Atlantic Yellow-legged Gull (atlantis)

(last update: October 12, 2011)

Atlantic YLG 4cy February

Below you will find a description of YELLOW-LEGGED GULL (Larus michahellis), as published in one of the best Gull publication: "Gulls of the Americas" by Steve Howell & Jon Dunn.

"we" in the text below refers to the original authors. If any errors occur in this text, please let me know and mail to marsmuusseatgmaildotcom.

PART 1: HERE

THIS IS PART 2:

FIELD IDENTIFICATION

SIMILAR SPECIES

The main confusion species in N. America are Lesser Black-backed Gull and American Herring Gull. Also see hybrid American Herring Gull x Lesser Black-backed Gull and European Herring Gull (under Rarer Species).

Adult Cycle.
Note medium gray tone of upperparts (intermediate between American Herring Gull and Lesser Black-backed Gull), yellowish legs, and, in winter, little or no dusky head streaking and relatively bright bill. Long-call harsher and more grating than American Herring Gull.
LESSER BLACK-BACKED GULL (widespread, but generally rare away from East Coast) overall smaller with more slender bill, narrower and relatively longer wings and shorter legs (especially than nominate michahellis). Upperparts slightly to distinctly darker (Kodak 9-11) with less contrasting and slightly less extensive black wingtips (for example, longer gray basal tongues on P8-P9); molt timing late (by 1-4 months); heavier dusky head and neck streaking in basic retained later.
AMERICAN HERRING GULL (widespread) paler above (Kodak 4-5) with less extensive black wing-tips that often have more white (at least in ne. N. America), flesh pink legs, yellow-orange orbital ring, and, in winter, heavier dusky head and neck streaking, and often a duller and more pinkish bill with more-distinct dark distal marks but no red on maxilla or gape (shown by many Yellow-leggeds). Molts usually l-2 months later than Yellow-legged.

First Cycle.
Atlantis can suggest American Herring or Lesser Black-backed Gull, whereas nominate michahellis can recall Great Black-backed Gull. Mediterranean michahellis, at least, often has fairly extensive PA1 molt that includes upperwing coverts and even tertials by early winter, unlike American Herring Gull.
LESSER BLACK-BACKED GULL perhaps not always safely distinguishable. Nominate michahellis larger and bulkier than Lesser with blockier head, stouter bill, and longer legs; PA1 molt averages earlier and more extensive with new feathers often paler gray and barred, similar to Herring Gull; note indistinct pale inner primary panel (poorly marked birds overlap with Lesser), and tail base averages more-extensively and plainer white at sides than Lesser. Race atlantis structurally more similar to Lesser but averages bulkier and broader winged; first-cycle plumages relatively dark and similar to Lesser; study needed.
GREAT BLACK-BACKED GULL larger and bulkier with stouter bill, but plumage can look similar to michahellis; note narrower tail band more broken by wavy white barring, slightly paler inner primaries, paler greater coverts (with coarse pale barring), and later and less-extensive molt (with much juvenal plumage often retained into winter).
AMERICAN HERRING GULL typically browner overall with less contrasting uppertail coverts and tail; often has some flesh at bill base; inner primaries show as contrasting pale panel; PA1 molt rarely includes upperwing coverts.

Second Cycle.
YELLOW-LEGGED GULL often shows yellowish legs by second summer, when back has moderate to extensive medium gray.
LESSER BLACK-BACKED GULL averages smaller and slimmer than nominate michahellis with more slender bill, generally darker on head and underparts in winter, and upperparts often show darker slaty gray. Race atlantis very similar to Lesser Black-backed but slaty gray on back slightly paler; study needed.
GREAT BLACK-BACKED GULL larger and more massive with stouter, swollen-tipped bill. More “retarded” upperparts often have some dark slaty gray, blackish distal tail band typically narrower and less solid, inner primaries average paler overall, and eyes usually darker.
AMERICAN HERRING GULL typically has more contrasting pale panel on inner primaries, any plain gray on upperparts slightly paler, and tail averages more extensively black (rarely solidly black on Yellow-legged).

Third Cycle.
Much like adult but legs can be fleshy yellow, upperwing coverts mixed with brownish, white wingtip markings reduced. See adult cycle for differences from other species, especially Lesser Black-backed Gull.

