Sex liberation in birds (Promiscuity)

Hummingbirds -- Rufous hummingbird (public domain)In North America there are a few bird species that are best called promiscuous, a rather chaotic social structure (according to human standards) in which any female may mate with many males and same is also true for males. This mating system may appear to be a combination of polygyny and polyandry, but polygynous and polyandrous birds make some commitment, however brief, to their mates, but promiscuous birds maintain no associations whatsoever, after mating. The Polygynous Red-winged Blackbird (Agelaius phoeniceus), for example, the male actually helps care for its young; the polyandrous Spotted Sandpiper (Actitis macularius syn. Actitis macularia) female defends a territory upon which the males nest.

It is interesting to note that all of North America’s hummingbirds (family Trochilidae) are promiscuous breeders. The males defend large territories around important food sources and then display to females coming to feed. Females may fly well beyond the territories of local males to find males with which to mate. In these birds males almost certainly never see their offspring or the nest, and most likely will not see the female again. But what energy he displays to each and every female who comes to call! Promiscuous species, which constitute about 6% of all birds, indulge in Indiscriminant sexual relationships, but for a brief duration.  

Similarly males of many grouse species and some shorebirds display on leks (mating grounds used each year) to attract females that depart immediately after mating. The males may subsequently mate with additional females. It is presumed that promiscuous mating systems can evolve only where the advantage of the male remaining with the female to help in raising the young is negligible.

Saltmarsh Sparrows (Ammodramus caudacutus) : the most promiscuous bird

Saltmarsh Sparrow, a small American sparrow, is thought to be the most promiscuous birds in the world. In a study it has been found that 57 out of 60 broods of the bird had at least two chicks with different fathers and at least 97 percent of females were mating with more than one male.

Saltmarsh sparrow (Author - Wolfgang Wander) (GFDL 1.2)

Saltmarsh sparrow (Author – Wolfgang Wander) (GFDL 1.2)

A research by CLAS faculty member Chris Elphick and colleagues shows that this shoreline bird is remarkable for its “extreme levels of multiple mating” and is believed to be the most promiscuous bird in the world. In an article in The Auk, a premier ornithological journal, the scientists described mating patterns that give new meaning to the term “multiple paternity.”

In any one nest, it was impossible to tell who the fathers were of all the chicks without checking DNA.

According to researchers the promiscuity levels seen in Saltmarsh Sparrows are extraordinarily high. Only the Greater Vasa Parrot (Coracopsis vasa) of Madagascar and the Superb Fairy-Wren (Malurus cyaneus) of Australia are known to come close.

It was easy to determine maternity of the chicks, because the mothers sit on the nests, Elphick says: “The tricky part is the fathers.”

Male Saltmarsh Sparrows take no part in chick rearing, so the only way to associate a male with a brood is to catch all the males in an area and conduct paternity tests through DNA analyses.

Reed Bunting (Emberiza schoeniclus)

Reed bunting, a passerine bird in the bunting family Emberizidae, is another bird in which promiscuity is quite rampant. Studies have found that extra-pair males sired roughly half of all of the chicks that were reared in study nests.

It is surprising that promiscuity is quite common in small birds, and both sexes are known to solicit ‘extra-pair’ copulations – those involving individuals other than their mate.

Greater vasa parrot (Coracopsis vasa)

Greater Vasa parrot (Author - AEM) (CC BY-SA 3.0)

Greater Vasa parrot (Author – AEM) (CC BY-SA 3.0)

Greater vasa parrot (Coracopsis vasa), found throughout Madagascar and the Comoros, is one of two species of vasa parrots and has a very unusual breeding biology and mating system. The species lives in loose polygynandrous groups wherein each female, 25 per cent larger than males and is physically dominant, has at least three to eight sexual partners.

In these parrots males have re-evolved a phallus and copulations can last up to 90 minutes. Copulations come in two varieties, short duration lasting only 1–3 seconds, but the long duration averages 36 minutes, with the latter involving a copulatory tie, usually found in mammals such as canines where the animals are unable to part during mating due to the swelling of the penis within the females body.

Bird’s breeding season is uncertain but is probably between October to December. While brooding and chick-rearing, females discard their head feathers and develop bright orange skin coloration. This is the time when they start singing complex songs from perches close to the nest, which attracts males to approach and regurgitate food, which they accept while off the nest. During this period females defend a territory around their nest from other females.

Nelson’s sparrow (Ammodramus nelsoni)

Nelson’s sparrow, a small American sparrow, named after Edward William Nelson, an American naturalist, has unusual breeding system. Males instead of defending territories move around large area of marsh attracting females by singing. Both sexes are promiscuous in this species and do not form pairs like many other birds do; since there are no pairs, males take no part in caring for the eggs or young. Nest built by female is usually a bulky open cup of grass. It is sometimes partially domed over, with lining of finer grass. Incubation and caring of chicks done solely by female.

This bird’s breeding habitat is marshes on the Atlantic coast of Canada and Maine, central Canada, (the Canadian Prairies region and a coastal strip on the south of Hudson Bay) and the north central United States.

Superb fairywren (Malurus cyaneus)

Superb Fairy-wren (male)

Superb Fairy-wren (male)

Fairywrens are socially monogamous, sexually promiscuous and at the same time cooperative breeding species. Though the pairs will bond for life, but both males and females will regularly mate with other individuals; a section of young will have been fathered by males from outside the group.

Since they are cooperative breeders, pairs or groups of 3–5 birds maintain and guard small territories year-round. Groups that are formed consist of a social pair with one or more male or female helper birds that were hatched in the territory, though they may not necessarily be the offspring of the main pair. These helpers help in protecting the territory and feeding and rearing the young. Birds in a group roost side-by-side in dense cover as well as engage in mutual preening, which strengthens social bonding between group members.

Fledglings start feeding on their own after 40 days, but remain in the family group as helpers for a year or more before moving to another group or assuming a dominant position in the original group. In this role they feed and care for subsequent broods and repel predators and intruders. Young are often raised not by the pair alone, but by other males too who also mated with the pair’s female.

American flamingo (Phoenicopterus ruber)

American flamingo (Author - Charlesjsharp) (CC BY-SA 4.0)

American flamingo (Author – Charlesjsharp) (CC BY-SA 4.0)

American flamingos are usually monogamous while selecting nest sites, incubating and raising young; however, extra-pair copulations (EPSs) are frequent. Long-term pairs do not often engage in courtship performances or in-group displays. Pairs often stand, sleep, and eat in close proximity. Courtships are most frequently seen among individuals that change partners over and over again or are promiscuous. 

In these birds there is a variety of pairing relationships. Some have long-term partners throughout the year; others form pairs during periods of courtship and nest attendance. How long a relationship lasts is dependent on many factors, such as addition and removal of adults, maturation of juveniles, and occurrence of trios and quartets.

In most pairs, both individuals usually construct and defend the nest site, but in some cases, one individual undertakes both the duties. If it is trio then the dominant pair begins the nesting process by choosing and then defending the site. For trios with 1 female and 2 males, the subordinate male is tolerated by both individuals and will often become the primary incubator and caregiver of the chicks. Where there are 2 females and 1 male, the subordinate female is tolerated by the male, but often fights with the dominant female. If two females share a nest and both lay an egg, one female will try to destroy the other egg or roll it out of the nest.

In the case of quartets, the 2 females and the dominant male take care of the nest, while the subordinate male remains always around the periphery. In such cases, compared to trios, less animosity is seen between the dominant and subordinate females. Eggs and chicks are attended constantly and equally by alternating parents.

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