Brood age and size influence sex-specific parental provisioning patterns in a sex-role reversed species

Abstract

Parents of altricial young alter provisioning effort based on offspring demand, but life-history differ- ences between the sexes can influence the willingness of each parent to invest in a brood. Previous studies on sex- specific provisioning roles in altricial species suggest a wide range of responses by males and females, which vary depending on the life history of the species. The Northern Flicker (Colaptes auratus) is unusual among altricial birds, as it has partly reversed sex roles with males investing more in parental care than females, it has no-extra-pair young, and it engages in facultative polyandry. We inves- tigated sex-specific provisioning patterns to see what fac- tors (brood size, nestling age, adult age, body condition, nestling sex ratio and partner provisioning level) affected provisioning rates. Additionally, we determined nestling growth rates and estimated nestling energetic demands. Based on 232 filmed provisioning bouts at 82 nests, we found that males provisioned 1.11 times more than females. In addition, provisioning rates by males were primarily associated with nestling age, female provision- ing, brood size, and body condition. Provisioning by females was more strongly related to the male's provi- sioning effort and brood size. Per capita provisioning rates decreased with brood size, resulting in lighter nestlings in large broods. Our results suggest that both parents responded to the changes in brood demands, but do so governed by different factors. We suggest that the rela- tively high provisioning by males is related to high male assurance of paternity.