# Matching Multiple Backgrounds: Egg Camouflage Across Different Habitats in a Shorebird

## TL;DR

Kentish plover eggs are camouflaged against predators by matching the average color of their habitats, not by adapting to specific local patterns.

## Contribution

The study shows that nest-site selection, not egg pattern adaptation, enables effective camouflage across different habitats.

## Key findings

- Egg patterns make them more detectable at close range, but they are cryptic at a distance.
- Egg colors match overlapping background colors between habitats, not specific local colors.
- Nest-site selection within each habitat allows for effective camouflage despite habitat differences.

## Abstract

For species found in multiple habitats, the problem of camouflage against visually different backgrounds can be challenging. This is particularly so for bird eggs in open nests, as the scope for movement or alternative defensive strategies is limited. We studied egg camouflage in a small shorebird, the Kentish plover Anarhynchus alexandrinus, in two different coastal habitats in Cádiz province, Spain: sandy beaches and saltmarshes. Using calibrated photographs taken in situ and neurophysiologically plausible models of colour and pattern vision, we assessed the predicted discriminability of egg colour and patterning from those of backgrounds for likely nest predators (avian and mammalian carnivore) and, for comparison, humans. The findings suggest that at close range
A. alexandrinus
eggs are more susceptible to detection by visual predators based on their patterns (aka visual texture) rather than their colours, but at distances beyond which individual pattern elements can be resolved, they are highly cryptic. Although the colours and patterns of the saltmarsh and beach nest sites differ, the colours and surface patterning of eggs do not, suggesting that there is no local adaptation. However, the colours of eggs are similar to the types of background colours that overlap between the beach and saltmarsh. This suggests that, although the gross visual appearances of beach and salt marsh are quite different, egg camouflage in Kentish plovers relies on behavioural nest‐site selection and a good colour match to the average location type. The maculation on the eggs does not appear to represent background matching in terms of pattern, so its function remains speculative.

We studied egg camouflage in Kentish plovers nesting in two visually distinct habitats, sandy beaches and salt marshes, in southern Spain. Despite initial expectations of local adaptation or compromise camouflage, the birds instead chose nest sites within each habitat that shared overlapping colour and visual texture characteristics, allowing effective camouflage from predators, especially at a distance. Our study exemplifies the importance of determining the confusability (misclassification) of whole distributions of prey and background features, not just the differences in the means of those distributions or the perceptual differences between particular colours.