Aging Gulls

Text by Greg Gillson.
Photographs by Phil Pickering.
Copyright © 2000, all rights reserved.

Second-winter Western Gull

Learning to tell the age of a gull is the first step to identifying one. All gulls go through a sequence of plumages from juvenal to adult. Small gulls (Bonaparte's, for example) make this transition in two years; medium gulls (such as Mew and Ring-billed) make the transition in three years; larger gulls (California and larger) take four years to reach adult plumage. This document tries to explain these complex changes in a simplified, but accurate, way so that birders who have always avoided gull identification can start having more confidence.

Throughout its life a gull goes through spring and fall molts, bringing it into summer ("alternate") and winter ("basic") plumage, respectively. The fall molt (except the very first fall) is a complete molt of all feathers. The spring molt is just the body feathers (not the wings and tail). These molts take place over several weeks, and many individuals seem to be in transition between two plumages. In addition to replacing older feathers through molt, the soft-part (legs and bill) coloration gradually turns into that of the adult.

The common year-around gull on the Oregon coast is the Western Gull. It takes four years to reach adult plumage ("4-year gull"). We describe the plumage changes below, concentrating on the winter plumage, as the summer plumage changes less obviously. In addition, most other gull species summer in the north and only visit Oregon in winter.

The juvenal plumage is the first set of feathers to grown in after the down feathers. This plumage is held only briefly, from about July to October. Juvenile birds in juvenal plumage are brownish, and usually highly patterned with darker bars and checkered patterns.

The plumage sequence progresses as follows: [All photos taken February 2000 at D River, Lincoln Co., Oregon, except juvenile in August 2000.]

juvenile Juvenile plumage. Notice the dark smokey-brown coloration, especially on the face and head. All the wing and back feathers have crisp pale edgings. Chicks begin gaining these first true feathers in July and keep them into August.

Only locally-nesting gulls are seen in juvenile plumage: Western and Glaucous-winged, which nest along the coast, and California and Ring-billed, which nest in the Great Basin and move to the coast in August. Mew Gulls nest as close as coastal British Columbia and may rarely be seen in Oregon as early as August.
larger view
First-winter First-winter plumage begins showing up in September, as juvenile gulls undergo molt and grow in new body feathers. This first fall molt is a partial molt; they retain wing and tail feathers from juvenal plumage. The head and breast of first-winter birds are slightly paler, but otherwise quite similar to the brownish juvenile, including the back.
larger view
Second-winter Second-winter birds are much paler. The key to this age is the adult-gray back and scapulars, but the brownish patterned wing coverts. The base of the bill begins to pale. Eye color approaches that of the adult.
larger view
Third-winter Third-winter birds are similar to adults with adult-gray back, scapulars, and wing coverts. However, there are usually no white mirrors in the primaries. Note especially that the bill usually still has a black tip and there may be a few black tips on the end of the tail feathers. Leg and eye color usually approaches that of the adult.
larger view
Adult winter Adults in winter show yellow bill with red gonys spot. The wing coverts show the adult-gray color of the rest of the mantle. The primaries have white mirrors and apical spots. Each species has its own typical amount of dark streaking on the head or breast. Western Gulls, however, should have very little streaking on the nape in adult winter plumage.
larger view