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 nutritional content of insect larvae that could potentially facilitate the observed differences in nestling growth relative to food provisioning. Our results point to the potential importance of food quality and parental provisioning of warmth, in addition to food, for explaining avian growth patterns. We highlight the need to quantify multiple dimensions of parental care and of offspring growth and development, and to better understand the relationships between feather growth, nestling period length, and fledgling mobility. This article is protected by copyright. All rights reserved.
