Biological Exuberance: Animal Homosexuality and Natural Diversity

Orientation: Some male Humboldt Penguins are exclusively homosexual, remaining with their male partners for their entire lives, or else re-pairing with another male should they lose their original partner. Other males are sequentially bisexual, pairing with a male after having lost one or more previous female mates. Still other males are simultaneously bisexual, engaging in both same-sex and opposite-sex courtship and copulation. Of these, some have a primary heterosexual bond but occasionally engage in homosexual activity with another breeding male: about 47 percent of all same-sex copulations are of this type (as opposed to occurring between bonded partners). In a few cases, the opposite occurs: a male with a primary homosexual pair-bond occasionally participates in a heterosexual copulation. Among King Penguins, birds in same-sex pairs are probably exclusively homosexual for the duration of their pair-bonds (since any eggs that are laid are infertile), and birds exhibit a “preference” for same-sex mates even when unpaired birds of the opposite sex are available. Over the course of their lives, however, most such birds are sequentially bisexual, since following the breakup of a homosexual pair they may go on to form heterosexual pair-bonds and even raise a family. Most Gentoo Penguins that participate in homosexual courtship are probably bisexual, since they court both males and females, albeit with a primary heterosexual orientation (since most go on to breed with birds of the opposite sex). Females that pair with each other are exclusively homosexual for the duration of their bond (which may last for one or both birds’ lives); some females pair with a heterosexual mate after the death of their female partner.

Nonreproductive and Alternative Heterosexualities

As noted above, promiscuous matings by heterosexually paired birds are common in Humboldt Penguins: one-third to one-half of all heterosexual copulations are between nonpair members, and courtship of birds other than one’s mate is also frequent. Promiscuous courtship and copulation occur in King and Gentoo Penguins as well. Even within pairs, sexual behavior may be nonprocreative. In Humboldts, copulation occurs both early and late in the breeding season, when the chances of fertilization are low or nonexistent, while heterosexual mounts (like homosexual ones) sometimes do not include genital contact or sperm transfer (in both Humboldts and Gentoos). Female Gentoo Penguins sometimes mount their mates (REVERSE mounting), while male Gentoos occasionally masturbate by mounting and copulating with clumps of grass. Males have also been observed trying to copulate with dead Penguins.

Several other variations on the lifetime monogamous pair-bond and nuclear family also occur. About a quarter of all Humboldt male-female pairs divorce, often when the female leaves her mate for another male. Divorce also occurs in 10—50 percent of Gentoo pairs, and in some years no pairs remain together. It is especially common in King Penguins, where only about 30 percent of birds retain the same mate from one season to the next. In addition, some King Penguins abandon their mates during the breeding season, and about 6 percent of chicks are reared by single parents (either abandoned or widowed). Humboldts occasionally form trios consisting of either one male and two females or two females and one male; these make up about 5 percent of all heterosexual bonds. In King Penguins, nonbreeding females may associate with a heterosexual pair and help them raise their chick, who recognizes all three birds as its parents; single parenting is also common. Nonbreeders that aren’t part of trios also occasionally feed chicks belonging to other birds, particularly when the chicks are in CRÈCHES. These large nursery groups, sometimes containing thousands of chicks, form while the parents are away. Crèches also occur in Gentoos, where they are often attended by several adult “guardians.” During the winter, King parents are often gone for long periods on fishing trips, and chicks may not be fed for weeks or months at a time. As many as 10 percent of them perish from this prolonged fasting and starvation. Some parents abandon their chicks or eggs (especially in severe weather), and chicks may also be killed in squabbles between their parents and nonbreeding birds that are trying to “kidnap” them. King Penguins also occasionally “steal” other pairs’ eggs.