Herring gulls are almost always monogamous, with rare cases of 1 male and 2 females occupying a territory and incubating 1 or 2 nests. The secondary female rarely achieves breeding success. Pairs are formed on the male's territory or in loafing areas. Males and females choose territory for egg-laying together, once they have paired. Males regurgitate food for females before eggs are laid. Any late arrivals pair only after early-nesting pairs have already begun breeding. Pair bonds are maintained for the life of both partners. If a male fails to provide enough food to the female during egg formation or if the partners fail to synchronize their eggs (leaving eggs unattended and often lost or eaten), the pair may separate. Within the colony, pairs nest as far apart as space allows.
There are no displays specific to courtship, but females usually approach males in a hunched posture, producing a begging call. The male responds by assuming an upright posture or mew-calling (see Pierotti & Good for more information on specific types of calls). Head-tossing occurs repeatedly by both male and female and the male regurgitates food for the female; if she eats it, copulation often happens immediately. Otherwise, the female may walk away and prevent copulation. Males jump on females' backs with wings outspread in order to copulate. Mate-guarding is most intense in the week prior to egg laying. Males whose mates have already laid eggs may attempt to force copulation on neighboring incubating females; no such attempt has ever been observed as successful.
Mating System: monogamous ; polygynous
Herring gulls breed during spring, pairing around mid-March and laying eggs by mid-May. Adults breed beginning around four years of age, although breeding for the first time at three or five years of age is also observed. Females take 4 to 6 days to lay 3-egg clutches, and the eggs are incubated by both parents for about four weeks. Chicks are able to leave the nest on foot after just one day. Chicks fledge after about six weeks and are fed in the territory where they were born for until about 12 to 15 weeks old. Occasionally, they are cared for by parents off territory for as long as 6 months.
Breeding interval: Herring gulls breed once yearly.
Breeding season: Herring gulls breed from April to June, including nesting and copulation.
Range eggs per season: 1 to 3.
Average eggs per season: 3.
Average time to hatching: 30 days.
Range birth mass: 60 to 75 g.
Average fledging age: 6 weeks.
Range time to independence: 24 (high) weeks.
Average time to independence: 12 to 15 weeks.
Average age at sexual or reproductive maturity (female): 4 years.
Average age at sexual or reproductive maturity (male): 4 years.
Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)
Both male and female parents incubate eggs. The female spends more time incubating than the male does, and incubates at night. The male spends more time away from the nest, procuring food for the female. Many parents remove broken shells once chicks have hatched. Chicks are semiprecocial at hatching, with gray and black down and open eyes. After one week they are able to run around on their own. Chicks are protected by both parents and, during dangerous weather, are brooded until 10 days of age. Chicks fledge at about 6 weeks of age and are fed by parents on parental territory until they are 11 to 12 weeks old; so long as chicks continue to beg, they may receive food from parents until about 6 months of age. Males feed more often before fledging, females feed chicks more after fledging. Studies have found that herring gull parents can feed lead-poisoned chicks, which are generally lighter than normal chicks when studied in the laboratory, enough so that the chicks maintain a close-to-average weight (Burger and Gochfeld, 2000). Chicks are fed regurgitated food that consists of small prey such as small fishes, insects, and earthworms.
Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female)