SPECIES

Heermann's Gull Larus heermanni

Kamal Islam and Enriqueta Velarde
Version: 2.0 — Published April 9, 2020

Behavior

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Locomotion

Walking, Hopping, Climbing, etc.

Walks with alternating gait and uses open wings to hop down from or onto a short perch. Does not climb on vertical surfaces such as tree trunks. Chicks climb on steep surfaces before the onset of flight. Adults climb only if unable to fly, such as when they have been injured.

Flight

Not studied. Like other gulls, a buoyant glider and powerful flier (124).

Swimming and Diving

Swims on water surface by paddling its legs. To obtain food below water while swimming, jumps up into air and then dives into water from airborne position. In addition, makes shallow dives from air.

Self-Maintenance

Preening, Head-Scratching, Stretching, Bathing, Anting, etc.

Preening involves rubbing head and bill over preen gland followed by smearing secretions over body. Scratches head by lifting leg under wing. Stretching involves the extension of one leg and wing on one axis of body while maintaining balance on the other leg. Bathes regularly in salt water, or occasionally in adjacent freshwater ponds, by dipping head and body below water accompanied by vigorous shaking (74). Anting not reported and unlikely to occur.

Sleeping, Roosting, Sunbathing

Little information. Sleeping has been observed to occur in short bouts, as reported for other birds (EV, personal observation). On the San Juan Islands, Washington, birds maintain large resting flocks on rocky beaches and headlands. Also, floating kelp beds and offshore rocks afford lounging substrates (116). No information on sunbathing.

Daily Pattern

No information.

Agonistic Behavior

Physical Interactions

During nesting season, territorial attacks are common mainly between males. These attacks generally occur after some threats are exchanged and consist of locking of the bills and pulling, pecking (mainly directed to head), and grabbing some part of the opponent´s body (generally bill or head, but occasionally also wings or feet) inflicting pressure and sometimes injuries with sharp bill tip. Attacks on conspecific chicks 1–2 weeks of age occur when chicks wander from their nest or are left unbrooded in the nest (18).

Communicative Interactions

In dense breeding colonies, melees often ensue which appear to be outgrowths of territorial fights; sometimes involve 10–12 birds and result in broken or displaced eggs. These displaced or broken eggs become centers of conflict as eggs are either consumed or adults perform displacement activity by pecking at pebbles (19). Birds may utter long notes while leaving the nesting area, or the long call while arriving to the nesting area. This latter call may be answered by the same call issued by several neighboring nesting gulls as well as the mate, and by specific chick calls emitted by their own chicks (121; EV, personal observation).

Territoriality

Defends only the space around the nest site. This varies considerably according to terrain characteristics. In flat areas free of obstacles, the territory is quite small, but if the terrain is uneven and there are rocks or bushes, the territory may increase in area. Colonial birds maintain territories during breeding season, but not at roost sites or during the nonbreeding season. In colonies, nests are evenly spaced (112). See Demography and Populations: Population Spatial Metrics.

Sexual Behavior

Mating System and Sex Ratio

Socially monogamous (126). No information on sex ratio.

Pair Bond

Duration of pair bond uncertain, but banded pairs have been observed to stay together between one to several nesting seasons (EV, personal observation). Both parents feed young at nest. During courtship, females beg for food from the males, in a similar fashion as chicks beg from their parents, who generally regurgitate (121). During early stages of incubation, courtship feeding is part of the nest changeover ceremony (19). Bent (31) provided the following on courtship, "during courtship display, male flies over sitting female; female solicits male by squatting and emitting squeaky call notes,” although he seemed to be describing the food-begging behavior and call issued by the female during courtship, to which the male generally coplies by regurgitating some food. Bent also described: “pairs lock bills and pull one another, as if dancing, before disengaging bills and moving apart; vocalizations accompany all stages of this behavior” (31), which seemed to be a description of territorial fights between males, rather than courtship activities (121).

Extra-Pair Copulations

No information.

Social and Interspecific Behavior

Degree of Sociality

Colonial breeder (see Spacing: Individual Distance, above, for nest densities within colonies). However, within breeding colony segregates from nesting Elegant Tern (Thalasseus elegans), Royal Tern (T. maximus), and Yellow-footed Gull (Larus livens). Highly gregarious during nonbreeding season with roosting flocks of up to 600 birds reported; however, flocks larger than 40 birds seldom reported (106, 86).

Play

Chicks have been observed to play by chasing each other while carrying twigs or small rocks in bill. This occurs among siblings in the first weeks of life, or later on among chicks within a crèche when pre-fledging chicks gather in such groups (121). Another type of play occurs when chicks start practicing flight movements when they reach almost full feather development and are strengthening their flight muscles; they carry out this type of play while running against the wind, sometimes in groups of chicks, or while stationary against strong wind, when they lift themselves vertically in a type of hovering flight. During these times they show excitement and utter a specific chick vocalization (EV, personal observation).

Nonpredatory Interspecific Interactions

Of 29 interspecific aggressive encounters observed between a pair of nesting Heermann’s Gulls and several pairs of nesting Western Gulls (Larus occidentalis) on Alcatraz Island, San Francisco Bay, California, Western Gulls displaced Heermann’s Gulls 21 times, and Heermann’s Gull displaced the larger Western Gulls 8 times (69). Forms mixed foraging flocks during nonbreeding season with Glaucous-winged Gull (Larus glaucescens) and Western Gull when herring school near water surface (116). Also, observed with Brandt’s Cormorant (Phalacrocorax penicillatus), Brown Pelican (Pelecanus occidentalis), and Elegant Tern (127, 71).

Predation

Kinds of Predators; Manner of Predation

Little information. At Isla Rasa, Gulf of California, Mexico, predators on eggs include Common Raven (Corvus corax) and black rat (Rattus rattus); predators on chicks include Yellow-footed Gull, black rat, and Barn Owl (Tyto alba) (128). Predators on adults include Peregrine Falcon (Falco peregrinus) (16, 20, 21, 15). In addition, attacks on conspecific eggs and chicks have been documented (18).

Response to Predators

On Isla Rasa, Gulf of California, Mexico, the daily arrival of a Peregrine Falcon resulted in mass lift-off of breeding birds with most settling on lagoons or inshore waters until the predator passed through the colony (16, 19, 25).

Recommended Citation

Islam, K. and E. Velarde (2020). Heermann's Gull (Larus heermanni), version 2.0. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.heegul.02