Polygynous Groups Research Articles

Singing behavior and singing functions of black‐crested gibbons (Nomascus concolor jingdongensis) at Mt. Wuliang, central Yunnan, China

We used data on loud duetted and solo songs collected from one habituated polygynous group of black-crested gibbons (Nomascus concolor jingdongensis) on Mt. Wuliang, Yunnan, to test several hypotheses about the functions of these songs. The major functions proposed for loud gibbon songs include resource defense, mate defense, pairbonding, group cohesion and mate attraction. Duet bouts are generally initiated by adult males, who select the highest trees near to ridges or on steep slopes as singing trees. Such trees facilitate voice transmission and inter-group communication. Singing trees tended to be located near important food patches and sleeping sites, which supports the resource defense hypothesis. The adult male and two adult females always sang interactively, alternating male phrases with the females' stereotyped great calls, to produce the duets, and females rarely produced great calls if they were more than 30 m from the male. The two females usually produced great calls synchronously during the duet, especially when they were close together. These features support both the mate defense and pairbonding hypotheses. The number of great calls and their degree of synchrony transmit information about spatial relationships and possibly pairbond strength to members to neighboring groups and floating animals. During or after the duet bouts, the adult females and juvenile moved toward to the adult male; and group members maintained a close spatial relationship, which supports the group cohesion hypothesis. Other incidents observed suggest a mate competition role for duets. The adult male always sang when the females started duetting with the subadult male. The subadult male sang solo bouts, but they were not more frequent or longer than bouts initiated by the adult male. Although mate attraction is the likely function of subadult solos, it was not convincingly demonstrated. In conclusion, all hypotheses concerning the function of singing are supported by at least some of the data, and none can be excluded.

Costs and benefits of polygyny in the cichlid Neolamprologus pulcher

Polygyny is regarded as a beneficial strategy for males, whereas females mated with polygynous males (males simultaneously paired to more than one female) often suffer a reduction in pair male contributions. This study examined the costs and benefits associated with polygyny in the cooperatively breeding cichlid Neolamprologus pulcher. In this species, males are facultatively polygynous; some males hold only one territory with one breeding female whereas other males hold multiple territories, each with its own breeding female. Polygynous males were larger than monogamous males and body-scraped less, a behaviour often associated with ectoparasite loads. Polygynous males also had larger testes (controlling for body mass) and higher circulating 11-ketotestosterone levels than monogamous males. Paradoxically, monogamous males occupied higher-quality territories with more shelter and fewer predators. Monogamous males also provided more parental care than polygynous males but the number and survival of young did not vary according to male mating behaviour. The results of our study suggest that females trade-off between male genetic quality and resources in N. pulcher. Our results imply that males holding only one territory may provide their mates with significant assets but may not be able to outcompete neighbours for additional breeding positions because of their small body size and possible higher parasite load. The lack of differences between monogamous and polygynous groups in terms of offspring survival (a measure of reproductive success) suggests that there may be few if any fitness consequences of polygynous pairing for females.

Ecology of Callithrix kuhlii and a Review of Eastern Brazilian Marmosets

We provide data on wild Callithrix kuhlii, a little studied species. We describe their ecology, focusing on demography, diet, and ranging patterns in 8 groups studied from 1995 to 1999. The groups averaged 4.3 individuals, with 1 breeding female and 1–2 adult males, and reproduction was seasonal. Evidence from nonstudy groups indicated the possibility of polygynous group structure. We observed group formation and the transfer of adults between groups. The marmosets ate 20 species of fruit and nectar and 5 exudate species. Home ranges were 34–39 ha, and daily path lengths averaged 1498 m. We include our data in a comprehensive review of eastern Brazilian marmosets to characterize their ecology. Callithrix kuhlii ate more fruit species and less gum species, and had larger home ranges and daily path lengths versus those of most congeners. There was also a tradeoff between travel time and other behaviors. Species with smaller home ranges spent more time foraging and resting and less time traveling than the ones with larger ranges. Attributes consistent with all species included their reliance on gum during fruit scarcity and preference for disturbed habitat. We explored factors relating to the variation in diet and ranging patterns within the eastern Brazilian marmosets, in particular by considering the species in relation to elevation and the extent and proximity of their distribution to the sea. However, large intraspecific variation resulting in part from variable levels of anthropogenic disturbance across sites confounded our ability to verify trends corresponding to the geographic characteristics.

