John L. Craig

Incestuous mating in a communal bird: a family affair

In the past, observations of animal dispersal has been taken as evidence of inbreeding avoidance. Reduced dispersal by the young of communal breeders makes them ideal for investigating the possibility of inbreeding and/or inbreeding avoidance. Communally breeding pukeko are especially suitable for such a study because they exhibit extreme philopatry, have a polygynandrous mating system, and engage in readily observed copulations. Results from a 7-yr study show that most pukeko remain and breed in their natal territory and incestuous matings are common. In contrast, incidents of dispersal out of the natal territory were infrequent, involving only males. Outbreeding appeared less common than inbreeding. Dispersal by breeding males that had mated previously with their offspring could not be logically linked to incest avoidance, but movements of nonbreeding subadults might have been related to either incest avoidance or intersexual dominance. Except for young nonbreeding males that tend to be subordinate to breeding females, male pukeko dominate females. A few subadult males that were stopped from copulating by the aggressive behavior of their mothers subsequently dispersed, whereas others showed reduced sexual behavior in the presence of their mothers. Both incest avoidance by the mothers (but not the sons) and parental dominance could explain these observations. Parental dominance seems to be a viable explanation because there were no examples of daughters avoiding matings with their fathers or sisters avoiding matings with brothers. Results from other studies of communally breeding birds also show various degrees of incestuous mating. Data from one in-depth study on acorn woodpeckers, from which incest-avoidance mechanisms have been postulated, is considered in detail; the results appear equivocal and do not exclude alternative explanations. Additional factors, such as a level of fecundity markedly higher than that of survival and a long history of communal (and presumably incestuous) habits in pukeko, lead us to question whether inbreeding among pukeko is likely to have deleterious genetic effects. The possibility of nonrandom fusion of gametes would also support this view. Overall, pukeko appear to demonstrate higher levels of incestuous matings than current research and theories on the evolution of vertebrate mating systems would have predicted. We argue that this conflict arises as a product of the unquestioning assumption by many workers that behavior leading to inbreeding has been selected against or that inbreeding-avoidance mechanisms have been selected for in animal populations.

Pair and group breeding behaviour of a communal gallinule, the pukeko, Porphyrio P. Melanotus

Abstract Pukeko, Porphyrio porphyrio melanotus breed as pairs or groups and the breeding behaviour of individuals in all units is described and compared. Courtship, including copulation, occurred between all adult members in a territory although male-female copulations were most frequent. Low ranking yearlings were excluded from copulation. Participation in copulation by more than two birds was common, and, along with homosexual behaviour, is believed to help synchronize sexual cycles allowing several females to lay in the same nest at the same time. Only adults incubated, while all birds in a territory assisted with chick care, the degree of participation varying with status. In pair territories, older chicks helped feed younger chicks. Stable kin groups were more coordinated and showed less competitive aggression among members than non-kin groups of unstable membership. The significance of these results is discussed and it is argued that in a situation where an adult group is necessary for the defence of a breeding territory, then it is in the interests of all these individuals to participate in all breeding activities.

The foraging of New Zealand honeyeaters

Abstract New Zealand has three species of honeyeaters, all of which feed on nectar, fruit, and ‘insects’. There is disagreement between published data and those becoming available from long-term studies on the relative proportion of these items in the diet. The effect of factors such as body size, dominance status, degree of movement, and time of year on diet and foraging behaviour are outlined, and predictions of differences between species and between sexes are made. A brief comparison of foraging in relation to the flora is made between New Zealand and Australian species.

Social dominance in communal Mexican jays Aphelocoma ultramarina

Abstract Social dominance among members of seven social units of communal Mexican jays ( Aphelocoma ultramarina ) was studied at feeding stations during the non-breeding season. Hierarchies were generally linear. Males were usually dominant to females and there was a tendency for the oldest male in each unit to be the most dominant adult. An unusual pattern of high social status of yearlings was observed. We attribute the high social status of yearlings and adult males to different causes. Adult male dominance is probably related to competition for breeding opportunities within each social unit. We tentatively interpret the dominance of the yearlings in terms of payoff asymmetries and parental facilitation.

The evolution of complexity in broadcast song of passerines

Abstract An overall theory for the evolution of complexity in passerine broadcast song is advanced based on the proposition that new birds should attempt to match the songs of residents. We assume that social systems result from competition between individuals for resources. Individuals which by aggressive interaction have attained some priority of access to a resource (territory, food, or mate) should advertise this. New birds singing in an area will reveal their non-residential status by their song and hence will announce an assymmetry in competition that favours the residents because of their prior knowledge. Thus new birds should learn to match in order to reduce this asymmetry. Counter-selection on residents to reduce the incidence of matching should favour the evolution of song complexity. The degree of complexity should vary directly with the degree of competition. Predictions from these assumptions are advanced.

