Lesser Black-backed Gull
Lake Cunningham, San Jose
Santa Clara County, California
4 December 1999
After my class field trip to Palo Alto Baylands this morning, I decided to look
for the Lesser Black-backed Gull at Lake Cunningham. I saw this bird in November 1997 when it was evidently in
2nd winter plumage (Click here for photos and discussion). Now it is nearly an adult, and
I was particularly interested in checking the pattern on the tip of p10. This individual has been somewhat controversial
with the question of eliminating Heuglin's Gull (L. [tamyrensis?] heuglini) being the main issue. Although
I was able to get very close views of this bird, I was unable to get a good enough look at the pattern on the tip
of p10 to make a determination.
I found the bird in the vicinity of the island directly north of the boathouse pier and scoped it for about 45 minutes as it swam and flew around. It then flew to the parking lot on the far side. I drove around and got the bird full frame in binoculars and watched it fly around some more. Eventually I had to leave without being sure of the precise pattern on p10 partly because the feather had not yet grown in fully.
The following description is based on notes taken while watching the bird:
A medium sized adult or near-adult gull, slightly larger than adjacent California Gulls.The mantle was dark gray, comparable to that of Western Gull (L. o. wymani) or American Coot. The body and tail were white. The head was heavily streaked.
The bill was pale yellow at the base with extensive black spotting at the base. At close range, bright yellow slash markings could be seen within the black bill spots. The tip of the bill was bright yellow with an oval shaped red-orange spot on the lower mandible near the gonys. The hook of the bill was paler yellowish similar to the background color of the base. The nostril was perforate. The bill was relatively small, shorter than most California Gulls with a more gradually arched culmen and lacking any obvious gonydeal angle. White maxillary feathering extended out either side, reaching less than half way to the nostril. From in front, this feathering parted at a sharp angle at the base of the culmen.
The eye was pale yellow, gleaming and contrasting strongly with a dark crescent shaped marking in front of the eye. A dusky post-ocular streak extended behind the eye, blending with extensive gray-brown streaking on the face, crown and nape. A darkish post-auricular spot was evident on both sides of the face. Streaking extended down the sides of the neck, but the forehead, chin, throat, and foreneck were white.
A small white scapular crescent was visible, contrasting with the dark mantle. The tertial crescent was white, but blended with the gray tertials and secondaries, not contrasting very sharply. At close range the back and scapulars showed two generations of feathers. Fresh dark ones, and old brownish ones. Thus the bird is still undergoing body molt. The primary projection was very short, with two white-tipped black primaries visible beyond the tertial crescent. These feathers reached only slightly beyond the all white tail, giving the bird a stubby appearance.
In flight it was evident that the bird was molting some of its secondaries. Most of the outermost secondaries appeared shorter than the adjacent innermost primaries and the secondary tips appeared strongly abraded. The primaries appeared to be fresh, but p10 was not visible on the folded wing. I judged that it was still growing in, and that the two visible primaries were p8 and p9 (but see below), each of which were black with white tips but no visible mirror. In flight from below, it appeared that there was a small white mirror on p10, but I could not assess the size of this mirror or its placement with respect to the tip. I also looked to see how many primaries had subterminal black, but it was hopeless as the bird flew around, even at close range. The trailing edge of the wing from below did not have as much dark on the secondaries as I expected, possibly because the secondaries were worn. I definitely needed a camera for times like these.
The entire underparts and the tail were white. The legs were chalky yellow and the feet were pale yellowish-pink. Toenails were black.
Discussion
This bird is clearly either a Lesser Black-backed Gull of the race L. f. graelsii, or a Heuglin's Gull (taxonomy confused) which has never been documented in the Americas. If this bird stays around for another month, it may be possible to get a better determination of the pattern on p10 and the number of primaries with terminal black may be better assessed. The face pattern, overall size, etc. looks fine for Lesser Black-backed Gull to my inexperienced eye.
Additional photos and interesting discussion may be found on Steve Hampton's site here.
Additional note: After viewing photographs and consulting with Mike Rogers, I am no longer sure whether the primaries visible on the standing bird were p8 and p9 or p7 and p8. It is very possible that p9 may not be completely grown. The longest primary extended barely past the tail, suggesting it may have been p8.
A nice photograph of this bird taken by Mike Rogers in December 1998 is on the California Bird Records Committee photo gallery.
--
Joseph Morlan