SLATY-BACKED GULL - HALF MOON BAY, CALIFORNIA

WINTER 2006-2007

Birds from previous years here.

Adult from early January here.

SECOND CYCLE - January 13, 2007

We were finishing up a really fun and successfull Gull Identification Workshop sponsored by SFBBO, in the end we wound up seeing 10 species of gulls in the San Francisco Bay Area in mid-winter which was superb. We ended the day in Half Moon Bay and decided that the light was poor to look at the gulls from the cliff so we walked down to the beach, and had a look at the gulls from there (after seeing about 25 Snowy Plovers). After a bit of time looking at different ages of Western and Glaucous-winged Gulls, and their hybrids one bird facing away from me caught my eye. The back color was the first thing that jumped out, it was noticeably darker than that of the nearby Western Gulls. It also had telltale signs of a Slaty-backed like fine streaking on the head, the mascara look, and the general structure of the bird. After getting all of the scopes trained on the bird, and record photos taken, I studied the bird closely and sure enough it was another Slaty-backed Gull. This one in the second cycle. There were a couple of points which were not classic, like it lacked a pale eye, although it could be seen in the scope that the eye was getting pale. And it also was not a pale winged bird, this one had not worn much yet, and was quite dark on the wing. But these points were minor, and the overall look and details of the bird were superb for Slaty-backed.

First of all it was structurally a plump bodied and short-legged gull, with a relatively long neck and a smallish head. The wings were relatively long, which along with the short legs and waddle when it walked, gave it a look quite unlike the longer-legged Westerns and Glaucous-winged. The photo below shows the bird in a mess of Western, Glaucous-winged and a Herring Gull. The different structure can be seen, as can the contrastingly paler head, darker back, large scapular crescent and largely dark tail.

Below is a closer view, the eye is dark, but paler than the pupil. The bill was short and thick, a feature that has been seen on several of our Half Moon Bay Slaty-backs. There is crisp streaking on the crown and back of the neck, becoming thicker and more blobby towards the lower hind-neck. Some dark surrounded the eye, the "mascara" look classic of Slaty-backed. The bill was becoming pale at the base, at this age Westerns tend to show much more clear yellowish on the bill base. The mantle color could be seen to be a very dark slate-gray, not only darker than that of nearby Western Gulls but lacking the blue tones of that species. The Greater coverts were rather plain, except for the inner ones which along with the medians and lessers showed a more striking pattern than on Western Gulls of similar age. The developing tertial crescent was already wide, and the scapular crescent was more noticeable than on adult Western Gulls, even though it was not entirely white.

Here the bird preens the very dark mantle feathers, and shows the short-legged structure, nice blackish primaries, and crisply streaked crown. The tail can be seen to be entirely dark.

Below, again the short-legged and long-necked structure. This shot shows some of the mascara look around the eye, and the very dark mantle. The tail is dark with marbling at the base. The legs in the field were clearly more bubble-gum pink than the average Western.

A big yawn.

The bird spread the wing and I was not in the best position to capture the wing pattern, ad I also wish I could have seen it from below at this point. Even so one an see a complex pattern on the inner primaries, with darker tips and paler bases as well as white fringes on each feather. The very uniform greater coverts are also clearly seen here. The secondaries are developing a wide white trailing edge, too bad we couldn't get a better look at that. In addition this bird had a good dark belly, contrasting with the pale head and neck.

A slightly open wing shows the paler inner primaries, and the dark but white fringed outer primaries. The inner vanes can be seen to be slightly paler than the outer vanes.

The bird eventually got up with the big mess of gulls that was there, and fortunately I could pick it out in the crowd and I was able to follow it. The bird went north at first and gained altitude before returning our way, high in the air at which point I was able to get some distant pictures in failing light. The bird then cut inland and headed towards the Santa Cruz mountains. Below the gull in warm evening light shows the dark belly, and contrasting white head and neck. The underwing is washed out and there is a dark pattern restricted largely to the tips of the outer primaries (as in a Thayer's Gull).

The last view as it headed inland, showing the very dark back as well as paler inner wing and darker outer primaries.

ADULT - HALF MOON BAY - January 5, 2007.

I went to try and photograph Glaucous-winged Gulls at Venice Beach today and succeeded to a small extent. About 20 minutes into my venture, a bird peeked out above the rest of the gulls showing a greener toned bill, and streaking pattern on the head which led me to believe it was a Slaty-backed Gull. The next ten minutes were an exercise in frustration as the bird sat down, and I needed to cross the creek to get closer, as I succeeded in the latter some dude came walking by and scared nearly all of the gulls. I figured my bird was gone as I could not see it in the group, so I started scanning elsewhere. Then right in the area where he had been, he appeared again. I guess it was hidden by a Western! For the next ten minutes or so I was treated to great views, it allowed pretty good approach. The only problem was that it was somewhat backlit in low light (half an hour before sunset). This bird is presumably not the same probable Slaty-backed sighted by Ron Thorn in December as his showed black on the bill, that bird took off before final details could be assessed unfortunately.

The bird showed the classic crisp streaking on the head and neck, with blobby streaks which were denser on the back of the neck. There was a concentration of dark around the eye, but not as much as on some birds. The eye was not pure yellow, but instead was yellow with some brown flecks and the orbital ring was nice and red. Structurally this bird had some of the classic Slaty-backed traits like the long neck, and small looking head on thick-based neck. It was large bodied with a longer wing than Western, but the legs were not all that short. Shorter than the average Western, but not exceedingly so. Here in this shot the mantle shows to be slightly darker and less blue than that of the Western right in front of it.

Below the arrow points to the white crescent which looks to begin at the white primary tip of the innermost visible primary. This funny crescent is in fact a white subterminal mark on the next longest primary, so a component of the "string of pearls" of Slaty-backed Gull. The white primary tips were larger than on Western Gulls, and the P10 mirror much larger than on most Western. Compared to Western Gull is was only slightly darker in mantle color, but less blue, more neutral gray in color. Not visible here due to lighting is that the streaking on neck was warm colored, almost showing a buffy-brown tone.

Below a close up of the head, showing a reddish tone to the orbital (in some monitors!), the parallel sided bill, and streaking pattern of the nape.

Below the bird from the front, the streaking was more concentrated on the lower neck, on the front. You can just get a hint of red in the orbital here.

The bird from behind showing the concentration of blobby streaks on the back of the neck. You can also see on the left wing the white crescents which create the string of pearls.

This was my first look at the underwing, not a well developed string of pearls pattern, but it was there. Unlike most Westerns this bird had a large mirror on P9, as well as the larger one on P10. You can see that there is a bit of a white crescent inside of the black tip on P8 in this photo. This individual has more extensive black on the underside of P9 and 8 than the classic Slaty-backed, creating a less noticeable string of pearls. It may be that it is a female, due to the small bill size. In general female large gulls have more black on the primaries.

The bird in flight showing the restricted amount of black on the underside of the wing (compared to Western) and the present but not well developed string of pearls pattern (white marks between the gray bases of primaries and black ends. Another feature visible here is the very wide white trailing edge to the secondaries, in fact the inner secondaries are white to the start of the greater coverts!