The Role of Behaviour in Camouflage and Thermal Regulation of Ground-Nesting Birds

Abstract

Animal coloration frequently functions as camouflage, allowing animals to avoid detection through diverse strategies. Given the dynamic nature of their visual environments, effective camouflage requires animals to interact with their surroundings, often through behaviours such as selecting and modifying their background. Birds, facing survival challenges such as predation and egg overheating, exhibit behaviours influenced by these challenges. However, our understanding of behaviorally enhanced camouflage strategies for eggs, chicks, and adults, along with the associated survival benefits and underlying mechanisms, remains limited. In this thesis, I conducted research on ground-nesting birds using digital photography and predator visual modelling. I investigated the role of individual behaviour in the camouflage of egg, chick, and adult stages across spatial and temporal scales. Additionally, I investigate potential trade-offs between egg camouflage and thermal regulation in nest substrates selectively chosen or modified by parents. Furthermore, I examined the mechanisms controlling background choice behaviour for egg camouflage. My findings reveal that background choice and nest substrate modifications improve camouflage across all bird life stages, as well as nest-to-background camouflage. Background choice exhibits sex-specific patterns, with females demonstrating better camouflage at nests than males. Additionally, nest substrate choice enhances egg camouflage more effectively than it does for adults. Chick feathers aid in generalist background matching, and adults and chicks adjust escape responses based on feather camouflage. Despite temperature and circadian rhythm influences, birds maintain a balance between camouflage and egg thermal regulation. Moreover, egg but not adult camouflage at the selected nest improved clutch survival. My investigation highlights the role of learning egg appearance and potentially genetic control in enabling females to select backgrounds that enhance egg camouflage. These results emphasise the critical importance of bird behaviour in the realm of camouflage, underscoring ground-nesting birds' survival and adaptability in challenging environments.