Competing Females and Caring Males. Polyandry and Sex‐Role Reversal in African Black Coucals,Centropus grillii

Abstract

Most species of birds show bi-parental or female-only care. However, a minority of species is polyandrous and expresses male-only care. So far, such reversals in sex roles have been demonstrated only in precocial bird species, but there was suggestive evidence that such a mating system may occur in one altricial bird species, the black coucal, Centropus grillii. In a field study in Tanzania we investigated whether black coucals are sex-role reversed and polyandrous. We found that males were mated to one female, rarely vocalized and provided all parental care from incubation of eggs to feeding of young. In contrast, female black coucals were about 69% heavier and 39% larger than males and polyandrous. They spent a large proportion of time calling from conspicuous perches, defended breeding territories, did not help in provisioning young and had a higher potential reproductive rate than males. We conclude that the black coucal currently represents the only altricial bird species with sole male parental care and a classical polyandrous mating system. High nest predation pressure and small territory sizes due to high food abundance may have been important factors in the evolution of sex-role reversal and polyandry in this species.

Song amplitude and body size in birds

“…This species is sex-role reversed, i.e. females defend breeding territories and advertise territory ownership by song, whereas the smaller males rarely vocalise and provide all of the parental care (Goymann et al 2004). In their analysis of the female singing behaviour, Geberzahn et al found no correlation between the acoustic characteristics of the female solo songs and the birds' body size.…”

A single functional testis and long deferent duct papillae: the peculiar male reproductive tract of the classically polyandrous, sex-role reversed Black Coucal (Centropus grillii)

“…Presumably, this is assisted to some degree by the eversion of both male and female cloacae during copulation (involving the strong circum-cloacal musculature). In Black Coucals, as in other avian species, males appear to have a greater share in establishing close contact of male and female cloaca, as their cloacal opening, the ventus, is elevated to a higher degree against the surrounding pubic region than that of females (see ''Results'', and Goymann et al 2004a). This more pronounced eminence of the male cloaca may facilitate contact during copulation.…”

“…Male Black Coucals guard their mates before egg laying. However, once the first egg is laid, males start to incubate and can no longer effectively guard the female (Goymann et al 2004a). As a consequence, ''extra-pair'' fertilisations are quite common with about 37% of nests containing at least one extra-pair young (Muck et al, in press).…”

“…In contrast, males rarely vocalize, do not defend territories, but incubate the eggs and feed the young. Females contribute little or nothing to parental care (Vernon 1971;Goymann et al 2004aGoymann et al , 2005. In Black Coucals, the testicular asymmetry has been reported to be extremely developed, with the left testis being greatly reduced or absent (Ligon 1997), but detailed investigations have so far been lacking.…”

Corticosterone Concentrations Reflect Parental Expenditure in Contrasting Mating Systems of Two Coucal Species

“…These data suggest a substantial difference in time and energy costs of offspring care between male black coucals and pairs of whitebrowed coucals. Female black coucals are very active during the whole breeding season: they frequently sing to attract males and negotiate territorial borders with neighboring or newly arriving females, patrol their territories, and chase after males or competing females (Goymann et al, , 2008Geberzahn et al, 2009Geberzahn et al, , 2010. Further, female black coucals build nests and lay several clutches of typically 4 eggs for their various male partners.…”