Camouflage and Clutch Survival in Plovers and Terns

Abstract

Animals achieve camouflage through a variety of mechanisms, of which background matching and disruptive coloration are likely the most common. Although many studies have investigated camouflage mechanisms using artificial stimuli and in lab experiments, less work has addressed camouflage in the wild. Here we examine egg camouflage in clutches laid by ground-nesting Snowy Plovers Charadrius nivosus and Least Terns Sternula antillarum breeding in mixed aggregations at Bahía de Ceuta, Sinaloa, Mexico. We obtained digital images of clutches laid by both species. We then calibrated the images and used custom computer software and edge detection algorithms to quantify measures related to three potential camouflage mechanisms: pattern complexity matching, disruptive effects and background color matching. Based on our image analyses, Snowy Plover clutches, in general, appeared to be more camouflaged than Least Tern clutches. Snowy Plover clutches also survived better than Least Tern clutches. Unexpectedly, variation in clutch survival was not explained by any measure of egg camouflage in either species. We conclude that measures of egg camouflage are poor predictors of clutch survival in this population. The behavior of the incubating parents may also affect clutch predation. Determining the significance of egg camouflage requires further testing using visual models and behavioral experiments.

A computer vision for animal ecology

“…For example, Stoddard et al. () developed edge detection algorithms to evaluate the relative camouflage of nesting shorebird species as compared to their nesting substrate (Figure b).…”

“…(2) From Stoddard et al. (), snowy plover ( Charadrius nivosus ) nest clutch (2a) segmented into egg and background regions (2b), edge detection was used to quantify edges (2c), in order to calculate the degree of egg camouflage compared to the background substrate (2d). See for credits and permissions [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…() and Stoddard et al. () were used under the PlosOne Creative Commons License. Thanks to Shanis Barnard, Drew Weber, Will Pearse, Margaret Kosmala, Tanya Berger‐Wolf, Chuck Stewart, J. J. Valletta and Oscar Beijboom for their helpful input.…”

“…By comparing image features, computer vision can be used to study animal camouflage (Tankus & Yeshurun, 2009) and biomimicry (Yang, Wang, Liang, & Møller, 2016). For example, Stoddard et al (2016) developed edge detection algorithms to evaluate the relative camouflage of nesting shorebird species as compared to their nesting substrate ( Figure 3b).…”

CeutaOPEN: Individual-based field observations of breeding snowy ploversCharadrius nivosus

“…1). Previously, we have used subsets of these data to report on a wide variety of topics in organismal biology, including sex ratio variation 12 , population viability 13 , courtship behaviour 14 , incubation behaviour 15 , parental care 16 , ontogeny 17 , chronobiology 18 , camouflage mechanisms 19 , offspring desertion 20 and mating system dynamics 21 . The motivation for making our database open is to provide evolutionary ecologists with an accessible resource that will serve as an important repository for addressing overarching questions in organismal biology and conservation.…”