The influence of egg presence and eggshell colour in the attraction of visually oriented predators to nests of a tropical forest bird

Abstract

Several hypotheses have been proposed to account for the function of eggshell pigmentation. One predicts that patterns of colour and markings provide camouflage against visually oriented nest predators. However, the effectiveness of any anti‐predatory function of eggshell colour may be reduced if predators can use the nests per se as foraging cues (nest‐crypsis hypothesis). Here, we tested whether eggshell pigmentation, and a set of concurrent variables, could explain nest predation in natural nests of the Atlantic Forest endemic Blue Manakin Chiroxiphia caudata containing plasticine eggs. Nests were continuously monitored for predator identification using infra‐red camera traps, and we considered the nest‐crypsis hypothesis by testing the premise that if predators can use nests as visual cues, they would be recorded checking empty nests at rates similar to those containing eggs. Six bird species were identified as visually oriented predators of nest contents, and predation frequencies were low and not influenced by eggshell colour. Empty nests and nests containing eggs were visited by predators at similar frequencies, independently of eggshell colour, which provided the first direct support for the nest‐crypsis hypothesis. It suggests that for this tropical forest, open‐nesting passerine, selective forces driving nest concealment and nest camouflage may be stronger than selection for eggshell colour variation.