The Evolution of Nest Sharing and Nest Mate Killing Strategies in Brood Parasites

Abstract

Chicks of avian brood parasites either cohabit with host nestlings (e.g., cowbirds, non-evictor cuckoos) or eventually eliminate their potential competitors and are raised as the sole inhabitants of the foster parents’ nest. This latter phenomenon, termed as direct killing, involves the young brood parasitic chick evicting all other eggs or hatchlings from the nest (e.g., evictor cuckoos) or killing their nest mates with their bill hook (e.g., honeyguides) and monopolize all food resources delivered by host parents. We overview the types of variability in parasite chick strategies toward nest mates and also discuss the potential reasons why competition vs. eviction behaviors have evolved in different parasitic lineages. We explore the possibility that one of the key factors for the evolution of nest mate acceptance versus direct killing was the virulence of the parasitic chick in relation to host nestling (competitive ability) and the ability to manipulate provisioning by the host parents. For extensive life history studies of the conflict between unrelated hosts and brood parasitic nestlings, we suggest that additional avenues for future research should explore and understand why and how evolutionary adaptations of brood parasitic nestlings have evolved.