Variation in the mating system of oribi and its ecological determinants

AbstractFlexibility (varying from monogamy in South Africa to polygyny in East Africa) has been documented in the mating system of the oribi (Ourebia ourebi) by several authors. To investigate this, a population was studied in Northern KwaZulu‐Natal (South Africa). The adult sex ratio was one male to 1.38 females and the mean group size was 2.1 (n = 13). Although monogamous and polygynous groups occurred in the study population, the polygynous groups were unstable and depended on seasonal food abundance. Comparison of oribi populations across Africa suggests that variation in the mating system is determined mainly by predation risk and altitude (most likely through its effect on graze quality). In areas of high predation risk, oribi can survive only when resource quality permits females to forage in groups, thereby allowing males to be polygynous.

Emerging infectious diseases and animal social systems

Emerging infectious diseases threaten a wide diversity of animals, and important questions remain concerning disease emergence in socially structured populations. We developed a spatially explicit simulation model to investigate whether—and under what conditions—disease-related mortality can impact rates of pathogen spread in populations of polygynous groups. Specifically, we investigated whether pathogen-mediated dispersal (PMD) can occur when females disperse after the resident male dies from disease, thus carrying infections to new groups. We also examined the effects of incubation period and virulence, host mortality and rates of background dispersal, and we used the model to investigate the spread of the virus responsible for Ebola hemorrhagic fever, which currently is devastating African ape populations. Output was analyzed using regression trees, which enable exploration of hierarchical and non-linear relationships. Analyses revealed that the incidence of disease in single-male (polygynous) groups was significantly greater for those groups containing an average of more than six females, while the total number of infected hosts in the population was most sensitive to the number of females per group. Thus, as expected, PMD occurs in polygynous groups and its effects increase as harem size (the number of females) increases. Simulation output further indicated that population-level effects of Ebola are likely to differ among multi-male–multi-female chimpanzees and polygynous gorillas, with larger overall numbers of chimpanzees infected, but more gorilla groups becoming infected due to increased dispersal when the resident male dies. Collectively, our results highlight the importance of social system on the spread of disease in wild mammals.

Behavioral strategies and hormonal profiles of dominant and subordinate common marmoset (Callithrix jacchus) females in wild monogamous groups

New insights into the mating systems of common marmosets suggest that they are mainly monogamous, although polygyny and polyandry occasionally occur. Long-term monitoring of wild common marmosets has shown that some reports of polygynous groups (i.e., groups that contain more than one reproducing female) in fact indicate an unbalanced reproductive output associated with extragroup copulation. In this study we describe the behavioral and hormonal profiles of common marmoset (Callithrix jacchus) females living in three wild monogamous groups (Q, PBf, and T), varying from five to 11 individuals, at Nísia Floresta field station, RN, Brazil. The mating system of the groups was previously characterized in terms of affiliative, sexual, and mate-guarding behaviors. Behavioral data were collected once a week, and fecal samples were collected at least twice a week for 10-16 months, depending on the group. A preferential allogrooming relationship was recorded between dominant males and females. Under field conditions the reproductive inhibition of subordinate females appears to be more behavioral than hormonal, since subordinate females of the three groups ovulated and two conceived during the study. In these cases, the subordinate and dominant females reproduced 1 month apart, and infanticide (one case confirmed and one suspected) appeared to be part of the reproductive strategy of dominant females. Following the infanticide, ovarian inhibition (group T) or emigration and return to the natal group (group PBf) were observed. In the third group (Q) the subordinate female showed hormonal profiles compatible with pregnancy, but no infants were seen. These findings reflect the different alternatives that wild subordinate common marmoset females use to reproduce.

Variation in mating system and group structure in two populations of swift foxes, Vulpes velox

We studied 26 reproductive groups of swift foxes, Vulpes velox, from both high- and low-density areas during three field seasons in northwestern Texas, U.S.A., to examine whether differences in population density affect mating system and group structure. Although high- and low-density populations were only separated by 40 km and vegetation and diets were similar between sites, polygynous groups, communal denning and nonbreeding females occurred in the area of high density, whereas only monogamous pairs occurred in the area of low density. Annual survival of adult swift foxes was 66% in the area of high density, but 44% in the area of low density. Predation from coyotes, Canis latrans, was the only mortality factor that differed ( P=0.01) between sites and contributed most to differences in survival. Although previous research indicated that variation in social systems among canids is related to bottom–up forces (i.e. food, habitat), the results of our study indicate that variation in social systems can also be related to top–down forces (i.e. predation, displacement by larger competitor).

