Implications of Nest Sanitation in the Evolution of Egg Rejection

Abstract

Nest sanitation or nest cleaning behaviour in Passeriformes has been widely reported in the literature. It was proposed that this behaviour is a preadaptation for the evolution of egg rejection behaviour in hosts of avian brood parasites, which are primarily passerines. Indeed, the same motor skills underlie nest sanitation and egg rejection behaviours. This “nest sanitation hypothesis” predicts that non-egg-shaped objects (i.e. simulated debris) are rejected more frequently than egg-shaped objects (i.e. simulated parasitic eggs), and the frequency of rejection mirrors the expected frequency of debris falling into the nest, rather than the risk of parasitism. We update information on nest sanitation processes (e.g. timing of defecation relative to faecal sac removal) and synthesize lists of objects removed from nests by passerines in non-experimental and experimental contexts. In the former, passerines remove various objects from their nests, including faecal sacs, parasitic invertebrates, vegetation and dead nestlings. Results of experiments reveal that non-egg-shaped objects, especially those most resembling debris, were more frequently rejected from nests, and that rejection of non-egg-shaped objects was generally constant among nesting stages prior to hatching.