Heermann’s gull in Los Cabos

How to recognize it

A medium-sized gull that is dark all over: slate-gray body, darker wings and a black tail. The bill is bright red with a black tip and the legs are black. Breeding adults have a clean white head; outside the breeding season the head is streaked gray-brown. Young birds are a fairly uniform sooty chocolate brown, without the heavy mottling of other young gulls, with a pale pinkish bill tipped dark. It takes about four years to reach adult plumage.

Biology

Heermann’s gull breeds almost only in the Gulf of California. About 95% of the population, some 130,000 pairs, nests on Isla Rasa, a flat island of about 56 hectares in the Midriff region of the northern Gulf; the next-largest colony, on nearby Isla Cardonosa, has about 4,000 pairs, and smaller colonies extend along the Mexican coast as far as Nayarit. Gulls arrive on Rasa in mid-February and lay 1 to 3 eggs, packed at densities of up to 110 nests per 100 m². They start breeding at about four years old. Egg collecting pushed the species down to an estimated 55,000 pairs in 1975; the island became a seabird sanctuary in 1964, introduced rodents were removed in the mid-1990s, and the species now numbers around 350,000 birds.

It lives mostly on small schooling fish: in the early 1980s Pacific sardine made up 60 to 97% of its diet, along with northern anchovy. It is also a pirate. It steals fish from brown pelicans, sometimes straight from the pouch, and from terns bringing food to their chicks; one study found that about 13% of pelican dives drew a theft attempt. After nesting, most of the population heads north along the Pacific coast, reaching British Columbia, while others disperse south along the Mexican coast as far as Guatemala.

Seeing them from the boat

Heermann’s gull is on the Defenders of Wildlife list of common birds of Los Cabos. Look for it on beaches, at the marina and near fish-cleaning stations, and around brown pelicans diving on bait close to shore, where it waits to snatch a fish. It is a coastal bird that rarely goes far offshore, so you are much more likely to see it in the bay than on the marlin grounds. Sighting records (GBIF, iNaturalist) show it most often around Cabo from December to March, with another bump in July as birds disperse after nesting; in spring many adults are at the breeding colonies hundreds of kilometers north, and October–November records are scarce.

Gulls sometimes grab a bait or a fish being reeled in. Don’t cut the line, because trailing line can entangle the bird. Bring it in slowly, have someone control the head and bill, cover its head with a cloth to calm it, cut the barb before backing the hook out, remove all the line and release it. Don’t feed gulls fish scraps. Because it is a protected species in Mexico, a seriously injured bird should be reported to PROFEPA.

Rules & conservation

Don't confuse it with

The yellow-footed gull, the big resident gull of the Gulf, is much larger, with a white head and underparts, a heavy yellow bill with a red spot and bright yellow legs. The western gull of Baja’s Pacific coast is also large and white-headed, with pink legs. Young big gulls are mottled and checkered brown with dark bills, while a young Heermann’s is a smooth, even dark brown with a pale, dark-tipped bill and black legs.

Questions

By Max VargasTop Anglers, Cabo San Lucas · international judge at big game fishing world championships · reviewed October 2026

Sources

• Velarde 1999, breeding biology of Heermann’s gulls on Isla Rasa (The Auk)
• Birds of the World, Cornell Lab: Heermann’s gull
• Seabird diets provide early warning of sardine fishery declines in the Gulf of California (Scientific Reports, 2013)
• Heermann’s gull life history under present oceanographic variability (The Condor, 2018)
• Velarde & Findley 2026, diets of three larids nesting on Isla Rasa (Marine Ornithology)
• Demographic history of Heermann’s gull from the late Quaternary to present (The Auk, 2017)
• Cornell Lab, All About Birds: Heermann’s gull identification
• Defenders of Wildlife: quick guide to the common birds of Los Cabos, BCS
• NOM-059-SEMARNAT-2010, 2019 update (DOF)

Top illustration: Top Anglers. Photos: iNaturalist contributors, credited on each photo.