Bruce Bagemihl - Biological Exuberance

IDENTIFICATION: Similar to Little Egret but with slaty-gray plumage and a reddish brown head and neck. DISTRIBUTION: Southeastern United States to northern South America. HABITAT: Lakes, marshes, streams. STUDY AREA: Swan Lake, Arkansas; Cliftonville, Massachusetts.

IDENTIFICATION: A large (3 foot long) heron with a gray back, white head and neck, and black “eyebrow” stripe and nape plumes. DISTRIBUTION: Throughout Eurasia and Africa. HABITAT: Wetlands. STUDY AREA: Donana National Park, Spain; subspecies A.c. cinerea.

Herons and Egrets are highly social birds, nesting in dense colonies that may include birds of several different species. During the mating season the primary social unit is the monogamous pair, although several alternative mating systems occur (see below). Outside of the breeding season, they may be found either singly or in flocks.

Behavioral Expression: In all four of these Heron and Egret species, males that are paired to females often copulate with birds other than their mates; in some cases, these involve homosexual copulations with other males who are themselves also paired to females. Homosexual mountings always take place during the mating season. In Little Egrets, mountings between males are most common during the early stages of heterosexual pair formation (before nest-building begins), while in Little Blue Herons at least some homosexual activity takes place during the incubation period, since males have been seen mounting other males that are sitting on eggs. Typically, males mount birds in neighboring nests, although in Little Egrets and Little Blue Herons males may travel to other areas of the breeding colony to engage in “extramarital” or promiscuous copulations (both homosexual and heterosexual).

In Cattle Egrets (and probably the other species as well), homosexual mountings always take place on the mountee’s nest. In a typical encounter, the male seeking an “extramarital” liaison approaches another male, uttering RICK RACK calls (a harsh double croaking sound, also used in heterosexual encounters). The first male then mounts the other bird and crouches on his back; some males only act as mounters in homosexual copulations, others only as mountees, while some males perform both roles. In Little Blue Herons and Cattle Egrets, homosexual mountings may also occur when one male mounts another male who is himself attempting to copulate with a female; sometimes, “pile-ups” of three or four males on top of each other may develop in this way. Usually the mountee is aggressive toward the male mounting him and does not permit cloacal contact. Similarly, male-female “extramarital” copulations are rarely completed, owing to resistance by the female or defense by her mate. In Cattle Egrets, nearly a quarter of all such heterosexual mounting attempts do not involve cloacal contact, while in Little Egrets more than 85 percent of such opposite-sex copulations are “incomplete.”

Frequency: Homosexual mountings can be quite common: in Little Egrets, for example, more than 100 mounts between males were recorded over four months in one colony, with such copulations comprising 5—6 percent of all “extramarital” sexual activity. In Little Blue Herons, homosexual mountings make up 3—6 percent of all copulations outside the pair-bond. Mounts between males represent 5 percent of “extramarital” copulations and 3 percent of all copulations in Cattle Egrets, while in Gray Herons they constitute 8 percent of all promiscuous mountings and 1 percent of the total number of copulations. In 18 percent of “extramarital” copulation attempts on female Cattle Egrets, additional males mount other males in a pile-up.

Orientation: Since males that participate in homosexual activity almost always have female mates, they are technically bisexual (and some birds may even participate in “group” sexual activity involving both males and females simultaneously, as in Little Blue Herons). In Little Egrets, about one-quarter of the male population engages in homosexual mounting, in Gray Herons 5—7 percent of males are involved in such activity, while in Cattle Egrets six out of ten males in one colony participated in same-sex mounting. Some individuals seem to show more of a “predilection” for homosexual behavior than others. In Cattle Egrets, for example, certain males engage in “extramarital” mountings only with males rather than females, while in both this species and in Little Egrets, some individuals participate in same-sex activity noticeably more often than others. In addition, homosexual activity comprises a greater proportion of “extramarital” sexual activity for some males than for others.

As described above, “extramarital” or promiscuous heterosexual copulations occur commonly in all four of these species. In Cattle Egrets, as many as 60 percent of all mountings are by males on females other than their mates, while in Gray Herons such matings account for more than 12 percent of all sexual activity. Nearly a third of all Little Egret copulations are promiscuous. In fact, many copulations in this context are actually rapes, since the female is not a willing participant (although in both Cattle and Little Egrets, females may also consent to such matings). Up to 7 percent of Cattle Egret eggs may be fertilized by a male other than the bird’s (social) father; however, many “extramarital” copulations are nonprocreative, since almost a quarter of all such matings take place when the female is already incubating her eggs. In addition to stepparenting of birds fathered by other males, several other alternative family arrangements occur: Cattle Egret trios of two females and one male may raise a family, while foster-parenting sometimes occurs when females lay their eggs in nests of other birds, including other species of Egrets and Herons.

Several mating behaviors in these species indicate that not all aspects of heterosexuality revolve around breeding. Cattle Egrets sometimes mate when fertilization is not possible, for example during incubation or chick-raising. And up to 14 percent of copulations between pair members may be “incomplete” in the sense that no genital contact or sperm transfer occurs—sometimes because the male is apparently not “interested” in mating even though his female partner is. In Little Blue Herons, some males copulate with females and yet remain “single” (i.e., do not pair-bond with them), while other males never pair with a female during the entire mating season. REVERSE mounts (females mounting males) also occur in Cattle Egrets, and in polygamous trios this sometimes results in a “pile-up” of three birds (one female mounting the second female who is mounting the male).

A number of violent and counterreproductive behaviors can make life harsh for young Egrets and Herons. In Little Blue Herons, infidelity often leads to abandonment of the nest by one or both partners (in part because eggs may be broken during the promiscuous sexual activity). Following a partner’s injury, male Cattle Egrets have been known to destroy their own eggs and desert their mates for a new female. Male Gray Herons also occasionally destroy their eggs by stabbing at them. Nest and mate desertion (especially by females) are common in Little Egrets as well. Often the remaining bird will successfully raise the chicks as a single parent; sometimes, though, the chicks die as a result of desertion. If a single father pairs with a new female, she may kill his nestlings by pecking them to death, so that she can mate with him and raise her own offspring. Cannibalism by siblings or parents sometimes occurs in Gray Herons. In addition, Heron and Egret families are often systematically “pared down” because the youngest nestlings starve to death when they are unable to compete for food; more than three-quarters of all nestling deaths in Little Blue Herons are the result of such “brood reduction.”