Bird of the Month: Heermann's Gull
By Hugh Jennings
Scientific Name: Larus heermanni
Length 19 in
AOU Band code HRGU
The Heermann’s Gull (HRGU, not to be confused with HEGU for a Herring Gull) is about 19 inches long. Its genus, Larus, is from the Greek word meaning a ravenous seabird. The species name was given in 1852 by John Cassin for Dr. Adolphus Heermann, a mid-19th century field collector of birds and their eggs, especially in California. This western gull is the easiest to identify. An adult is generally dark gray with whitish head, red bill and black tail.
This bird has a reverse migration, i.e., it moves north for the winter. It nests in western Mexico and then migrates north along Pacific coast in summer and fall. It arrives on the Washington coast in late July or August. Its migration is timed with the movement of Brown Pelicans. When a pelican comes to the surface with a fish, a HRGU is often waiting to try to take the fish out of its pouch. Even though this gull is not large, it is aggressive and harasses other birds to make them drop their catch. It forages in flight over the sea, dipping to the surface or diving into the water for fish. It is usually found along the immediate coast, including beaches, rocky shores, estuaries, lagoons and offshore kelp beds.
Its diet is small fish, crustaceans and mollusks. It sometimes eats eggs of other birds, refuse or carrion. The HRGUs nest in the spring in colonies, some very large, on islands off the west coast of Mexico. The nest is on level ground. It may be in just a shallow scrape in the soil or between boulders. It makes the nest of sticks and grasses, sometimes lined with feathers. There are 2-3 eggs, gray with darker marks. Incubation is by both parents for about 28 days. The young are fed by both parents. The age at first flight is unknown.