Identification: a medium-sized (16 inch) gull with gray back and wings; spotted black-and-white wing tips; bright red bill and legs; white iris.

HERRING GULL

Identification: Similar to Silver Gull except larger (2 feet long), legs pinkish, bill yellow with a red spot, and iris yellow.

Social Organization

Silver and Herring Gulls are usually found in flocks of several hundreds or thousands; they generally form monogamous pair-bonds and nest in colonies containing anywhere from several hundred to tens of thousands of nests.

Description

Behavioral Expression: In both Silver and Herring Gulls, females sometimes form lesbian pairs while males occasionally participate in homosexual mountings. Female pairs may develop between birds who were previously paired to a male, or they may involve birds who have never been paired before. In some cases, single, nonbreeding Herring Gull females visit the territory of a heterosexual pair and court the female, for example by performing HEAD-TOSSING, in which the head is hunched down and then repeatedly flicked upward. The heterosexually paired birds usually respond aggressively, but sometimes this behavior leads to a homosexual pairing the following season. Like heterosexual pairs, homosexual bonds are usually long-lasting and renewed each year: of those Herring Gull females in homosexual pairs that return to the same breeding grounds, 92 percent pair with the same female (compared to 93 percent of birds in heterosexual pairs). Of those that divorce, some remain single while others find a new (female) mate.

Females in same-sex pairs usually build nests and lay eggs. Silver Gull homosexual females generally begin nesting at a younger age than heterosexual females: females paired to other females start on average about a year earlier than females paired to males, and 11 percent of homosexual females begin nesting when they are two years old (heterosexual females never begin this early). Since both females lay eggs, nests belonging to same-sex pairs often have double or more the number of eggs found in nests of heterosexual pairs. These SUPERNORMAL CLUTCHES contain 4 or more eggs in Silver Gulls (compared to 2 eggs for male-female pairs) and 5—7 eggs in Herring Gulls (compared to 3 eggs for heterosexual pairs). Females sometimes mate nonmonogamously with males—or are raped by them (see below)—while still remaining paired to their female partner. Consequently, some of the eggs laid by female pairs are fertile—about a third in Silver Gulls, and 4—30 percent in Herring Gulls. Homosexual parents often successfully hatch these eggs and raise the chicks. Approximately 3—4 percent of all Silver Gull chicks are raised by same-sex pairs, and a further 9 percent of chicks are raised by male-female pairs in which the mother is bisexual. Overall, 7 percent of birds that go on to become breeding adults in this species come from families with two female parents. However, homosexual and bisexual females generally produce fewer offspring during their lifetimes than do heterosexual females.

In both Silver and Herring Gulls, males in heterosexual pairs often try to copulate with birds other than their mates, and in some cases they mount other males. Like females who are mounted by birds other than their mate, male Herring Gulls may respond aggressively to another male’s mounting them.

Frequency: About 6 percent of all pair-bonds in Silver Gulls are homosexual, while nesting attempts by female pairs occur in approximately 12 percent of all breeding seasons. In some populations of Herring Gulls, nearly 3 percent of the pairs are homosexual, while in other populations they are much less frequent, about 1 in every 360 pairs. In addition, approximately 2 percent of courtship behavior by unpaired females interacting with heterosexual pairs is directed toward the female partner. Male homosexual mountings account for 10 percent of the nonmonogamous copulations in Silver Gulls, and 2 percent of the total number of copulations; they are probably much less common in Herring Gulls.

Orientation: In Silver Gulls, 21 percent of females pair with another female at least once in their lifetimes; 10 percent are exclusively lesbian, mating only with other females during their lives, while 11 percent are (sequentially) bisexual, pairing with both males and females. In one study of Herring Gull homosexual pairs, six out of eight females had been in heterosexual pairs the previous year and formed same-sex bonds with each other when their male mates did not return. Of the remaining birds, one paired with a female after her male partner re-paired with another female, while the other had been a single nonbreeder prior to developing a same-sex pair-bond. In addition, female Herring Gulls may show a “preference” for homosexual pairings, since they sometimes re-pair with another female following the breakup of a same-sex bond. In both species, some females in homosexual pairs copulate with males in order to fertilize their eggs, still retaining their primary homosexual bond. Males that initiate homosexual mountings, while functionally bisexual, are probably primarily heterosexually oriented, since they are usually paired to females and rarely engage in same-sex behavior.

Nonreproductive and Alternative Heterosexualities

Large numbers of nonreproducing birds are found in both Silver Gulls and Herring Gulls. About half of adult females and 14 percent of males are nonbreeders in some populations of Silver Gulls; more than three-quarters of all birds die before they reproduce, and 85 percent or more never successfully procreate. Many females that do reproduce nevertheless have extended periods of nonbreeding, up to 16 years in some cases. And about a third of females that lose their mates (through divorce or death) never breed again, sometimes living a further decade as single birds. In Herring Gulls, 4—12 percent of males and one-third to two-thirds of females in some populations are nonbreeders; in other populations, more than a third of all birds do not reproduce in any given year. Two distinct types of nonbreeding females occur in this species: FLOATERS, who are truly single and do not consistently associate with any particular gulls, and SECONDARY FEMALES, who maintain a persistent association with a mated heterosexual pair and even help them defend their territory and raise their young (although they themselves do not breed). Herring Gulls and Silver Gulls also sometimes form polygamous trios, in which the two females are both pair-bonded to one male but not to each other. They often build a “double nest” with two cups in which they both lay eggs.

Several other variant family and pairing arrangements are found in these species. About 5—10 percent of Herring Gull pairs adopt chicks, sometimes even from other species such as the lesser black-backed gull (Larus fuscus ). Herring Gulls occasionally form pair-bonds with adults of this and other gull species as well. Foster parents usually also have young of their own, while some adopted chicks are cared for by more than one foster family simultaneously. Adoption also occasionally occurs in Silver Gulls. In addition, Herring Gulls sometimes form CRÈCHES, in which several adults pool their youngsters and take turns guarding and feeding them. Although most heterosexual pairs are long-lasting, divorce occurs in about 3—7 percent of Herring Gull pairs and 5—10 percent of Silver Gull pairs. Some Silver Gulls have up to seven different mates over their lives, but about a third have only one partner. In addition, many pair-bonds are nonmonogamous: more than 20 percent of all copulations in Silver Gulls are between nonmates, and more than three-quarters of females and one-third of males are “unfaithful.”

Most promiscuous copulations in Silver Gulls are nonreproductive: 11 percent involve incubating (nonfertilizable) females, and many are actually “rapes” or forced copulations in which the female is not a willing participant. As a result, only 7 percent of such matings involve genital contact. Many within-pair copulations are also nonprocreative: more than 30 percent occur during times when the female cannot be fertilized (such as too early before egg laying), and more than half do not involve genital contact or sperm transfer. In addition, about 9 percent of copulations between pair members are forced by the male on the female. Several forms of heterosexual family abuse and adult-juvenile violence have also been documented in Herring Gulls. Males sometimes incestuously mount their own chicks and have even been seen breaking and eating their own eggs. In addition, chicks in both species are often pecked at, pummeled, thrown, shaken, and even killed (and occasionally cannibalized) by other adults when they stray away from home. Among Herring Gulls, being eaten by other Gulls (and sometimes even by one’s parents) can be a significant mortality factor: in one colony, a quarter of chick deaths—more than 300 youngsters—were the result of cannibalism.