No Evidence That Nest Cover Shapes Incubation Schedules in a Mediterranean Shorebird Population

Nest site selection is a key reproductive decision in ground-nesting birds, given its direct consequences for breeding success and survival of the parent(s). Studies in extreme hot environments show that cover (e.g., vegetation, rocks) that provides shade at the nest can strongly shape parental incubation behaviour. Understanding the generality of these effects across differing environments, including less extreme climates, is an important goal in predicting the behavioural and reproductive impacts of rising global temperatures. Here we investigated how nest cover influences biparental incubation effort and sex-specific investment in a wild population of Kentish Plovers breeding in a Mediterranean environment. We used 24-h video recordings from 24 nests with variable nest cover that ranged from fully open (0% coverage) to complete coverage (100%). Contrary to previous work that indicates less covered nests require more parental effort to shield embryos from thermal extremes, we found that nest cover was not associated with total incubation, mean off-nest duration, or male incubation share. However, we detected a non-significant trend for a higher frequency of off-nest periods in more covered nests. Our results suggest that nest cover is not a strong modulator of incubation behaviour in our population, suggesting that in some circumstances nest cover may primarily impact aspects of incubation other than thermoregulation, such as protection from visual predators, wind exposure or precipitation. Despite no observed difference in incubation patterns, we cannot preclude the possibility that parents nesting in low cover sites are exposed to greater heat stress, but such heat stress and physiological costs are not reflected in changes in incubation. We propose comparative studies of biparental ground-nesting species across climatic gradients to identify the adaptations associated with breeding in hot climates that include behaviour, heat tolerance and nest cover.