Second to fourth digit ratio, sexual selection, and skin colour

Skin pigment may be related to mate choice, marriage systems, resistance to microorganisms, and photoprotection. Here we use second to fourth digit ratio (2D:4D) to disentangle the relationships among these variables. There is evidence that 2D:4D is negatively associated with prenatal testosterone and positively with prenatal oestrogen. We show (i) a negative association between skin colour and 2D:4D in Caucasian women, but not in men, suggesting that skin colour in women is partly dependent on prenatal oestrogen; and (ii) Caucasian subjects with low 2D:4D reported higher susceptibility to sun-burn, athlete's foot and eczema than subjects with high 2D:4D, suggesting that prenatal testosterone increases susceptibility to sunburn and skin diseases. Frost [ Hum. Evol. 9 (1994) 141] has reported that with latitude controlled, highly polygynous peoples have relatively dark and monogamous peoples relatively light skin. We suggest that polygynous populations incur selection for high prenatal testosterone and low prenatal oestrogen because of competition among men for wives. Such groups have low 2D:4D, and high susceptibility to sunburn and skin infections which may result from the immunosuppressive effects of prenatal testosterone. Where polygynous groups are found at low latitudes, they have evolved dark skin for protection against UV and microorganisms. More monogamous peoples experience selection for low prenatal testosterone and high prenatal oestrogen as a result of mate choice for light-skinned oestrogenised women. Such groups have high 2D:4D, resistance to sunburn and skin infections, and light skin. The association between very dark skin and low latitude exists only when polygynous societies are found at low latitudes, as is common in sub-Saharan Africa, but not in the New World.

Variability in adult group compositions of a prosimian primate

Many species fall into specific mating-system categories, and that category is usually associated with a suite of behavioral and morphological characteristics. Several lemur species, including Propithecus diadema edwardsi, have been labeled "idiosyncratic" because variation in socionomic sex ratios among groups is consistent with wide variation in social structure. We used several hypotheses founded in behavioral ecology to assess variability in P. d. edwardsi. First we examined 46 group-mating seasons to quantify variability. We then tested predictions that the number of males per group would increase as the number of adult females increased, and the number of males would increase as female mating synchrony increased. Examining variation in offspring survival relative to the number of adult males in a group may tell us which composition is likely to persist into the future, so we also hypothesized that as the number of males in a group increased, fertility and offspring survival would increase. We found an equal distribution of polygynous, polygynandrous, pairs, and polyandrous groups. Furthermore, female distribution and mating synchrony did not predict the number of males, and offspring survival was not correlated with the number of males. Since infants survived equally well in groups of all compositions, sifakas experienced no pressure to maintain a particular number of adult males per adult female. The small number of adults per group (mean=3.2) may result from balancing feeding competition against predator detection. Augmenting the mate pool available from the group with mates from neighboring groups may promote the notable variability seen in the adult group compositions of sifakas.

Mating system and kin relationship between adults and young in the shell-brooding cichlid fish Neolamprologus meeli in Lake Tanganyika

Mating system and parental behavior of ten monogamous pairs and two polygynous groups of the Tanganyikan cichlid Neolamprologus meeli were observed in their natural habitat. The home ranges of males and females overlapped with each other. Most groups included one to six young. Paternal and maternal relationships were determined for 22 young from DNA microsatellite markers. Three types of kinship were found: (I) kinship to both the male and female; (II) kinship to females only; and (III) non-kinship to both sexes. In the groups with type II young, step-fathering or sneaking may have occurred. Type III young were larger than type I, suggesting that the former were of sufficient size to leave their birth nest and settle in the territories of foster parents. Both males and females drove out potential predators of young (including three species of Lepidiolamprologus) as a parental behavior. Adults with type III young attacked approaching predators with as much frequency as those with type I young only, indicating that they provided alloparental care. Adults and young swam together, but, a significant difference existed in the frequencies of interactions between adults versus kin young and adults versus non-kin young. The results suggest that both adults and young recognized kin.

