Biological Exuberance: Animal Homosexuality and Natural Diversity

RODENTS, INSECTIVORES, AND BATS

RED SQUIRREL

IDENTIFICATION: A medium-sized (10—15 inch), primarily tree-dwelling squirrel with a reddish brown or tawny coat and white underparts, often with a dark stripe on the side. DISTRIBUTION: Canada, Alaska, Rocky and Appalachian Mountains, northeastern United States. HABITAT: Coniferous or mixed forests. STUDY AREAS: Near Ithaca, New York; Manning Provincial Park, British Columbia, Canada; Saint-Hippolyte, Quebec (University of Montreal); subspecies T.h. gymnicus, T.h. streatori, T.h. laurentianus.

GRAY SQUIRREL

IDENTIFICATION: A large (20 inch), tree-dwelling squirrel with a long, bushy tail and gray, grizzled, or buff fur. DISTRIBUTION: Eastern United States, southeastern Canada. HABITAT: Hardwood forests and parks. STUDY AREA: University of Maryland; subspecies S.c. pennsylvanicus.

LEAST CHIPMUNK

IDENTIFICATION: A small, ground-dwelling squirrel with alternating dark and light stripes on back and face. DISTRIBUTION: Yukon to Ontario; upper Midwest; mountainous western United States. HABITAT: Conifer forests, sagebrush. STUDY AREA: Lake Superior State College, Sault Ste. Marie, Michigan; subspecies T.m. neglectus.

Social Organization

Squirrels are generally not gregarious, especially outside of the breeding season, and Red Squirrels defend individual territories throughout the year. The mating system is promiscuous: males and females mate with multiple partners, and only females raise the offspring. Chipmunks are territorial and live in elaborate underground burrows.

Description

Behavioral Expression: Male and female Red Squirrels participate in homosexual mountings, particularly outside of the breeding season. One animal approaches the other from behind (either on the ground or vertically, as on a tree trunk) and grasps it around the waist. The posture used is the same as for heterosexual mating, with the mounter tucking its paws in front of the haunches of the other animal. The mounter often licks, nibbles, or grooms the fur on its partner’s nape or the sides of its neck, and mounting may also be accompanied by play-fighting (harmless “boxing” or kicking sessions) and soft buzzing or mok-calls. Sometimes three animals of the same sex participate in mounting activities at the same time, either alternating among themselves or else all three mounting each other simultaneously (one behind the other in a row). Unlike heterosexual copulation, mounting may be reciprocal, and the mounted animal is usually a more willing participant (although occasionally it will turn around to bite the mounter). In addition, same- sex mounting does not usually involve penetration or pelvic thrusting and is not usually preceded by a courtship chase. Among Gray Squirrels, a similar type of same-sex mounting (with grooming) occurs primarily among younger animals (sometimes among siblings). The activity is often initiated differently from in Red Squirrels, in that the mounting animal makes a bouncing leap onto its partner before grasping it around the waist. Adult male Least Chipmunks also sometimes mount one another.

Occasionally two female Red Squirrels form a bond with each other that includes sexual and affectionate activities and joint parenting. The two share a den (tree hole), follow one another about, and often touch noses or gently nudge each other’s flanks. They also take turns mounting each other, each female nibbling or stroking her partner’s fur while mounting. The pair may raise a single litter of young together; although the youngsters are probably the biological offspring of only one female, both partners may nurse them. In addition, they cooperate in taking care of the young: one such pair was observed leading their lost baby out of a tree and across a street back to their home den. Notably, heterosexual pairs do not usually form in this species: females typically raise young on their own and are generally very aggressive toward other adults that try to approach them.

Frequency: In Red Squirrels, 18 percent of mounts are homosexual; the majority of these are between males, who may participate in same-sex mounts as often as once every half hour outside the breeding season. This is slightly higher than the rate of heterosexual mounting at the same time of the year. Young Gray Squirrels participate in same-sex mounting at a much higher rate, up to 10 times an hour for some age groups (which is more than three times the rate of heterosexual mounting). Among Least Chipmunks, one male was seen to mount another 20 times over four days. Pair-bonding with joint parenting between female Red Squirrels probably occurs only occasionally, although no systematic study has been conducted to determine its prevalence.

Orientation: Adult Red Squirrels that participate in same-sex mounting are seasonally bisexual: outside of the breeding season they engage in both same-sex and opposite-sex mounting, while during the breeding season they mostly participate in heterosexual matings. Females that pair with each other, however, are involved primarily in same-sex activity for the duration of their association, although one and possibly both are functionally bisexual (since they reproduce). Younger animals tend to mount their siblings and therefore are either simultaneously bisexual (interacting with both males and females) or, among males, primarily homosexual (interacting mostly with other males even if females are present). Gray Squirrels are sequentially or chronologically bisexual: juveniles, adolescents, and young adults (up to one and a half years old) show a preference for homosexual activity, while older adults generally exhibit much less same-sex mounting. Since males do not usually start breeding until they are 18 months old, some individuals may be involved exclusively in homosexuality up to that time.

Nonreproductive and Alternative Heterosexualities

Both Red and Gray Squirrels participate in a wide range of nonprocreative sexual activities. Heterosexual mounting outside of the breeding periods is common, especially in Red Squirrels. Since males have a seasonal sexual cycle that renders them infertile at these times (like females), this activity is definitely nonreproductive. In addition, penetration is usually not involved, and REVERSE mounting (females mounting males) also occurs, accounting for about 5 percent of such activity in Red Squirrels. Sexual behavior also takes place in other situations that are not optimal for breeding. Juveniles of both species often participate in mounting or sexual chases, for example, including incestuous activity between siblings or mothers being mounted by their offspring. Interspecies mating chases have also been observed between Gray Squirrels and fox squirrels (Sciurus niger).

During Gray Squirrel mating chases, as many as 34 males may pursue and harass a single female; when cornered in a tree cavity or at the end of a limb, she often defends herself by screaming and lunging at the males and then bolting away. Mounts by males result in full copulation only 40 percent of the time, as females usually escape from a male that is trying to mate with them. In addition, mating pairs are often attacked by other males, who knock the couple from the tree or savagely bite them, in some cases inflicting fatal wounds on the female. When mating does occur, the female copulates with several different males, sometimes as many as eight during a single mating bout. Mating chases in Red Squirrels can involve up to seven males at a time; a female may drag a male mounted on her for some distance or vigorously try to shake him off her back. In Gray Squirrels, sperm coagulates in the female’s vagina following copulation, forming a plug that may prevent inseminations by other males. However, females often remove these plugs, thereby preventing insemination by the male who just mated with them (while at the same time possibly allowing subsequent males to impregnate them). Young Red Squirrels sometimes suffer fatal injuries from adults during territory takeovers, and Gray Squirrel youngsters are occasionally attacked and/or cannibalized by adults. Not all adults participate in breeding: about a third of female Red Squirrels in some populations are nonbreeders, while about 30 percent of male Gray Squirrels do not mate with females each breeding season (and some individuals skip entire seasons).