On October 9th, 2005 I was enjoying the view at First Encounter Beach in Eastham, Massachusetts and watching a small flight of seabirds. A flock of gulls began to gather on the beach close to my car and I found myself more and more engrossed in the plumage variation of Ring-billed Gulls. This first photo shows two first-fall Ring-billed Gulls sleeping, with very different plumage – the one on the left still in full juvenal plumage, while the one on the right has replaced most of the body feathers with first-winter plumage.
Two Ring-billed Gulls of similar age but very different appearance. Eastham, MA, 9 Oct 2005. Photo copyright David Sibley.
This much is familiar to many experienced birders, but on this date I was struck by the fact that these two birds, in two different plumages, are more or less the same age. That is, they were both born in the summer of 2005, but by early October one has advanced into the next generation of feathers, while the other retains all of its juvenile feathers. The difference in appearance is striking, with variation in molt timing combined with variation in juvenal and first-winter plumage colors. Note also the difference in leg color, which seems to parallel variation in bill color.
I photographed about 15 immature Ring-billed Gulls that afternoon, and I have arranged the photos here according to plumage: from full juvenal plumage to the most advanced first-winter plumage. The bird on the left appears below in photo number 1, the bird on the right in number 10.
These were digiscoped with a Nikon Coolpix 4300 hand-held to the 30X eyepiece of a Swarovski AT80 HD telescope. The sky was overcast with some light rain, requiring long exposures and accounting for the blurring in some photos.
1) This is a very dark and fresh-looking juvenile, with mostly dark bill, much as one would expect in late summer. Photo copyright David Sibley.
2) A different juvenile, nearly as dark as 1. Photo copyright David Sibley.
3) Yet another bird still in full juvenal plumage with no replaced 1st winter feathers, but this one is much paler than the first two. The bill has become pink at the base, but not yet with the sharply two-toned pattern of typical first-winter. Photo copyright David Sibley.
4) A very pale and orange-toned juvenile; this bird has replaced a few body feathers with 1st-winter plumage, most conspicuous on the mantle and scapulars, where the new feathers are grayish with bold dark bars. Photo copyright David Sibley.
5) This bird is still mainly in juvenal plumage, but has replaced a few scapulars and a few wing coverts with clean gray 1st-winter feathers. Photo copyright David Sibley.
6) This bird is nearly identical to (7) below in molt stage, but the retained juvenal feathers are darker and less orange. Photo copyright David Sibley.
7) Another with relatively pale and orange-toned juvenal feathers like (4) above, but this one has molted a large patch of scapulars, and the new 1st-winter feathers are relatively clean gray. Photo copyright David Sibley.
8) Most mantle and scapulars new and grayish, but the lowest row are brownish and faded juvenal feathers. Photo copyright David Sibley.
9) An interesting mixture of new 1st-winter feathers with dark bars (on mantle, breast, and flanks), contrasting with retained juvenal feathers with pale orange-brown bars (on nape, belly, wing coverts, and some scapulars). Photo copyright David Sibley.
10) Most scapulars replaced, but some new ones show dusky centers. Photo copyright David Sibley.
11) All scapulars and some wing coverts replaced, most with faint dusky bars. Photo copyright David Sibley.
12) All juvenal mantle and scapular feathers replaced with pale gray 1st-winter feathers, but all showing a "ghost" of the juvenal color pattern. Photo copyright David Sibley.
13) The most advanced-looking plumage seen, with all mantle and scapulars replaced and almost all clean gray (but almost no wing coverts replaced). Note that the bird in photo (11) above is more advanced in molt, with many replaced wing coverts, it just looks "younger" because the new feathers are not as clean gray as (13) here. Photo copyright David Sibley.