Reversed Sex‐Change in the Protogynous Reef Fish Labroides dimidiatus

Protogynous hermaphroditism, or female‐to‐male sex change, is known for many reef fishes including wrasses (family Labridae) in which large males monopolize mating. When the dominant male disappears from a polygynous group, the largest female may change sex within a few weeks. Such social control of sex change was first documented in harems of the cleaner wrasse Labroides dimidiatus almost 30 yr ago. To examine whether change of social status would induce males of L. dimidiatus to perform reversed sex‐change, we conducted experiments: (i) releasing single males near lone males whose mates have been removed in the field; and (ii) keeping two males in a tank. Smaller males changed back to females when they became subordinate: it took 53–77 d (n=3) for them to complete gonadal sex change and release eggs in the aquarium. The male–male pairs performed spawning behavior, with the smaller male in the female role already 5–58 d before completion of gonadal sex change. This is the first report of reversed sex‐change among protogynous wrasses. Moreover, we conducted another experiment, keeping a pair of a male and a larger female in a tank (n=1). We found sex change by both mates, which has not been reported from any fishes. Thus, the sex of L. dimidiatus is strictly determined by social status whenever it changes after mate loss.

TRIOS OF BROWN SKUAS AT BIRD ISLAND, SOUTH GEORGIA: INCIDENCE AND COMPOSITION

Abstract Cooperative breeding is unusual in seabirds, but recorded in varying proportions in Brown Skuas (Stercorarius [= Catharacta] lonnbergi). With no evidence for kin selection or delayed dispersal, nor for any reproductive advantage, the reason for its occurrence in skuas is uncertain. This study describes the incidence, composition, and breeding characteristics of trios of Brown Skuas at Bird Island, South Georgia. Trios were recorded in nine seasons, including a polygynous and a polyandrous trio found in both 2000–2001 and 2001–2002. In some years, birds hatched three chicks from supranormal clutches, which is exceptional in skuas and jaegers, yet their overall performance was no better than monogamous pairs. I suggest that compared with closely related taxa, Brown Skuas have a slight behavioral or genetic predisposition that facilitates cooperative breeding. Cooperation conveys a minor advantage in territory acquisition, but none in terms of reproductive success (particularly for polygynous groups...

Mate guarding and social mating system in male common chameleons (Chamaeleo chamaeleon)

AbstractMale common chameleons Chamaeleo chamaeleon actively followed the female closely as a typical mate guarding behaviour during the mating season. Guarding behaviour and spatial organization were studied in 34 radio‐tagged males in a population in southern Spain during three summers. Timing and extent of guarding were highly variable among males. Overall, guarding started on 16 August (range 28 July–5 September, n=34) and ended on 4 September (range 21 August–15 September, n=24) lasting 13.4 days (range 0–46 days, n=30). Males showed a polygynous serial‐type mating system where males sequentially guarded (and mated) several females during the breeding season but only one at a time. The number of guarded females (mean 2.8, range 0–8, n=34) and number of mates per male (mean 0.7, range 0–3, n=34) were also highly variable among males. In general, guarding males abandoned the females soon after mating in association with clear signs that females were no longer receptive. Males showed a remarkably complex spatial organization in close association with the home range of guarded females. Guarding behaviour resulted in territorial behaviour, and ‘stable’ as well as ‘mobile’ territories were recorded. In ‘stable’ territories, males defended non‐overlapping areas where the home range of one female or more was included. Although monogamy was the predominant mating system recorded in this population, social polygyny occurred in all study years. Polygynous groups were only feasible because females aggregated in small‐sized areas without apparent symptoms of intrasexual competition. Breeding asynchrony of females seems to influence this complex mating system as more competitive (large) males mated with large (early reproducing) females and small (late reproducing) ones (cf. Cuadrado, 1999). Most aggressive interactions were male–male chasing of a solitary intruder by a guarding male. A removal experiment of guarding males revealed that newcomers were small‐sized males, suggesting that an important fraction of males were acting as floaters searching for mating opportunities. Male characteristics (especially size and body weight) were the main factors influencing the spatial organization and the reproductive success of males in this population.

