delawarensis Ring-billed Gull

(last update: 10-03-2014 )

Keith Mueller
Amar Ayyash
Mars Muusse

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2cy Jan
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3cy Jan
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Ring-billed Gull delawarensis 1st cycle (2CY), April 18 2010, Boston, MA. Picture: David Sibley.

See David's site.

The variation in appearance in 1st cycle April birds 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 April pictures (and below), 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.

Below: Two Ring-billed Gulls the same age at about the same stage of molt. The variation in these two birds arises mainly from the extent of dark markings on the newly molted head and breast feathers and the degree of wear and fading on the old retained juvenal wing coverts and tertials.