Bruce Bagemihl, PhD, in his 1999 book Biological Exuberance: Animal Homosexuality and Natural Diversity, stated:
"On every continent, animals of the same sex seek each other out and have probably been doing so for millions of years. They court each other, using intricate and beautiful mating dances that are the result of eons of evolution. Males caress and kiss each other, showing tenderness and affection toward one another rather than just hostility and aggression. Females form long-lasting pair-bonds — or maybe just meet briefly for sex, rolling in passionate embraces or mounting one another. Animals of the same sex build nests and homes together, and many homosexual pairs raise young without members of the opposite sex. Other animals regularly have partners of both sexes, and some even live in communal groups where sexual activity is common among all members, male and female. Many creatures are 'transgendered,' crossing or combining characteristics of both males and females in their appearance or behavior. Amid this incredible variety of different patterns, one thing is certain: the animal kingdom is most definitely not just heterosexual.
Homosexual behavior occurs in more than 450 different kinds of animals worldwide, and is found in every major geographic region and every major animal group. It should come as no surprise, then, that animal homosexuality is not a single, uniform phenomenon. Whether one is discussing the forms it takes, its frequency, or its relationship to heterosexual activity, same-sex behavior in animals exhibits every conceivable variation."
Paul Vasey, PhD, Associate Professor of Psychology and Neuroscience at the University of Lethbridge in Alberta, Canada, stated in the 2002 article "Sexual Partner Preference in Female Japanese Macaques," published in the Archives of Sexual Behavior:
"Multiple lines of evidence indicate that female homosexual behavior in Japanese macaques is a sexual behavior, not a sociosexual one. Additional evidence indicates that female Japanese macaques do not engage in homosexual behavior simply because acceptable male mates are unavailable or unmotivated to copulate.
Patterns of sexual partner choice by female Japanese macaques that are the focus of intersexual competition indicate that females of this species choose same-sex sexual partners even when they are simultaneously presented with a motivated, opposite-sex alternative."
Robin McKie, Science Editor of The Observer, wrote a Feb. 8, 2004 article on "gay" penguins, which stated:
"As gays go, Roy and Silo are not unusual. They cohabit, are affectionate in public and have been inseparable for years. Only their species marks them out. The New York pair are chinstrap penguins.
Every day at Manhattan's Central Park Zoo the two males entwine necks, vocalise to each other and have, er, sex. When offered female companionship, they decline.
Roy and Silo have even displayed urges to procreate, and once tried to hatch a rock. Finally their keeper, Rob Gramzay, gave them a fertile egg from another brood. Tango, their chick, was born later. The pair raised it lovingly. 'They did a great job,' admits Gramzay.
According to a study of the penguins released this weekend in the New York Times, Milou and Squawk - another pair of Central Park's male chinstraps - have started hanging out together, billing and bowing. At the New York Aquarium on Coney Island, Wendell and Cass - male blackfoot penguins - are a devoted couple."
Charles E. Roselli, PhD, et al., wrote in a 2004 article titled "The Volume of a Sexually Dimorphic Nucleus in the Ovine Medial Preoptic Area/Anterior Hypothalamus Varies with Sexual Partner Preference," published in Endocrinology:
"Approximately 8% of rams exhibit sexual preferences for male partners (male-oriented rams) in contrast to most rams, which prefer female partners (female-oriented rams).
We identified a cell group within the medial preoptic area/anterior hypothalmus of age-matched adult sheep that was significantly larger in adult rams than in ewes (females). This cell group was labeled the ovine sexually dimorphic nucleus (oSDN). In addition to a sex difference, we found that the volume of the oSDN was two times greater in female-oriented rams than in male-oriented rams...
Because the medial preoptic area/anterior hypothalamus is known to control the expression of male sexual behaviors, these results suggest that naturally occurring variations in sexual partner preferences may be related to differences in brain anatomy and capacity for estrogen synthesis."