Seasonality and trade-offs in equatorial rufous-collared sparrows (Zonotrichia capensis)

Abstract

The majority of vertebrates are tropical, existing in an environment with low temperature seasonality. However, there is a strong research bias towards temperate-zone studies of seasonality. I investigated the timing of life history stages and trade-offs in tropical rufous-collared sparrows (Zonotrichia capensis) in the humid Andes of Ecuador, then compared my data to temperate-zone Zonotrichia. In Chapter II, I investigated the function of male territorial aggression. Males had peak territorial aggression scores during pre-breeding and nesting, suggesting that paternity protection and food resource defense are the primary selective forces shaping male territorial behavior. Territorial aggression responses depended on the life history stage of males, which were not synchronized within the general population. In Chapter III, I tested for a trade-off between male territorial aggression scores and paternal provisioning rate. Males with higher provisioning rates had nestlings with larger body size, but contrary to the findings of previous studies, there was no direct relationship between aggression and paternal provisioning. In Chapter IV, I investigated how Z. capensis allocated supplemental food. Previous studies (mainly in temperate-zone breeding birds) found food supplements were allocated to reproduction. We supplemented fed birds in both non-breeding and feeding fledglings life history stages; both groups molted (replaced feathers) in response to supplementation, thus invested in their own maintenance over immediate reproduction. In Chapter V, I tested whether latitude and/or altitude are good predictors of reproductive synchrony in Zonotrichia. Reproductive synchrony indices overlapped among tropical and temperate populations. The high altitude, temperate-zone Zonotrichia population had the highest synchrony index, but there was only a weak relationship of altitude in a comparison of tropical populations. Cumulatively I found that tropical humid-forest resident Z. capensis time life history stages according to individual condition and history and not by overarching climatic cues.