Environmental predictability and timing of breeding in the San Andrés vireo (Vireo caribaeus)

Predictibilidad ambiental y temporalidad reproductiva en el vireo de San Andrés (Vireo caribaeus)

Abstract

Timing of breeding is a basic trait that should be understood to determine species' requirements during a crucial stage of their life cycle, especially if conservation measures are needed. This is the case of the San Andrés Vireo (Vireo caribaeus), a vulnerable insectivorous bird endemic to San Andrés Island, Colombia. We explored the relative importance of biotic and abiotic cues possibly acting as factors triggering breeding in this species. We hypothesized that being a marked seasonal breeder, the San Andrés Vireo would use biotic and/or abiotic cues, both proximal and ultimate, to predict the optimum time to start breeding. We calculated environmental predictability with Colwell's model using four years of brood patch and cloacal protuberance data, and correlated nest abundance during a single breeding season with biotic (food availability) and abiotic (photoperiod, rainfall) parameters. Environmental predictability was 54% and constancy contributed twice as much as contingency to this value. Photoperiod was the most probable proximate abiotic factor triggering a hormonal state of breeding readiness given its constant, reliable and measurable change in time. The first strong rains after the dry season and insect abundance probably act as ultimate factors contributing to fine tune the timing of breeding on a year-to-year basis. However, because we did not analyze the abundance of fruits, an important component of nestling diet, we might have underestimated the correlation between breeding and food abundance. Future studies should seek to confirm our correlational observations through controlled experiments and explore the importance of fruiting phenology on the timing of breeding.