Hidden in plain sight: camouflage and hiding behaviour of wild precocial chicks in an open landscape

Abstract

Camouflage represents an important component of self-protection when animals cannot easily evade predators and is often altered by behavioural responses to a predation threat. The cryptic plumage of many precocial chicks inspired early theoretical work on camouflage mechanisms, but so far, limited efforts have gone towards empirically testing the crypsis of chick plumage properties in their natural environment. We studied background matching and hiding behaviour in precocial snowy plovers Charadrius nivosus in Bahia de Ceuta, Northwest Mexico. This ground-nesting wader breeds in sparsely vegetated open habitats such as salt flats and sandy beaches. The open habitats provide a challenge for young chicks to evade predator detection. Examining background matching of wild chicks for luminance, pattern and colouration at their hiding spots, we found that chicks matched the luminance of their chosen spot better than at unchosen nearby spots. Pattern and colouration matching were age-related, with the plumage of older chicks matching their hiding spots better than those of recently hatched chicks. This suggests that with increasing mobility, chicks may be better able to find hiding places that optimise camouflage. Finally, we found that chicks were more likely to hide in soil cracks than expected by chance, suggesting that chicks chose these soil features in a barren landscape as preferred hideouts. We conclude that the cryptic plumage is an understudied but essential part of the anti-predator repertoire of precocial chicks. The plumage most likely works hand-in-hand with the anti-predator behaviours of chicks and their parents to increase survival chances of precocial young. Significance statement Many chicks rely on effective camouflage to evade predators and survive until fledging. We studied how plumage characteristics and behavioural choices enable snowy plover chicks to hide effectively from approaching predators in an open landscape. These chicks leave their nest scrapes shortly after hatching, relying on their cryptic plumage for several weeks to evade predator detection. We found that chicks chose hiding spots where their plumage had a higher match in luminance and, for older chicks, a higher match in pattern and colouration than at adjacent spots. When available, chicks chose to hide in small cracks that appeared in the soil from the evaporation of moisture. This study represents the first quantitative characterisation of cryptic chick plumage features in a natural population. Our results demonstrate that plumage and behavioural responses jointly contribute to the effective camouflage of small chicks.