Experimentally induced antipredator responses are mediated by social and environmental factors
Groenewoud, Frank ; Kingma, Sjouke A. ; Bebbington, Kat ; Richardson, David S. ; Komdeur, Jan - \ 2019
Behavioral Ecology 30 (2019)4. - ISSN 1045-2249 - p. 986 - 992.
Antipredator defense - Nest defense - Nest predation - Parental investment - Seychelles warbler - Trade-off
Nest predation is a common cause of reproductive failure for many bird species, and various antipredator defense behaviors have evolved to reduce the risk of nest predation. However, trade-offs between current reproductive duties and future reproduction often limit the parent’s ability to respond to nest predation risk. Individual responses to experimentally increased nest predation risk can give insights into these trade-offs. Here, we investigate whether social and ecological factors affect individual responses to predation risk by experimentally manipulating the risk of nest predation using taxidermic mounts in the cooperative breeding Seychelles warbler (Acrocephalus sechellensis). Our results show that dominant females, but not males, alarm called more often when they confront a nest predator model alone than when they do so with a partner, and that individuals that confront a predator together attacked more than those that did so alone. Dominant males increased their antipredator defense by spending more time nest guarding after a presentation with a nest predator, compared with a nonpredator control, but no such effect was found for females, who did not increase the time spent incubating. In contrast to incubation by females, nest guarding responses by dominant males depended on the presence of other group members and food availability. These results suggest that while female investment in incubation is always high and not dependent on social and ecological conditions, males have a lower initial investment, which allows them to respond to sudden changes in nest predation risk.
Compensatory and additive helper effects in the cooperatively breeding Seychelles warbler (Acrocephalus sechellensis)
Boheemen, Lotte A. van; Hammers, Martijn ; Kingma, Sjouke A. ; Richardson, David S. ; Burke, Terry ; Komdeur, Jan ; Dugdale, Hannah L. - \ 2019
Ecology and Evolution 9 (2019)5. - ISSN 2045-7758 - p. 2986 - 2995.
additive care - compensatory care - cooperative breeding - investment strategies - load-lightening - parental care - Seychelles warbler
In cooperatively breeding species, care provided by helpers may affect the dominant breeders’ investment trade-offs between current and future reproduction. By negatively compensating for such additional care, breeders can reduce costs of reproduction and improve their own chances of survival. Alternatively, helper care can be additive to that of dominants, increasing the fledging fitness of the current brood. However, the influence helpers have on brood care may be affected by group size and territory quality. Therefore, the impact of helping needs to be disentangled from other factors determining offspring investment before conclusive inferences about the effect of help on additive and compensatory care can be made. We used 20 years of provisioning data to investigate the effect of helping on provisioning rates in the facultative cooperatively breeding Seychelles warbler Acrocephalus sechellensis. Our extensive dataset allowed us to statistically disentangle the effects of helper presence, living in larger groups and different food availability. We show compensatory and additive care (i.e., partial compensation) in response to helper provisioning. Helpers lightened the provisioning load of the dominant male and female and increased total provisioning to nestlings. This was irrespective of group size or territory quality (food availability). Moreover, our results illustrate sex-specific variation in parental care over the course of the breeding event. We discriminate between temporal variation, group size, and territory quality processes affecting cooperative care and as such, gain further insight into the importance of these factors to the evolutionary maintenance of helping behavior.