Heermann's Gull heermannii

(last update: 23-01-2018 )

Coordinators:
John Cant
Mars Muusse

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adult: February

Below you will find a description of Chapter 16 HEERMANN'S GULL Larus heermanni, 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 I: STATUS AND DISTRIBUTION
PART II: FIELD IDENTIFICATION BELOW

FIELD IDENTIFICATION

SIMILAR SPECIES

Uniformly dark plumage, black legs, and red to pinkish bill base diagnostic. First-cycle California Gull and Black-tailed Gull approach Heermanns in overall darkness and have pink, black-tipped bills - but both have pinkish legs, less solidly dark plumage overall with obvious white on tail coverts, bolder pale patterning on wing coverts, and variegated A1 scapulars.

California Gull californicus 1st cycle (1CY), December 30 2011, Fremont, California, USA. Picture: John Cant. Scaps replaced for 2nd gen. First gen flight-feathers. Brown bird.	Black-tailed Gull (crassirostris) juvenile, June 30 2015, Kanazawa, Ishikawa Prefecture, Japan.
California Gull californicus 1st cycle (2CY), January 15 2017, San Leandro, California, USA. Picture: John Cant. 2nd gen scaps, 1st gen flight feathers.	Black-tailed Gull (crassirostris) 1st cycle (1CY), November 11 2014, Chidiwa Unzen city, Nagasaki, Japan. Picture: Nobuo Fukushima. 1CY bird with 1st gen flight feathers (tail, primaries and secondaries).
California Gull californicus 1st cycle (2CY), March 14 2015 , Fremont, California, USA. Picture: John Cant. 1st gen flight-feathers. No coverts were included in the post-juvenile moult (1st PB).	Black-tailed Gull (crassirostris) 1st cycle (1CY), November 08 2014, Chidiwa Unzen city, Nagasaki, Japan. Picture: Nobuo Fukushima. 1CY bird with all the scapulars replaced for 2nd generation feathers. Tertials still juvenile, but several inner and central wing-coverts replaced as well. Post-juvenile moult included also some body feathers, especially the head and flanks. New 2nd gen body feathers are more grey, and are intermixed with the old brown juvenile body feathers.
California Gull californicus 1st cycle (2CY), April 28 2012, Fremont, California, USA. Picture: John Cant. 1st gen flight-feathers. No coverts were included in the post-juvenile moult (1st PB).	Black-tailed Gull (crassirostris) 1st cycle (2CY), February 24 2015, Chidiwa Unzen city, Nagasaki, Japan. Picture: Nobuo Fukushima. 1st gen flight feathers. All scaps replaced, but coverts and tertials still juvenile.

JAEGERS (genus Stercorarius) can be mistaken for Heermann’s Gull, and vice versa, especially because Heermann’s Gulls often chase and kleptoparasitize gulls and terns - but usually this confusion is short lived. Jaegers have white flashes at the base of the underside of their primaries (occasional adult Heermann’s have a white patch on the upperwing, but on the primary coverts), immatures often have distinct barring on their underwings, and most have elongated and projecting central rectrices.

GRAY GULL (Pacific Coast of S. America) averages smaller and slimmer overall with more-slender black bill in all ages, adult is paler and more-uniform gray overall (upperparts paler); adult tail has variable gray basally and lacks bold white tip of adult Heermann’s.

Parasitic Jaeger / Arctic Skua Stercorarius parasiticus, June 18 2012, Brockan, Scotland. Picture: Rolf Nagel. Dark Morph.	Gray Gull Leucophaeus modestus, August 15 2010,  Ica, Peru. Picture: Jean Paul Perret.
Parasitic Jaeger / Arctic Skua Stercorarius parasiticus, July 20 2013, Spitsbergen. Picture: David Nunn. Chasing an Ivory Gull.	Heermann's Gull heermannii 1st cycle (2CY), January 20 2014, San Fransisco, California USA. Picture: Amar Ayyash. 1st cycle Heermann's Gull chase a Common Raven and aggressively harass it in flight, much like jaegers do with gulls and terns.

HABITAT AND BEHAVIOR

Coastal. Sandy and rocky coasts, river mouths, coastal lagoons, fishing harbors. Rarely occurs more than a kilometer inland but ranges over inshore waters, mostly within 50 km of shore. Nests mainly on rocky islands and islets, locally in dense colonies. Nonbreeding birds often in flocks (locally up to a few thousand birds), associating readily with other gulls and water birds. Feeds commonly by scavenging (when often bold and aggressive for its size), also forages in intertidal and surface waters for marine invertebrates, and often seen in association with Brown Pelicans - which Heermann’s Gulls routinely kleptoparasitize.

CONTINUE PART III >>>