Previously I wrote about the variation in immature Ring-billed Gulls in October, using a series of photos from Cape Cod. On 18 April 2010 I devoted a little time (and a granola bar) to watching and photographing immature Ring-billed Gulls in a parking lot in Boston, MA. As always, looking closely at a common bird brings up all kinds of questions. Here is the survey of plumage variation, and I’ll follow-up with some of the questions.
The variation in appearance comes from four main sources, which all interact:
- the intensity (darkness) of feather markings on retained juvenal feathers
- the degree of wear and fading of the feathers (which is related to darkness since pale feathers wear and fade more quickly)
- the extent of dark markings on new feathers on the head and body (which seems to be related to the darkness of the juvenal feathers)
- the extent of the spring molt which may or may not include wing coverts and tertials by this date
In the photo above, the whiter bird in the foreground has excessively worn, whitish wing coverts retained from last summer, clean white head and breast of presumably new feathers grown in the last few months, but is otherwise nearly identical to the bird behind.
In this sample the two birds below with the most heavily worn (and very pale) wing coverts are strikingly different from the darkest bird show in figure 2 above. Presumably these very faded birds were the individuals that had the palest coverts in the fall (e.g. birds 4, 7, and 9 here). These birds now also show a very pale whitish head and breast. The head and breast feathers should have been replaced in the spring molt, while the wing coverts are retained from last summer. So the white head and breast are the result of new, unpigmented feathers, while the white coverts are the result of excessive fading on old lightly pigmented feathers. So maybe birds that produce less pigment in the fall continue that trend in the spring? Or maybe a larger sample size would show no link between extremely faded wing coverts and white heads?
Besides variation in feather color and the intensity of wear and fading, birds can also differ in appearance depending on how many feathers have been replaced in the spring molt. The three individuals below have all replaced some wing coverts and tertials with new – grayish – feathers. A study by Kevin McLaughlin (2000) shows photos of Ring-billed (and Laughing) gulls that have replaced many of their wing coverts and tertials with new gray feathers, and his photos are from the fall. So it’s possible that these birds below actually acquired new gray coverts and tertials in their first post-juvenal molt last fall, although some additional replacement might happen in the spring.
Is a whiter head and neck always associated with extremely pale and faded wing coverts in 1st spring Ring-billed Gulls?
Does Ring-billed Gull have a preformative molt? (Pyle says probably not, my photos indicate otherwise)
Are bare-parts colors and plumage colors linked as immature gulls advance towards adult appearance? In other words, is a gull with more adult-like plumage also expected to have more adult-like bare parts? (This set of birds shows no link)
McLaughlin, K. A. 2000. Variation in First Year Ring-billed Gull. Ontario Birds 19:114-118