Demographic and behavioral responses of breeding birds to variation in food nest predation and habitat structure across multiple spatial scales

Avian incubation attentiveness has important fitness consequences through its influence on the number and quality of hatched young and energetic costs imposed on parents. Nest attentiveness is highly variable across species and geographic regions. We reviewed the literature and show a worldwide pattern that nest attentiveness is generally lower in southern compared with northem-latitude passerine species. We then experimentally tested the hypothesis that greater food limitation may be responsible for low nest attentiveness in southern birds. We used the karoo prinia {Prinia maculosa) in South Africa, which has very low nest attentiveness (~ 50%) compared with average (~ 73%) north-temperate species. We provided supplemental food during early incubation to experimental females and measured nest attentiveness and on-and off-bout lengths compared to paired control females. Nest attentiveness was significantly increased at food-provisioned nests (57% versus 49%). Food-supplemented females spent significantly less time off the nest than control females, whereas mean on-bout lengths did not differ. However, mean nest attentiveness of food-provisioned females was still substantially below attentiveness of other similar bird species worldwide. We suggest that food can be an important proximate influence on parental care behavior within species, but the low attentiveness of many southern bird species appears to represent an evolved trait that is not simply constrained by food.