Sexual conflict over mating system: the case of a pair-territorial filefish without parental care

We studied the optimal mating system from the male's and female's point of view in the longnose filefish, Oxymonacanthus longirostris, which is predominantly monogamous but can also be polygynous, and lacks parental care. This fish typically moves about in closely coordinated heterosexual pairs, which share a feeding territory throughout the year. We conducted two types of male removal experiment involving manipulation of male and female mating status to examine whether the fitness consequences for each sex are influenced by mating status, and we estimated the fitness components for naturally monogamous and polygynous individuals. Polygyny was advantageous to males because of higher reproductive success, but monogamy was advantageous to females because they produced fewer eggs when their mates mated polygynously. This was due to polygynous males spending less time on territorial defence with their mates than monogamous males, resulting in a decrease in female feeding frequency. Thus, there was a sexual difference in the optimal mating system. The cost of polygyny to females led to intense female–female competition over the male in a polygynous group. However, two factors, a slightly female-biased sex ratio in the population and interference by males in the aggression between females, made it difficult for some females to form the optimal mating system. Females in a polygynous group, therefore, make the best of a bad situation. Thus, the resulting mating system of O.longirostris seems to be an outcome of sexual conflict over the mating system: males gain from polygyny, whereas monogamy increases female fitness.

Reproductive division of labour without dominance interactions in the queenless ponerine ant Pachycondyla (=Ophthalmopone) berthoudi

In the queenless ponerine ant Pachycondyla (=Ophthalmopone) berthoudi, a variable proportion of the workers in each colony are mated and lay diploid eggs ("gamergates"). Virgin workers do not reproduce. The mechanism of reproductive regulation was investigated by splitting colonies to create groups of workers containing one, several or no gamergates. In the monogynous groups, no aggressive interactions were observed and virgin workers showed no signs of ovarian development. In polygynous groups, aggressive interactions were also not observed and the gamergates rarely interacted with each other; again, virgin workers showed no signs of ovary development. The groups without gamergates consisted of a large proportion of callows, with a variable number having developed ovaries in each. No aggressive interactions were observed, and there was no correlation between inter-individual behaviours and reproductive status. Although the eggs produced in these virgin groups were embryonated, none hatched. When sterile workers were separated from gamergates by a double mesh screen, several developed their ovaries and laid eggs. However, when separated by a single mesh antennate screen and allowed to gamergates, virgin workers remained infertile. Our results suggest that chemical signals produced by reproductive individuals are important in reproductive regulation in this species. The absence of any form of behavioural interactions in the regulation of reproduction is unusual for a queenless ant.

Parental care in a polygynous group of bat-eared foxes, Otocyon megalotis (Carnivora: Canidae)

This study reports the first recorded instance of polygyny and communal nursing in Otocyon m. megalotis. The polygynous group, which was studied in the Kalahari Desert, consisted of a male, two lactating females and a litter of five pups. New aspects of parental care that were observed include the bringing of food items to pups at the den. Although bat-eared foxes in this area seldom capture lizards for their own consumption, lizards were the main food item carried to the den. It is suggested that bat-eared foxes specifically seek out lizards because they are more easily transportable than their normal insect prey. Despite this behavioural adaptation, there is relatively little opportunity for the male to contribute to the nutrition of the pups when compared to the contribution made by the males of large carnivorous canids, which routinely bring large volumes of meat to the den. Instead, young bat-eared foxes depend heavily on milk, so the females have to forage for extended periods to replenish their milk supplies. This study shows that the major duties of males are guarding and grooming the pups while the females are foraging. In this social context there are relatively few disadvantages in sharing a father between two litters and these disadvantages are occasionally outweighed by the benefits of communal care, amongst which are cooperative attacks on predators and alternate nursing.

Women of principle: female networking in contemporary Mormon polygyny

This book offers an in-depth study of the female experience in one Mormon polygynous community, the Apostolic United Brethren. Women in such rigid, patriarchal religious groups are commonly portrayed as the oppressed, powerless victims of male domination. Janet Bennion show, however, that the reality is far more complex. Many women converts are attracted to this group, and they are much more likely than male converts to remain there. Often these women are seeking improved socio-economic status for themselves and their children, as well as an escape from their marginalized status in the mainstream Mormon church. In the polygynous group women experience rapid assimilation, autonomy, and upward mobility. Bennion supports her study with narratives from the lives of women now living in the group-narratives that clearly reveal why many mainstream Mormon women are viewing polygyny as a viable alternative to the difficulties to single-motherhood, spinsterhood, poverty, and emotional deprivation.

