Bruce Bagemihl - Biological Exuberance

Common Murres and Laysan Albatrosses spend eight to nine months of the year at sea (often in large flocks for Murres). The remainder of the time, they gather at traditional nesting sites in extraordinary densities—Murre colonies, for example, can contain hundreds of thousands of pairs. The mating system is a combination of long-term pair-bonds and promiscuous copulations.

Behavioral Expression: Male Common Murres—usually heterosexually paired—often try to copulate with birds other than their mate, including other males. Homosexual mountings—like heterosexual promiscuous mountings—are usually performed on birds returning to the colony after having been away (for example, while feeding). Immediately upon spotting an arriving male (or female), another male runs toward him, making a harsh, yodel-like crowing sound. He then hooks his neck around the other male and attempts to copulate with him. The other male usually prevents or resists the mounting attempt by standing upright, running away, or directly attacking him. Homosexual mountings also take place during “gang rape” attempts, which occur in 20–30 percent of all promiscuous matings. Groups of males—sometimes as many as ten at a time—gather to try to forcibly copulate with the same female, and occasionally males also mount each other during the ensuing sexual activity.

A similar form of rape occurs among Laysan Albatrosses. Early in the breeding season, males often leave their partner’s side to try to copulate with males or females that are passing through the breeding colony. This is especially true if they momentarily and inadvertently spread and droop their wings (signals usually given by a female before copulation). Groups of five or six males often pursue the same individual, all jostling to mount him or her; typically a male will hook his bill across the neck of the bird being pursued, to throw it off balance. Homosexual mountings are common in these group rape attempts, and “pile-ups” or stacks of up to four males mounted on top of each other have been observed. Rape attempts—whether on males or females—never result in ejaculation, since the bird being mounted always resists the advances of the pursuing bird. A completely different homosexual activity also occurs in this species: occasionally two birds of the same sex perform an elaborate courtship dance with one another. This complex synchronized display involves more than 25 different postures. The two birds stand facing each other, stretching their heads upward during SKY CALLS and SKY MOOS, clap their bills, and bow, strut, and circle around their partner, all the while making a cacophony of clicking, whinnying, wailing, and grunting sounds.

Frequency: At least 5–6 percent of all promiscuous mating attempts on arriving Common Murres are homosexual, and one out of ten arriving males is mounted by another male (compared to three out of four arriving females). Homosexual copulation attempts probably represent 1 percent or less of all mountings (both promiscuous and between pair-bonded birds). In Laysan Albatrosses, rape attempts are frequent before egg laying and probably occur with equal regularity on males and females. Approximately 9 percent of courtship dances take place between two females and 4 percent between two males.

Orientation: About two-thirds of all male Common Murres participate in promiscuous copulations; only a fraction of these engage in homosexual mountings. Male Laysan Albatrosses are as likely to pursue and mount other males as females in their rape attempts. Although it is difficult to draw firm conclusions without detailed study of individual birds, most males that engage in homosexual behavior in these species are probably functionally bisexual, since they are usually already paired with a female (although a few Common Murres who participate in such activity may be unpaired). However, their primary orientation is probably heterosexual since relatively few of their sexual interactions are with other males. The same probably holds for males being mounted by other males: because they usually resist forced mounts by other males, it is likely that most such males are heterosexually oriented. However, most females also resist forced mountings by males, so it is possible that males are reacting negatively to the forced nature of the copulation attempt, as much if not more so than to the sex of the bird mounting them.

As mentioned above, promiscuous copulations occur frequently in these species. About 10 percent of all Common Murre matings are forced copulations between a male and a female other than his partner, and on some days each female is subjected to such a rape attempt nearly every hour. Females usually respond aggressively to such attacks, and their mates also try to defend them, although sometimes an intruding male will actually disrupt a copulation between a mated pair by knocking the male off his partner’s back. In about 15 percent of all promiscuous matings, the female does not react aggressively and appears to cooperate in allowing the male to make genital contact. Female Laysan Albatrosses always resist rape attempts and may be severely injured in the process: one female was attacked by four different gangs of males in ten minutes, losing an eye and sustaining severe wing injuries. However, forced copulations in this species are always nonprocreative since sperm is never transferred. Many promiscuous matings in Common Murres are nonreproductive as well: cloacal contact often does not occur (less than 1 in 200 such matings result in insemination), and during group promiscuous matings, males often mount on any part of the female’s body, including her head. In addition, about 15–30 percent of promiscuous copulations occur outside of the female’s fertile period. The same is also true for sexual activity between mated partners: copulation begins as long as four to five months before the start of egg laying, and half of all heterosexual matings in some populations occur during nonfertilizable periods. In addition, almost a quarter of pair copulations do not involve genital contact. In Common Murres—as in most other birds—females have the remarkable ability to store sperm in special ducts in their reproductive tract, allowing them to inseminate their eggs even when not directly engaging in reproductive copulations.

Other forms of nonprocreative sexuality also occur. Nonbreeding female Common Murres often solicit promiscuous matings from males, while nonbreeding pairs or those who have lost their young (which can make up as much as a third of all pairs) frequently continue to copulate throughout the season. Nonbreeding Laysan Albatross pairs also sometimes engage in copulation. Birds in this species do not reproduce until they are 6–16 years old, even though they mature at one year old and may form pairs fully two years before they actually breed. Similarly, younger Common Murres usually delay breeding until they are five years old, congregating in CLUBS on the tidal rocks beneath the breeding colonies. Such nonbreeders make up approximately 13 percent of the population; among adults, 5–10 percent of birds do not breed each year, and more than a third skip breeding for at least one season during their life. In addition, masturbatory activity—birds mount and “copulate” with clumps of grass—was recently discovered in a closely related species, the thick-billed murre ( Uria lomvia ); it is likely that similar behavior also occurs in Common Murres.