ML617023818

Age and sex

Adult, Unknown sex - 1

Behaviors

Flying

Media notes

Adult Black-headed Gull in alternate plumage, initially found on 26 March 2024 by Ethan Monk, here photographed in flight by Curtis A. Marantz on 1 April 2024 at the Clifton Court Forebay, Contra Costa County, California.

Observation details

Spotted by Wright in flight shortly after we arrived along the favored section of the levee. Before I was able to get into it, the gull landed on the water among a flock of about 200 Bonaparte's Gulls, but with some effort, we were able to pick it out on the water, and over time, we were able to get good views of this bird, initially on the water at a distance of maybe 300 meters, but once when it flew by at about 100 meters and another time when it was 150-200 away. The light was generally good, with the afternoon sun behind us, but when the bird was in flight the sun was somewhat from the side and the underwing pattern was often shaded. This was a relatively small gull, yet when seen in direct comparison, it appeared to be 20-30% larger than the Bonaparte's Gulls. I also noted that the Black-headed Gull was a bit larger, bulkier overall, and with a somewhat "heavier," less buoyant flight than the other birds. In direct comparison, this bird also had a somewhat larger and stouter bill that was nevertheless relatively slim throughout its length, with little or no gonydeal angle apparent from a distance, and with a tip that seemed blunter than those of the other birds. I further thought the bill would have extended backward on the face to a point near the rear edge of the auriculars, but given the distance from which my observations were made, determining the precise location of the latter was difficult, if not impossible. The forehead was relatively steep and the crown was smoothly rounded, both on a head that appeared proportionately similar to the body as did those of the other birds. The neck was of medium length and it was relatively slim where it met the head. The body appeared to be relatively plump, and maybe more so when the bird was in flight than when it was on the water, it was full-chested, and it sat moderately high on the water. The wings were long and tapering to narrowly pointed tips that appeared to extend beyond the tip of the tail, but because I was unable to see the tail when the bird was on the water, I was unable to determine by how much the closed wings extended beyond the tail. I was alao unable to discern the primary projection even though I was confident that it was relatively long. I saw the tail and belly only when the bird was in flight, but I cannot recall ever seeing the legs or feet. When seen in flight, the wings were at least relatively long and they tapered to pointed tips, but I also thought they were maybe a bit broader than those of the other birds. I also thought the tail was relatively short and having a generally square tip that seemed to be weakly rounded when seen fanned when the bird banked, but I was unable to make out any additional detail. This bird's plumage patterns and coloration were generally quite similar to those of the Bonaparte's Gulls in alternate plumage, which fortunately, represented maybe 10% or less of the total number of these birds. Unlike the vast majority of the Bonaparte's Gulls, this bird had a nearly complete hood that was sharply defined along a line that extended from the sides of the throat back along the lower edge of the face to the rear terminus of the auriculars, where it curved sharply upward to the nape. The result was that the rear edge of the hood was more vertical than on the few Bonaparte's gulls with complete hoods and the back and sides of the neck were entirely white right up to the nape and apparently the rear edge of the auriculars. When seen in good light, this bird's hood appeared to be dark brown as opposed to dark gray or black. The only real contrast noted within the hood was created by narrow arcs of white both above and below each eye that appeared to be more broadly broken before the eye than behind it. I also saw a small spot of white just below the eye on the bird's right side, but I did not see a similar spot on the left side, nor did I see any of the white flecks in the hood that were apparent in photos taken by others in the days prior to our visit. As far as I could determine, the chin, throat, and the lower part of the face through the moustachial, submoustachial, malar, and auricular regions were uniformly dark brown, but the front, sides, and back of the neck were white and unmarked, as were the breast, sides, and what I could see of the belly, flanks, and undertail coverts. As noted above the white on the neck extended right up to the rear terminus of the crown at the nape, and also to the rear edge of the auriculars and the lower edge of the face. Contrasting less conspicuously with the white of the neck, breast, sides, and flanks, the mantle, scapulars, and upperwing coverts were light gray and unmarked. When seen in good light and direct comparison, the light, pearly-gray of this bird's upperparts and closed wings were a shade, or maybe only a half-shade paler than those of the adult Bonaparte's Gulls. I did not note specifically the tertials in the closed wingredients and I may have seen the secondaries in the spread wing, but I thought the latter at least were similar in color to the back and upperwing coverts. I have some recollection of seeing white tips to the tertials, but this recollection is rather weak. I was more confident in my impression that the primary tips apparent in the closed wing were black. This said, when I saw the undersides of the primaries in the partially spread wing when the bird preened, I moved a sharp contrast between what appeared to be mostly white outer-feathers and mostly black inner-feathers. When I saw the fully spread wings on the flying bird, I noted an upperwing pattern like that of the adult Bonaparte's Gulls, with a narrow wedge of white on the outermost two or three feathers that contrasted with light gray on the rest of the upperwing and apparently representing the back, upperwing coverts, tertials, secondaries, and a few inner primaries. I failed to notice in the field if the spread wing had a white trailing-edge or even if the outer primaries had narrowly black tips as they did on the Bonaparte's Gulls, but I suspect both will be apparent in my photos. Whereas the upperwibg patterns of the Black-headed and Bonaparte's Gulls were essentially identical, the underwing patterns of the two were conspicuously different. Whereas the Bonaparte's Gulls had almost entirely white underwings apart from a narrow band of black running across the tips of at least the outer several primaries, on the Black-headed Gull the relatively narrow wedge of white in the outer primaries was accentuated by a conspicuous panel of black on the inner primaries and possibly also the outer few secondaries. I thought the underwing coverts and probably also the inner few secondaries were white, but I cannot now be quite sure about either. To complete the plumage description of the flying bird, the gray back contrasted with what appeared to be an entirely white rump and tail. At least when seen from a distance in good light, the bill was a deep red to purplish-red in color, and appearing not overly different from that of an adult Franklin's Gull in alternate plumage that I saw along the Los Angeles River about ten days earlier. I did not see either a darker tip or a subterminal ring on the bill, but given the distance from which my observations of the bird were made, seeing subtle detail would have been difficult. I likewise noted that the eyes were dark, contrasting with the eye crescents, but not with the overall plumage of the hood, but I was much too far from this bird to discern the color of the irides even in good light. Also, as noted above, I cannot recall ever seeing the legs or feet on a bird that I saw either exclusively on the water or in flight.

Technical information

Model

ILCE-7RM5

Lens

FE 200-600mm F5.6-6.3 G OSS

ISO

160

Focal length

600 mm

Flash

Flash did not fire

f-stop

f/8.0

Shutter speed

1/1600 sec

Dimensions

2300 pixels x 1398 pixels

Original file size

5.1 MB