RARER SPECIES

Adult Cycle.
Note medium gray to pale slaty gray upperparts, yellowish legs, Herring Gull-like structure.
CALIFORNIA GULL (w. N. America) averages smaller and slighter in build, upperparts similar in tone (Kodak 5-7.5) and wingtips extensively black but eyes dark; legs often greenish yellow on nonbreeding birds; bill has blackish subterminal band (very rarely absent in summer), and winter birds have extensive dusky head and neck streaking heaviest on hindneck.
HYBRID AMERICAN HERRING GULL x LESSER BLACK-BACKED GULL might be quite similar to atlantis Yellow-legged Gull (for example, upperparts around Kodak 7), but field identification criteria unknown. Hybrid European Herring Gull x Lesser Black-backed Gull in Europe typically have orangish orbital ring, yellowish flesh legs, and molt later (more like Lesser Black-backed Gull), so they usually lack streaking when Mediterranean michahellis show streaking in late summer. Hybrids have distinct dusky head and neck streaking in winter, sometimes lost by ]an. or Feb., but this is similar to Cantabrican michahellis and to atlantis; and molt timing of vagrants may differ from source populations.
EUROPEAN HERRING GULL (casual e. N. America). Nominate argentatus averages paler gray above (Kodak 5.5-7), but darkest birds overlap with michahellis, less-extensive black wing-tips often have more white on P9-P10, legs usually flesh pink (but can be yellowish), orbital ring typically yellow-orange, and, in winter, has heavier dusky head streaking and more often shows dark distal bill markings. Molts 1-2 months later than Yellow-legged.
VEGA GULL (w. Alaska) similar in size, shape, and upperpart tone (Kodak 7-8) to nominate michahellis (averages larger and bulkier than atlantis) but has rich pink legs, averages larger white tongue-tips out to P7/P8, and more often has P9 mirror; also note darker eyes.

First Cycle.
CALIFORNIA GULL develops black-tipped, pinkish bill by October; tail mostly black with limited whitish barring at base.
HYBRID AMERICAN HERRING GULL x LESSER BLACK-BACKED GULL might be quite similar to atlantis Yellow-legged Gull, but field identification criteria unknown.
EUROPEAN HERRING GULL has more-contrasting pale panel on inner primaries, duller whitish uppertail coverts and tail base with less sharply contrasting blackish distal tail band. Also averages broader and more-notched pale distal edging to tertials, more evenly barred greater coverts, and usually shows some pinkish at bill base. Nominate michahellis often whiter on head and underparts by early to midwinter, and PA1 often includes some upperwing coverts.
KELP GULL (S. America) averages bulkier with a stouter bill, more-swollen gonys, broader black tail band, darker underwing coverts. PA1 molt averages less extensive with new feathers usually plainer, not boldly barred and checkered; legs average duskier and duller flesh. Note potential differences in primary molt timing of source populations, but these may be modified on vagrants.
HYBRID KELP GULL x AMERICAN HERRING GULL well described; potential differences from Yellow-legged include stouter, bulbous-tipped bill, extensively black tail, duller flesh legs.
VEGA GULL has more-contrasting pale panel on inner primaries, more boldly barred greater coverts, and pale distal edging to tertials averages bolder, more notched; usually shows some pinkish at bill base.
THAYER’S GULL (mainly w. N. America) averages smaller with a less stout bill; PA1 molt later and less extensive (not including upperwing coverts); brownish black wingtips usually have distinct whitish tips and fringes. Upperwing has contrasting pale panel on inner primaries, and outer primaries pale on inner webs; uppertail coverts heavily barred brown and tail mostly dark.
SLATY-BACKED GULL (n. Pacific) averages bulkier and broader winged. Has paler greater coverts, A1 scapulars typically with dark shaft streaks or dark centers. Upperwing shows distinct pale panel on inner primaries, and outer primaries have contrasting pale on inner webs. Tail mostly dark.
WESTERN GULL and YELLOW-FOOTED GULL (both w. N. America) told by larger size and heavier build with stouter and swollen-tipped bills, solidly black tails.

Second Cycle.
YELLOW-LEGGED GULL often shows yellowish legs by second summer, when back has moderate to extensive medium gray to pale slaty gray.
CALIFORNIA GULL averages smaller and slimmer with longer wing projection, slimmer and more parallel-edged bill; legs and bill often have greenish or bluish hues, and bill sharply
two-toned; eyes dark; upperwing has pale panel on inner 3-4 primaries.
HYBRID AMERICAN HERRING GULL x LESSER BLACK-BACKED GULL might be quite similar to atlantis Yellow-legged Gull, but field identification criteria unknown.
EUROPEAN HERRING GULL has more-contrasting pale panel on inner primaries, any plain gray on upperparts slightly paler.
KELP GULL bill averages stouter with deeper gonys, legs typically dull flesh to greenish, any
plain gray on upperparts (obvious by second alternate) is slaty blackish.
HYBRID KEEP GULL x AMERICAN HERRING GULL not well described; potential differences from Yellow-legged include stouter, bulbous-tipped bill, more extensively black tail, duller flesh to greenish legs.
VEGA GULL has more-contrasting pale panel on inner primaries and legs rich pink in second summer, upperwing coverts average brighter and bolder patterning; study needed of distinguishing features.
THAYER'S GULL averages smaller with a less stout bill. Best plumage feature is overall paler upperwings, with pale panel on inner primaries blending into two-tone pattern on
outer primaries.
SLATY-BACKED GULL averages bulkier and broader winged. Plumage usually has some slaty gray in the upperparts by late winter; upperwing has pale inner primary panel and pale inner webs of outer primaries, creating a Thayer’s-like pattern.
WESTERN GULL bulkier and broader winged with stouter, more bulbous-tipped bill; upperparts usually with some to extensive slaty gray; legs flesh pink.

Third Cycle.
California Gull and Vega Gull differ in much the same ways as do adults (see above).

CONTINUE HERE: HABITAT & BEHAVIOUR