Avian hatching patterns in response to low-quality breeding environments and ecological stochasticity: Adaptation or constraint?

Hatching patterns may be adaptations to optimize reproductive success in suboptimal breeding conditions, although the potential mechanisms remain unclear. Artificial eggs were used to control the onset of incubation to produce asynchronous or synchronous broods of mountain bluebirds (Sialia currucoides) breeding on food-limited reclaimed mine lands, which were compared to populations breeding in undisturbed habitat. Treatment was successful, but had negligible effects on nestling phenotype, suggesting environmental constraints may be responsible for hatching patterns in this species. Larger prey items and higher male condition also resulted in lower feeding rates for synchronous broods specifically. Broods of tree swallows (Tachycineta bicolor) that hatched synchronously experienced faster growth when they had higher parasite loads, but were lighter near fledging, providing support for the ‘tasty chick’ hypothesis. Overall, my results suggest that hatching patterns may be indicative of environmental challenges during breeding.