Elsevier

Animal Behaviour

Volume 104, June 2015, Pages 197-202
Animal Behaviour

The role of body shape and edge characteristics on the concealment afforded by potentially disruptive marking

https://doi.org/10.1016/j.anbehav.2015.03.027Get rights and content

Highlights

  • Boundary and shape properties are important for predators to recognize their prey.

  • We address the untested hypothesis that disruptive coloration distorts outlines.

  • We show that edge markings increase survivorship, dependent on boundary visibility.

  • Surprisingly, concealment provided by edge markings is not dependent on shape.

  • We argue that edge markings function as disruptive coloration, independent of crypsis.

Disruptive coloration is a camouflage strategy proposed to function by breaking up an animal's boundary and mask its characteristic shape, thereby impairing its recognition by onlookers. Recent studies on disruptive coloration have consistently shown an association between putative ‘disruptive’ edge coloration and heightened survivorship, but the underlying mechanism is unclear. If edge markings enhance survivorship through disruption, then the success of this camouflage strategy should depend on the visibility of the animal's boundaries and its shape. Here, we experimentally tested the hypothesis that the disruptive camouflage of a prey improves its survivorship in a manner that is conditional on the visibility of its boundaries and its overall shape. We found that both boundary visibility (solid versus translucent boundary) and boundary shape (straight versus ruffled outlines) affected survivorship of artificial moths in a human computer-foraging task. Furthermore, as expected, the observed survival benefits of edge markings were conditional upon the boundaries' visibility. Surprisingly, however, no such interaction was found between edge markings and body shape on overall survivorship. Therefore, it remains uncertain whether disruptive edge markings affect shape perception per se. Collectively, however, our results add further support to the contention that edge markings provide camouflage by breaking up an animal's boundaries in a manner independent of background matching.

Section snippets

Experimental Protocol

A Microsoft Visual Basic Express® 2008 (Microsoft Corp., Seattle, WA, U.S.A.) program presented cryptic moth targets superimposed on photographs of trees on a computer screen to volunteer human subjects (Webster, Callahan, Godin, & Sherratt, 2009). All participants were visitors to Carleton University's Maxwell MacOdrum Library, where the testing took place. Computer monitors (1900 × 1200 pixels) were rotated to a portrait orientation to display high-resolution grey-scaled tree images (1600 × 800

Experiment 1

We observed a significant main effect of moth target coloration (presence/absence of edge-intersecting patches) on both target survivorship (Table 1, Fig. 3a) and target search time (Table 1, Fig. 3b). Therefore, the presence of edge-intersecting patches is associated with heightened survivorship and, of those targets that were discovered, a longer search time before detection. There was also a significant main effect of boundary visibility on both moth target survivorship (Table 1, Fig. 3a)

Discussion

Our study builds on the body of evidence that edge markings on prey affect their rate of detection by visually hunting predators (Cuthill et al., 2000; Cuthill et al., 2005; Cuthill & Székely, 2009; Fraser et al., 2007, Merilaita and Lind, 2005, Schaefer and Stobbe, 2006, Stevens et al., 2006, Stevens et al., 2009). However, it remains uncertain whether edge markings on prey increase their concealment through their effect on disrupting edge detection or through some other visual or cognitive

Acknowledgments

We are very grateful to the staff of Carleton University's Maxwell MacOdrum Library for their hospitality in hosting our human-predator experiments and to the students who participated in these experiments. All authors designed the experiment and were involved in writing the manuscript. R.J.W. ran the experiment and performed the analysis. This research was supported by Discovery grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) to J.-G.J.G. and T.N.S. We

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