Gray Gull Leucophaeus modestus Scientific name definitions

Fernando Medrano, Ignacio Escobar Gutiérrez, and Rodrigo Silva
Version: 2.0 — Published December 23, 2022

Plumages, Molts, and Structure


Gray Gull has 10 full-length primaries, 17–18 secondaries (including 3 tertials), and 12 rectrices; gulls are diastataxic (see 1), indicating that a secondary has been lost evolutionarily between what we now term s4 and s5. No geographic variation in appearance reported (see Systematics).

Gray Gullis a species that takes three years to acquire its Definitive Basic Plumage. The description that follows is based Olsen (2), unless otherwise noted.

Natal Down

The down of chicks has been described as buff to pale gray; it has dark black or gray spots on the upperparts, flanks, side of the head, and throat; the base color of most chicks in one study was pale gray. Spotting varied from moderate to heavy, with the outlines of the spots not well defined (3).

Juvenile Plumage

The body is grayish brown, paler in the face and belly. The mantle and scapulars have narrow pale edges; the coverts and the tertials are darker brown. The primaries and secondaries are very dark brown, the secondaries with narrow pale tips, not broad white tips as in later plumages. The rectrices are very dark brown.

Formative and First Alternate Plumages

Like Juvenile Plumage, but the freshly molted coverts are dark gray. Retained juvenile wing coverts and flight feathers become increasingly brown, faded, and worn. Some feathers likely get replaced twice, indicating the presence of a First Alternate Plumage in at least some birds (see Molts); Formative and First Alternate Plumages similar in appearance except scattered new feathers occur in head and back and except that retained juvenile flight feathers become increasingly bleached and abraded.

Second Basic Plumage

Similar to Definitive Basic Plumage, except for brownish tinge in the head and upper wings. The tail is blackish with narrow pale tips. The white tips to the secondaries average narrower than in Definitive Basic Plumage.

Second Alternate Plumage

Similar to Definitive Alternate Plumage, except that the head is darker and less patterned, and the coverts browner.

Definitive Basic Plumage

The body and upperparts are dull gray. The tail is blackish, and the uppertail coverts are dull gray; the primaries and secondaries are blackish, and the secondaries have white tips to the feathers, which are broader proximally; the white edges of the secondaries are also visible when the wing is folded. The head, from the forehead to the crown, can be whitish-gray, while the rest of the head is a dark dusky-gray, which contrasts with the paler gray of the body, creating a hooded appearance. White eye-arcs contrast against the dusky-gray of the head.

Definitive Alternate Plumage

Similar to Definitive Basic Plumage, except the head is white to grayish-white.

Aberant Plumages

Several records of leucistic individuals exist (4).



Molt and plumage terminology follows Humphrey and Parkes (5) as modified by Howell et al. (6). Gray Gull appears to exhibit a Complex Alternate Strategy (cf. 6, 7), including complete prebasic molts, a partial preformative molt, and partial-to-incomplete prealternate molts in both first and definitive cycles (2; see 8 regarding molt strategies in other Leucophaeus gulls). Study is needed on the occurrence and extent of a First Prealternate Molt.

Prejuvenile (First Prebasic) Molt

Complete, primarily March–June, on or near natal territory. No information on this molt in Gray Gull. In other Leucophaeus gulls, sheaths of scapulars and primaries emerge at 5–8 d of age, upperwing coverts at 8–11 d, secondaries at 9–11 d, and rectrices appear at 13–25 d. Down remains on primary, secondary, and rectrix feather tips until 20 d, on belly, rump, inner legs, neck, and head to 30 d, and on flanks to 40 d; no down at fledging (45–60 d).

Preformative and First Prealternate Molts

Partial to incomplete, primarily August–March. Appears to include most to all body feathers a few to most upperwing coverts, and 1–3 tertials, but no primaries, secondaries, or rectrices. Some back and head feathers, at least, appear to be replaced twice within the first cycle, indicating the presence of both Preformative and Prealternate molts. It may be best to assigned initial replacement of body and wing feathers to the Preformative Molt, the completion of which can overlap with a limited Prealternate Molt of some head and body feathers and perhaps a few wing coverts being replaced for the second time.

Second and Definitive Prebasic Molts

Complete, primarily November–May. The Second Prebasic Molt commences earlier on average than Definitive Prebasic Molt due to lack of breeding constraints; Third Prebasic Molts and those of older non-breeding individuals may also average earlier in timing than those of Definitive Prebasic Molts of breeding birds. Primaries are replaced distally (p1 to p10), secondaries are replaced proximally from s1 and s5 and distally from the tertials, and rectrices are probably replaced distally (r1 to r6) on each side of tail, with some variation in rectrix sequence possible.

Second And Definitive Prealternate Molts

Partial, primarily July–September. Appears to include includes some to most body feathers, no or a few proximal upperwing coverts, often 1–4 tertials/inner secondaries, and occasionally 1–2 central rectrices.

Bare Parts

Bill and Gape

In adults, bill is black; the mouth lining is bright red-orange. The bill is described as dark gray in chicks, with the distal third pinkish-gray; the mouth lining is bright pink (3).


Very dark brown.

Toes and Tarsi

Legs black in adults (2). Legs and feet of chicks are gray (3).


Measurements from Murphy (9). Males are slightly larger than females:

Measurement Mean (mm) Range (mm)
Male wing length 329.2 314–337
Female wing length 318.7 229–337
Male tail length 124 117–131
Female tail length 119.6 116–122
Male bill length 41.8 40–43
Female bill length 39.6 37–41

Recommended Citation

Medrano, F., I. Escobar Gutiérrez, and R. Silva (2022). Gray Gull (Leucophaeus modestus), version 2.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.grygul.02