawk  1 (fly-over)
Black Oystercatcher  2 (over ocean)
Willet  1
Whimbrel  40+
Marbled Godwit  60+
Sanderling  800+ (impressive flock on the beach)
Least Sandpiper  1 (with Sanderling flock)
Western Sandpiper  2 (with Sanderling flock0
peep sp.  34 (flying N)
Short-billed Dowitcher  6 (on the beach with Godwits/Whimbrels)
LONG-BILLED DOWITCHER  1 (flying with Whimbrel; heard calling "Keek")
Common Murre  12
Pigeon Guillemot  7
Marbled Murrelet  8 (4 pairs, some in alternate plumage)
Mew Gull 13
Western Gull  45+
California Gull  11
Herring Gull 1 1w
Thayer's Gull  1 ad.
Glaucous-winged Gull  2 1w.
potential SLATY-BACKED GULL 1 1w (ID to be confirmed)

California Sea Lion 1 (catching big fish in the surf)
whale sp. 1 (blow seen; likely Gray Whale)

Paul Saraceni
San Francisco

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