Territoriality and monogamous pairs in a solitary ungulate, the Japanese serow, Capricornis crispus

The social organization of Japanese serows was studied in a 320-ha forest for 7 years. Serows were usually solitary (79% of sightings), but temporally formed groups of two to four animals (mostly mother–kid units, or male–female pairs with or without a kid). Home ranges of adult males and adult females (10–15 ha) were stable, and most parts of the ranges were defended as territories against other individuals of the same sex throughout the year. Several adult males were non-territorial residents. The main mating unit consisted of a monogamous pair of which the male's range almost completely overlapped the female's. About 20% of territorial males were polygynous each year, their ranges overlapping the ranges of two females; they could produce nearly twice as many offspring as monogamous males. Mating units were usually maintained for several years, although polygynous groups were not as stable as monogamous pairs. Female territories, which function to defend food resources, were dispersed and seemed to restrict the number of mates available to territorial males. This is why the serow formed predominantly monogamous pairs, although the male's strategy is polygyny.

Molecular Genetic (RAPD) Analysis of Breeding Magpie Geese

-Magpie Geese (Anseranus semipalmata) typically form nesting trios consisting of two females and one male, an uncommon breeding arrangement for waterfowl. To study aspects of their reproductive biology, 20 reproductively active adults representing seven reproductive groupings (broods) were scored for 106 polymorphic primer-specific RAPD bands. Genetic distances between all possible adult pairs were calculated, and these values were analyzed using the Mantel test. In the pairwise comparison of genetic distances, those between males were significantly less than those for other adult combinations (P < 0.05). Using the same analytical approach, we found that females that shared a nest were more like one another than were females that did not share a nest (P < 0.05). We suggest that a plausible hypothesis to account for the relative genetic homogeneity of the male population is that males seeking to enter the breeding population do so at their natal site. The females they recruit are more closely related to one another than are females in general. Received 5 April 1995, accepted 29 June 1995. LARGE NUMBERS of Magpie Geese (Anseranus semipalmata) congregate at seasonal wetlands in tropical northern Australia. The bird's unique morphology (including partially webbed, heavily clawed feet with an opposable fourth toe) led to its taxonomic placement in its own family. This uniqueness also is evident at the molecular level, and recent taxonomies derived from mitochondrial DNA sequences support the view that this species should be assigned to a family of its own (Sraml et al. 1996). Although abundant in parts of northern Australia, the current distribution of the Magpie Goose is only a remnant of its former range, which has been severely restricted over the past 200 years by the introduction of European-style agricultural practices. Situations that threaten this species could arise again as the result of conflicts between the bird's habitat requirements and changing human activities. Proposed changes associated with tropical agriculture could threaten the conservation status of these birds (Whitehead 1991). In attempting to sustain adequate numbers of a species, it is important to understand the species' reproductive biology. Unlike most water4E-mail: horn@science.canberra.edu.au fowl, Magpie Geese commonly form breeding trios consisting of two females and one male (Frith and Davies 1961). In situations where females share a nest, all three attendants typically have a direct reproductive (genetic) interest in the clutch, and they are involved in many aspects of care and defense of the eggs and young. Chicks remain with their parents for their first year of life, possibly learning about seasonal resource distribution (Whitehead and Tschirner 1990). The stability of these polygynous groups from year to year distinguishes Magpie Geese from other communal breeders (Brown 1987). When joined in a reproductive trio, individual females seem to decrease their potential reproductive output as measured by numbers of eggs laid. Egg counts (x = 8.6) in nests with only one female and one male are not much smaller than those (x = 9.4) from nests with two females and one male (Frith and Davies 1961). In addition, behavioral observations of trios suggest that males mate with both females and that both females contribute eggs approximately equally to these joint nests. Assignments of young to specific females have been done using restriction-fragment-length-polymorphism (RFLP) analysis of DNA. In making those assignments, conspecific nest parasitism was

Molecular sexing of the communally breeding pukeko: an important ecological tool.

A central biological parameter in the study of any animal population is the accurate assignment of sex. Indeed any ecological study of a population requires information on sex composition in relation to such biological factors as behaviour, movement, mortality and birth rate. However, our ability to assign the sex of adults of many avian species is poor and the sexing of young is universally difficult. We report here the successful application of a molecular technique for the assignment of sex in the communally breeding pukeko or purple swamphen (Porphyrio porphyrio melanotus). W- and Z-linked chromosome fragments in digested genomic DNA of pukeko were detected with the DNA probe pMg1. We consequently show that this species breeds in polyandrous, polygynous and polygynandrous groups. Finally we discuss why recent molecular methods represent important new tools in ecology.