- 18.1–20.9 in
- 40.9–45.3 in
- 13.1–22.7 oz
- Goéland de Heermann (French)
- Gaviota de Heermann, Gaviota mexicana (Spanish)
- The Heermann's Gull, like many other gulls, frequently steals food from other birds. The Brown Pelican is a frequent victim. An adult Heermann's Gull is most likely to try to steal food from an adult pelican, and an immature gull is more likely to steal from an immature pelican.
- The Heermann's Gull is the only North American gull that breeds south of the United States and comes north to spend the nonbreeding season. After breeding is over in July, the gull quickly comes north all the way to southern Canada. It heads back southward by December, and most breeders are at the breeding islands by March.
- Perhaps as a result of the increasing populations in Mexico, several attempts have been made by Heermann's Gulls to breed in California. The first was on the island of Alcatraz. So far these attempts have been unsuccessful, but eventual successful nesting is expected.
- The oldest recorded Heermann's Gull was a female, and at least 24 years old when she was caught and released in Oregon in 2009. She had been banded in Mexico in 1985.
- Nests on arid offshore islands.
- Winters along coast and out to sea.
- Rarely inland.
Small fish, marine invertebrates, lizards, insects, refuse, and carrion.
- Clutch Size
- 1–3 eggs
- Egg Description
- Pale bluish gray to olive, with brown blotches.
- Condition at Hatching
- Semiprecocial with eyes open. Covered in down, grayish white mottled with dusky on back, pinkish buff on head and underparts.
Nest a shallow depression in the ground, or an open platform of sticks, dry grass, and weeds. Nests in colonies among boulders or nestled in grass.
Picks food from surface of water, plunges into water to pursue fish. Hovers and dips over waves. Steals food from marine mammals and other birds.
There is little information on Heermann's Gull population trends. The North American Waterbird Conservation Plan estimates 350,000 breeding birds on the continent and lists it as a Species of Moderate Concern. These gulls rate a 16 out of 20 on the Continental Concern Score. Heermann's Gull is on the 2016 State of North America's Birds' Watch List, which includes bird species that are most at risk of extinction without significant conservation actions to reverse declines and reduce threats. The species is vulnerable to human disturbance because 90-95% of the total world population breeds on one island, Isla Raza. The island was made a wildlife sanctuary in 1964, and populations have increased since then. Heermann's Gull is listed as Near Threatened on the IUCN Red List.
- Islam, K. 2002. Heerman's Gull (Larus heermanni). In The Birds of North America, No. 643 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
- BirdLife International. 2012. Larus heermanni. The IUCN Red List of Threatened Species 2012: e.T22694296A38862429.
- Kushlan, J.A., et al. 2002. Waterbird conservation for the Americas: the North American Waterbird Conservation Plan, version 1. Waterbird Conservation for the Americas. Washington, DC.
- North American Bird Conservation Initiative. 2016. The State of North
America’s Birds 2016. Environment and Climate Change Canada: Ottawa, Ontario.
- USGS Patuxent Wildlife Research Center. 2016. Longevity records of North American Birds.