Identification: a small songbird with bright yellow underparts, olive green upperparts, and a black crown (“hood”) and throat in adult males and some females (see below).

Social Organization

During the breeding season, male Hooded Warblers establish and defend territories, attracting mates with whom they usually form pair-bonds. Outside of the mating season, birds migrate south to their winter homes, where the two sexes live largely separate from each other.

Description

Behavioral Expression: Male Hooded Warblers occasionally form homosexual pairs and become joint parents. Same-sex pair-bonds develop early in the mating season when one male is attracted to another male’s territory by his singing. In some cases, this is a male he has previously “prospected” on a visit to his territory during the prior mating season. Once a pair-bond is established, the males focus their attentions on parenting duties. Homosexual couples acquire nests and eggs in a variety of ways. Some pairs may build their own nests: although male Hooded Warblers in heterosexual pairs rarely build nests, at least one bird in a homosexual pair was observed carrying grass fibers to a nest and shaping the cup by repeatedly sitting in the nest and shifting his position. It is not known, however, whether he had built the nest or was simply adding material to a nest built by another pair. As for eggs, some pairs incubate eggs laid by another species of bird, the Brown-headed Cowbird. This species is known as a PARASITE because it always lays its eggs in the nests of other birds, “forcing” them to raise its young. Hooded Warblers are particularly susceptible to parasitism by Cowbirds: in some populations, three-quarters of all nests are parasitized, and Cowbirds appear to prefer Hooded Warbler nests over those of other species. Cowbirds occasionally lay eggs in completely empty nests, so some homosexual pairs of Hooded Warblers may build their own nest and end up tending only Cowbird eggs. Usually, though, a Cowbird adds its egg(s) to a nest that already has eggs (often removing part of the original clutch). Sometimes a Hooded Warbler mother abandons her nest once it has been disturbed this way, and some homosexual pairs may “adopt” such abandoned nests, or else the father of such a nest may re-pair with a male following the mother’s abandonment. At least two male pairs have been observed tending nests that were parasitized, since they each contained both Cowbird and Hooded Warbler chicks. Other male couples probably adopt nests that have been abandoned after attacks by predators. Bluejays and squirrels often prey on Hooded Warbler nestlings, and usually their mother will abandon the entire nest even if only one youngster has been taken. Finally, some homosexual pairs may tend eggs that have been directly laid in their nest by a female Hooded Warbler. In many bird species, females lay eggs in nests belonging to other birds of the same species (this is another form of parasitism); although this rarely occurs in Hooded Warblers, it is a possible source of eggs for homosexual pairs.

A pair of male Hooded Warblers tending their chicks

Once they have acquired a nestful of eggs, male couples typically divide up the parenting duties: one attends to nest repair, incubation of the eggs, and brooding of the nestlings, while the other feeds his mate and defends the territory. Both birds feed the nestlings insects such as crane flies. Although this division of labor is similar to that in heterosexual pairs—females typically build nests and incubate, males defend territories, and both feed nestlings—there are crucial differences. In homosexual pairs, incubating males are often fed by their mate, which occurs only rarely in heterosexual pairs. In addition, one male who engaged in typically “female” parental duties was later observed performing territorial singing (albeit with a song pattern that differed from that of most other males). Nests belonging to homosexual pairs are often lost entirely to predators, but up to 50 percent or more of all heterosexual nests are lost in the same way. The male couples that have been followed over a longer time do not appear to re-pair with the same mate in subsequent breeding seasons; their divorces may be related to the loss of nests to predators. Heterosexual divorce is also common in Hooded Warblers, with as many as half of all male-female pairs failing to remain together, perhaps also due in large part to loss of nests. It is possible as well that divorce is simply a general feature of pair-bonding in this species (heterosexual or homosexual) independent of nest losses, or that the particular pairs being studied happened to end in divorce without this being indicative of a larger pattern.

Some female Hooded Warblers are transvestite, having the same black hood that males do. In fact there is a continuum of transgendered physical appearance in females: some have no black feathers on their head at all, some have an intermediate amount with a black “bib” around the throat, while others are almost indistinguishable from males. In addition, a few females can sing (typically only males in this species are able to sing). Transgendered females usually mate with males and raise young just like nontransgendered females.

Frequency: The overall incidence of homosexual pairs in Hooded Warblers is not known, since no widespread, systematic study has yet been conducted to determine their prevalence. However, in one population observed over three years, 4 percent of the pair-bonds (3 of 80) were between males. Although overt sexual behavior has not yet been observed between such pair-mates, heterosexual copulations (both within-pair and nonmongamous) are rarely seen in this species either; it is possible, therefore, that homosexual copulations do take place. Among females, plumage transvestism is a regular occurrence, as about 59 percent of females have some degree of malelike black feathers on their head: 40 percent have only a slight amount, 17 percent an intermediate amount, and 2 percent have a nearly complete black hood.

Orientation: Some male Hooded Warblers appear to be exclusively homosexual, pairing only with males; if they divorce a male partner, they re-pair with another male in subsequent breeding seasons. These males often perform parenting duties typically associated with females in heterosexual pairs. Other males, however, are bisexual, alternating between homosexual pairings and heterosexual ones in different breeding seasons.

Nonreproductive and Alternative Heterosexualities

As mentioned above, heterosexual divorce is common in Hooded Warblers, as are a number of other variations on the nuclear family and monogamous pair-bond. About 4 percent of males form trios, mating with two females who both nest simultaneously on the male’s territory; 6 percent of males are nonbreeders, and some females remain single as well. Among paired birds, promiscuous copulations also occur very frequently: 30—50 percent of all females copulate with males other than their mates (usually neighboring males), and more than a third of all nestlings in some populations are fathered by a bird other than their mother’s mate. In addition, males sometimes adopt young birds from neighboring families whose own parents have finished caring for them; adoptive fathers typically feed these youngsters along with their own nestlings. The adopted birds are usually not genetically related to their foster fathers, i.e., they are not the result of promiscuous matings by the bird who adopts them. Single parenting is also a regular occurrence in Hooded Warblers: once their young can fly, parents usually separate and each takes care of half the brood (unless the female begins a second family, in which case the male will assume responsibility for all of the youngsters). In fact, single parenting is generally more extensive and longer-lasting than male-female coparenting in this species. Nestlings receive biparental care for only eight or nine days, while single parenting can last for three to six weeks and involves feeding rates that are three to five times higher than that of coparents. As a result of separation of mated pairs, males and females are together for only about one month out of the entire year. During the winter, the two sexes occupy largely segregated habitats, with males preferring forests and females scrub areas.

CHAFFINCH