ML29799521

Age and sex

Adult, Unknown sex - X

Media notes

This Arctic Tern in adult-alternate plumage was photographed by Curtis A. Marantz on on 3 June 2016 at Piute Ponds, Edwards Air Force Base, Los Angeles County, California. This is one of two birds that had been reported earlier in the day by Jon Feenstra, Adam Searcy, Steve Morris, and Darren Dowell.

Observation details

At least at the level at which I made my observations, I thought these two birds appeared to be identical, in that both were adult Arctic Terns in full, alternate plumage. These were relatively small terns that were conspicuously smaller even relative to the Bonaparte's Gulls that were also standing on the flats and occasionally flying over the pond. I did not attempt to make a direct comparison between the terns and the gulls, but my impression was that the tern stood maybe half the height of the gulls and that their bodies were probably 20-25 percent the mass of those of the gulls. Both birds had relatively short, slim bills that tapered from a base that was relatively shallow to a pointed tip along a culmen that was gently decurved at least across the distal half. I did not attempt to determine the length of the bill relative to field-marks on the face, yet I was confident that these birds had shorter bills than I would have expected from either a Forster's or a Common Tern. I also noted a weakly sloping forehead and a smoothly rounded crown on a head that was unremarkable in size for a Sterna tern. Also evident was that the neck was short and inconspicuous, and that the body was relatively slim, yet with a full-chested appearance, and a posture that was only slightly more upright than horizontal. I noted that the closed wings were relatively long and slim, yet they appeared to fall somewhat short of a conspicuously long tail. We further noted when these birds were standing that their legs were conspicuously short. When seen in flight these birds were small and graceful, with relatively long wings that tapered to pointed tips, and with the bulk of the wing representing the portion between the rest in the wingtip. I again thought the neck was short and inconspicuous, and that the tail extended much further beyond the trailing edge of the wings than the head did relative to the leading edge. Not only was the tail conspicuously long, but it was also deeply forked, with the outer rectrices representing long, tapered streamers. I thought the wingbeats were relatively shallow when these birds were hovering low over the water. The plumage pattern on these birds was pretty typical of an adult, Sterna tern in full, alternate plumage. Both birds had black caps that were well-defined and extending down to about the level of the eye and the base of the bill. I did not however note in the field the point at which the cap met either the eye or the bill. The lower part of the face below the cap was white, as was the throat as far as I could determine. Contrasting with the white of the lower part of the face was a grayish wash that appeared to extend across the breast and sides and at least some degree down onto the belly and probably the flanks. I never did clearly notice if the undertail coverts, or even the lower belly, were white or gray, and I failed altogether to notice the color or pattern on the underside of the tail. Both birds appeared to have light, pearly-gray extending across the back, scapulars, wing coverts, and at least most of the remiges. I did not notice any darkening on the upperside of the wing. The white rump contrasted quite conspicuously with the gray of the lower back, but I was less sure about the pattern or coloration on the upperside of the tail. My impression was that the underwings were almost entirely gleaming-white and unmarked, with the exception of a relatively narrow, dark band along the trailing edge of the wingtip that appeared to represent the tips of most, if not all, of the outer primaries. I thought the dark tips to these feathers was less conspicuous than those on a Common Tern. Far as I could determine, both birds had the bill in its entirety a deep, coral-red. I noted that the eyes were dark, and that they did not contrast with the black cap. I was pretty sure that both birds had reddish legs that were similar but possibly not quite identical in color to the bill.

Technical information

Model

Canon EOS 7D Mark II

Lens

EF400mm f/5.6L USM

ISO

160

Focal length

400 mm

Flash

Flash did not fire, auto

f-stop

f/8.0

Shutter speed

1/1000 sec

Dimensions

2862 pixels x 1738 pixels

Original file size

987.96 KB