Offspring growth and mobility in response to variation in parental care: a comparison between populations

Life history theory emphasizes the importance of trade-offs in how time and energy are allocated to the competing demands of growth, fecundity, and survival. However, avian studies have historically emphasized the importance of resource acquisition over resource allocation to explain geographic variation in fecundity, parental care, and offspring development. We compared the brood sizes and nestling mass and feather growth trajectories between orange-crowned warblers (Oreothlypis celata) breeding in Alaska versus California, and used 24-hour video recordings to study the relationship between parental care and growth rates. Per-offspring provisioning rates were highest in the smallest broods, and food delivery was positively correlated with nestling growth over the 24-hour period only in Alaska. Females in Alaska spend more time brooding, and juveniles there showed faster feather growth and earlier mobility compared with those in California. We also found differences in the energetic and...