ML498801391

観察結果の詳細

Head shape (smooth transitions, fairly flat crown), relatively slender bill, yellow iris, dark wing tips with rectangular mirror on P10, but otherwise slate gray, speckles of transition to winter plumage. Legs difficult as appearing pinkish, yellowish, in variable lighting but can be explained if bird is considered to be in its first year as an adult, ie, entered 3rd yr this summer, as legs pink in earlier years. Size measurements against a Royal Tern in flight - annotated measurement image using Inkscape to measure (.png file) uploaded. The blue lines are the measurement. The black line with arrowed ends is just an add on that goes with the numerical detail and for some reason is shorter. Other numbers are angles. The measurement numbers themselves are meaningless. but the ratio is: 61.36 to 60.76 is 1.01:1, which compares with the ratio of LBBG to RT of 21:20, which is 1.05:1. The gull is worn and the head is slightly downturned. Plus, I'm sure a slightly different set of numbers could be found by redrawing the lines multiple times to sample the accuracy of placing the start and end points. Further, these are living birds not exactly parallel to each other. Nevertheless, a species of 24 - 25 inches would result in eg 24:20, a ratio of 1.2:1, or more. The second annotated image deals with the positions ands transitions in the colours on the underside of the wing which are pointed out in Sibley - Field Guide to Birds of Western North America pages 194 and 197 respectively. Both these images are from screenshots extracted from video. For much better overall images see Nick Ebanks, Matt Southgate, Peter Davey entries.