21,441 research outputs found
More than MOCKing birds: evolution of parental infanticide and siblicide
No full textBook review of More than Kin and Less than Kind: The Evolution of Family Conflict, Douglas W. Mock, Harvard University Press (2004
Inter-island transfers and population dynamics of Seychelles Warblers Acrocephalus sechellensis
No full textIn the 1950s the Seychelles Warbler Acrocephalus sechellensis was a highly threatened single-island endemic species with a population of 26 individuals confined to Cousin Island in the inner Seychelles. Following long-term management of Cousin, the population steadily recovered to around 300–360 birds. In order to give the species the security of additional breeding populations, some warblers were successfully transferred to the islands of Aride and Cousine in September 1988 and June 1990 respectively. During the three years after the transfer to Aride and the first year after the transfer to Cousine, mean territory quality (measured as insect prey available) on these islands was significantly higher than that on Cousin, leading to higher reproductive success per territory and survival of juveniles and adult birds. In November 1991, all transferred birds were still alive, and 205 young had fledged successfully, bringing the total warbler population to c.585 birds. By then there was enough suitable space still remaining on Aride and Cousine for young birds to establish territories and the rise in warbler numbers is expected to continue. The successful establishment of three self-sustaining and viable breeding populations has ensured that the Seychelles Warbler is no longer a globally threatened species.
Facultative sex ratio bias in the offspring of Seychelles warblers
No full textYoung Seychelles warblers (Acrocephalus sechellensis) frequently remain in their natal territories as helpers. Helpers on low-quality territories (as measured by food availability) reduce their parents' future reproductive success, whereas helpers on high-quality territories increase their parents' future reproductive success, thereby improving their own indirect component of inclusive fitness. Helpers are mainly females, which remain longer in their natal territories than males. The Seychelles warbler shows extreme skews in sex ratios of offspring at six months of age, varying from mainly males on low-quality territories to mainly females on high-quality territories. It appears that breeding birds avoid having helpers on low-quality territories and gain helpers on high-quality territories, thereby increasing their reproductive success. There is evidence that the biased sex ratio is caused by biased production, and not because of biased mortality at younger ages: (i) cumulative mortality from the egg stage to the stage at six months of age is insufficient to generate a consistent deviation from sex ratio parity; (ii) all 30 nestlings produced by two pairs on low-quality territories survived to be sexed as sons, and all nestlings produced by two pairs on high-quality territories survived to be sexed as 17 daughters and one son; and (iii) in addition, breeding pairs that were transferred from low- to high-quality territories, switched from the production of male to female nestlings.
Adaptations and maladaptations to island living in the Seychelles Warbler
No full textThe Seychelles Warbler (Acrocephalus sechellensis) was an endangered endemic of the Seychelles islands where, until 1988, the entire population of ca. 320 birds was restricted to the one island of Cousin Island (29 ha). Although warblers can breed independently in their first year, some individuals remain in their natal territory as subordinates, and often help by providing nourishment to non-descendent offspring. The frequency of helping is affected by habitat saturation, variation in territory quality (insect prey availability), and the genetic relatedness between the helper and the offspring. Helping results in indirect benefits from enhancing the reproductive success of close relatives, and direct benefits as improved parental skills and the acquisition of parentage. The overall helping benefits are higher for daughters than for sons, and it is therefore no wonder that most helpers are daughters from previous broods. Furthermore, on low-quality territories breeding pairs raising sons gain higher fitness benefits than by raising daughters, and vice versa on high-quality territories. Female breeders adaptively modify the sex of their single-egg clutches according to territory quality: male eggs on low quality and female eggs on high quality. However, despite the saturated nature of the Cousin population, the possibility of obtaining higher reproductive success on new nearby island, and a well developed flight apparatus, inter-island dispersal by Seychelles Warblers is extremely rare. The Seychelles Warbler is a beautiful example of behavioural and life history adaptations and maladaptations to restricted circumstances.