Effects of familiarity on the outcome of translocations, I. A test using saddlebacks Philesturnus carunculatus rufusater

Translocation, the intentional release of a species in a new location, plays an important role in the conservation of endangered species. Consequently, there is a critical need for research on factors affecting the outcome of translocation attempts. This study addresses the hypothesis that founder groups will do better if they are made up of individuals that are familiar with one another. The hypothesis is based on research on birds showing that familiarity between mates and neighbours leads to lower aggression and higher reproductive success. Our test involved a translocation of the North Island saddleback Philesturnus carunculatus rufusater, a New Zealand forest bird restricted to islands free of mammalian predators. We created two founder groups of 18 birds each, one made up of birds from a single small forest patch, and including five known pairs, and the other a mixture of birds from several patches, with no pairs. We released the groups in different parts of an island, and assessed the effects of familiarity on survival, dispersal, pair bonding, and reproduction. The two groups showed similarly high survival, and both dispersed widely. Pair bonds formed more quickly among the familiar birds, even though only one of the five original pairs stayed together after translocation. While pairing among unfamiliar birds tended to be delayed, they achieved a similarly high rate of pairing by the start of the breeding season, and reproductive output was similar for familiar and unfamiliar pairs. We therefore found no evidence that using familiar individuals would improve the outcome of bird translocations. We note that familiarity could be more important with other species and/or in other circumstances. However, we also note the potential costs of using familiar individuals.

The population ecology of Rattus exulans on Tiritiri Matangi Island, and a model of comparative population dynamics in New Zealand

Abstract On Tiritiri, a small predator-free island in northern New Zealand, kiore (Rattus exulans) were live and snap trapped in grassland and forest. In both habitats, kiore abundance peaked in late summer/autumn. The increase followed a 3 month breeding season during which females produced two to three litters, each averaging 7 young. During the population decline in autumn and winter, animals lost weight. Few bred in the breeding season of their birth and none lived to breed in a second breeding season, so the population consisted of distinct age cohorts. These patterns may relate to a highly seasonal food supply. Kiore elsewhere in New Zealand show seasonal breeding, but the length of breeding, sexual maturation, and litter size vary. Other studies of kiore in the Pacific show less marked seasonal fluctuations, longer breeding seasons, and smaller litters. We propose a model to explain the variation in rodent demography in New Zealand. The model is based on the seasonal availability of food, along wit...

Resource distribution, aggressive asymmetries and variable access to resources in the nectar feeding bellbird

SummaryA continuum concept of spatial organization linking territoriality and social hierarchy suggests that individuals will alter their degree of exclusiveness and priority of access to resources in accord with the net benefits of aggression. Thus changes in resource distribution will produce changes in the control of resource space for any one individual. Similarly when comparing among individuals, responses will change in accord with their aggressive abilities when compared to those of possible opponents. The existence of such a continuum model of spacing was investigated in a nectar feeder, the New Zealand bellbird (Anthornis melanura: Meliphagidae). A natural change in spatial distribution of resources from highly concentrated to dispersed provided an opportunity to follow changes in access for known individuals. Comparison of individuals of different hierarchical status, sex and residential status was also possible within each system as was an estimate of comparative rewards. At the concentrated resource, individuals could be ranked in a dominance hierarchy although spatial separation between more dominant individuals did occur. At the more spatially dispersed resource, most individuals obtained a level of exclusive use. Access to both resources varied for different individuals but the asymmetries that related to greater access in one system also produced greater access in the other resource.

Are communal pukeko caught in the prisoner's dilemma?

SummaryThe prisoners dilemma of game theory provides a possible explanation for communal breeding in the pukeko (Porphyrio porphyrio, Aves) where group breeding birds are at a reproductive disavantag compared to pairs. Territorial defence is largely the realm of males. A male who ‘defect’ on neighbours by taking in an extra male defender and so becoming communal stands to gain territorial area and possibly higher reproductive success. Neighbours are forced to follow suit if additional males are available or lose their territory and therefore their breeding opportunities. If neighbours also admit an extra defender, the initial ‘defector’ loses his advantages and all males end up with the lower breeding success of communal groups. Such ‘defection’ to a communal habit appears to be the only stable solution.

The relationship between presumed gamete contribution and parental investment in a communally breeding bird

SummaryMeasures of relative gamete contribution were related to degree of parental investment for both males and females from six groups of communally breeding pukeko (Porphyrio porphyrio). If there is a fitness cost to participation in parental duties, then for males parental investment should relate to degree of confidence of paternity while for females investment should relate to the number of eggs laid. Data were analysed in two ways: (1) by looking at individuals of the same sex within the same group to see if males that had a greater probability of paternity and females that had greater number of eggs in a nest subsequently invested relatively more in parental duties and (2) by pooling the data from the six groups and determining if there was a positive correlation between measures of presumed gamete contribution and amount of parental investment. The results from both types of analyses are variable and give no clear support for a positive relationship between presumed gamete contribution and parental investment even though a possible fitness cost is suggested. Factors which might influence investment are discussed.