Hiding in plain sight: a study on camouflage and habitat selection in a slow-moving desert herbivore

Abstract

Camouflage via animal coloration and patterning is a broadly important antipredator strategy. Behavioral decision making is an influential facet of many camouflage strategies; fitness benefits often are not realized unless an organism selects suitable backgrounds. Controlled experimental studies of behavioral strategies in selection of backgrounds conferring camouflage, however, are rarely paired with observations of wild populations. In order to investigate how substrate composition influenced habitat preference and selection by juvenile desert tortoises (Gopherus agassizii), we completed a manipulative experiment in captivity and an observational study in the wild. In our captive experiment, we found that tortoises spent a greater portion of their time near rocks. We similarly found that wild tortoises preferentially placed themselves in areas with equivalent or larger-sized rocks. Additionally, juvenile tortoises were found to be less detectable on rock substrate by observers than they were on substrate-lacking rocks. We hypothesize that rocks improve juvenile tortoise camouflage and thus that tortoises select for habitat containing rock substrate, in part, due to a survival advantage conferred by such use. The desert tortoise is a threatened species, and the present study provides a model for examining the intersection between behavior and conservation, with implications for how suitable habitat is defined and measured in species conservation programs.

The key role of behaviour in animal camouflage

“…This includes species with preferences for rocky areas over uniform sand and a camouflage strategy that may involve resembling rocks and stones (masquerade; Cooper & Sherbrooke, ). Similar results have been found in tortoises (Nafus et al, ). Studies manipulating aspects like vegetation cover also report that ground‐nesting birds choose backgrounds related to camouflage and predation risk (Swaisgood et al, ; see Section II.1 c ).…”

Background matching and camouflage efficiency predict population density in four-eyed turtle ( Sacalia quadriocellata )

“…Camouflage is an interface among anti-predation behavior, habitat suitability, and conservation (Nafus et al, 2015). Both color quantity and score of camouflage in this study were based on the vision of humans, who are potential predators to the turtles.…”

“…Moreover, archeological records indicate that freshwater turtles were an important resource to early peoples of China for thousands of years (Fan and Zhang, 2008), and they continue to be hunted from this stream owing to their use as Chinese medicines and sources of foods (Shi et al, 2002;Dharmananda, 2005). Additionally, Nafus et al (2015) suggested that humans depend on their vision to detect turtles. Therefore, the four-eyed turtle is thought to be faced with predation pressure of visual predators, especially humans, in Hezonggou stream.…”

Active background choice facilitates crypsis in a tropical crab

“…For example, peppered moths Biston betularia, Peacock flounders Bothus mancus , desert tortoises Gopherus agassizii , and wall lizards Podarcis erhardii actively choose microhabitats that best maintain camouflage (Nafus et al . , Tyrie et al . , Marshall et al .…”