Experimental evidence for helping and hindering by previous offspring in the cooperative-breeding Seychelles warbler Acrocephalus sechellensis
No full textPrebreeding Seychelles warblers (Acrocephalus sechellensis) frequently act as helpers on their natal territory, aiding in territory defence, predator mobbing, nest-building, incubation (only females) and feeding dependent young of their parents. In some cases helpers could attain breeding status (e.g. by joint-nesting) in their natal group and become co-breeders. Comparisons of group size and reproductive success on a given quality territory suggest that the presence of alloparents (helpers and cobreeders) significantly affects the reproductive success of their parents. The influence of alloparents on reproductive success was examined by removing alloparents from breeding units and comparing the success of natural-sized and artificially reduced groups. Removal experiments, controlled for territory quality, group size and breeder age, showed that the presence of one alloparent significantly improved the reproductive success of its parents. Analysis strongly suggests that this was entirely due to helping behaviour (i.e. providing care to offspring of their parents), thereby improving the helper's inclusive fitness benefits from staying at home. However, these experiments showed also that the presence of two or more alloparents in medium-quality territories significantly decreased reproductive success, compared with groups with one alloparent. Several lines of evidence suggest that this may have been due to the joint-nesting and reproductive competition that could occur in breeding groups, or simply to resource depression when a large number of previous offspring remained on their natal territory.
Mate guarding in the Seychelles warbler is energetically costly and adjusted to paternity risk
No full textMales may increase their fitness through extra-pair copulations (copulations outside the pair bond) that result in extra-pair fertilizations, but also risk lost paternity when they leave their own mate unguarded. The fitness costs of cuckoldry for Seychelles warblers (Acrocephalus sechellensis) are considerable because warblers have a single-egg clutch and, given the short breeding season, no time for a successful replacement clutch. Neighbouring males are the primary threat to a male’s genetic paternity. Males minimize their loss of paternity by guarding their mates to prevent them from having extra-pair copulations during their fertile period. Here, I provide experimental evidence that mate-guarding behaviour is energetically costly and that the expression of this trade-off is adjusted to paternity risk (local male density). Free-living males that were induced to reduce mate guarding spent significantly more time foraging and gained significantly better body condition than control males. The larger the reduction in mate guarding, the more pronounced was the increase in foraging and body condition (accounting for food availability). An experimental increase in paternity risk resulted in an increase in mate-guarding intensity and a decrease in foraging and body condition, and vice versa. This is examined using both cross-sectional and longitudinal data. This study on the Seychelles warbler offers experimental evidence that mate guarding is energetically costly and adjusted to paternity risk.
Conserving the seychelles warbler Acrocephalus sechellensis by translocation from Cousin Island to the islands of Aride and Cousine
No full textThe Seychelles warbler Acrocephalus sechellensis was once a highly threatened single-island endemic species with a population of 26 individuals confined to Cousin Island in the inner Seychelles. Following long-term management of Cousin, the population steadily recovered to around 300-360 birds. Given the vulnerability of one small island in the Indian Ocean, the possibility of establishing the species on additional islands had been proposed as a priority conservation measure, in order to give the species the security of additional breeding populations, lest some ecological disaster should befall the parent population. Successful translocations of warblers to the islands of Aride and Cousine took place in September 1988 and June 1990 respectively. Given the presence now of three healthy breeding populations, it is considered that the Seychelles warbler will soon no longer be a globally threatened species. It is not often that people are allowed to pull a species so dramatically back from the brink of extinction.
The effect of kinship on helping in the cooperative breeding Seychelles warbler (Acrocephalus sechellensis)
No full textIt has previously been argued that the feeding of nestlings by non-parental birds may simply be an unselected consequence of delayed dispersal in cooperative breeding birds in which individuals follow simple rules such as `feed any begging mouth in my natal territory'. However, in the cooperative breeding Seychelles warblers (Acrocephalus sechellensis), helpers are more likely to help feed full siblings (both parents still alive) than half-siblings (one parent died), and do not help at all when the young are unrelated (both parents replaced). Helpers, helping both full siblings and half-siblings reduced their helping effort (food provisioning and period of helping) significantly when rearing young of lesser relatedness. These behaviours suggest that helping has been selected for in the context of promoting an individual's indirect fitness, and that it is not simply a by-product of `provisioning behaviour'. The mechanism by which kin discrimination in helping is achieved appears to be associative learning; birds more often became helpers at nests belonging to related individuals who fed them (as a parent or a helper) when they were nestlings than at nests of related breeders who had not fed them in the nest.
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