Rattlesnake colouration affects detection by predators M. V. Harmel* , H. L. Crowell † , J. M. Whelan & E. N. Taylor Biological Sciences Department, California Polytechnic State University, San Luis Obispo, CA, USA Keywords colouration; Crotalus oreganus helleri; crypsis; pit viper; predation risk; clay models. Correspondence H. L. Crowell, Ecology and Evolutionary Biology Department,University of Michigan, 1105 N. University Ave., Ann Arbor, MI, 48109, USA Email: hlcrowel@umich.edu *Jekyll Island Authority Conservation Department, Jekyll Island, 100 James Road, GA, 31527,USA † Ecology and Evolutionary Biology Department, University of Michigan, 1105 N. University Ave., Ann Arbor, MI, 48109,USA Editor: Mark-Oliver R€ odel Associate Editor: Anthony Herrel Received 13 May 2019; accepted 12 March 2020 doi:10.1111/jzo.12786 Abstract Crypsis, or the ability of an animal to avoid detection by other animals, is strongly impacted by an animal’s colouration and pattern. Crypsis may be especially impor- tant for ambush foragers, which spend much of their time above ground and there- fore benefit from being inconspicuous to predators and prey. The purpose of this study was to investigate the effect of rattlesnake skin colouration on the likelihood of it being detected and attacked by a predator, on the latency (time) to attack, and on the attack frequency on each physical body section of the models. Clay models representing four commonly observed rattlesnake colour morphs (light, dark and two intermediate colour patterns) were deployed in two different habitat types (wooded area and open field), and the marks made on the models by predators were quantified over time. We found that light snake models, which have little contrast with substrate, were less likely to be attacked and were attacked later than darker model types, which have higher contrast with substrate. Predators attacked the various body segments of the models at similar frequencies. Our data suggest dark-coloured rattlesnakes, which have the most contrast with the golden-coloured grasses and therefore have the lowest crypsis, are most at risk from predation. Introduction Colour and its perception by organisms has been of long-standing interest to biologists studying predator and prey species alike (Thayer, 1918; Carter, 1948; Endler, 1978; Brodie & Janzen, 1995; Hinman, Throop & Adams, 1997; Kikuchi & Pfennig, 2010; Farallo & Forstner, 2012). An organism’s bold pattern or bright colouration can cause pause and warrant investigation or avoidance by other organisms, while colouration and patterns that blend with the landscape can aid the animal in crypsis or avoid- ance of detection by predators (Endler, 1978; Stevens & Meri- laita, 2009; Schaefer & Stobbe, 2006; Mart  ınez-Freir  ıa et al., 2017; Merilaita, Scott-Samuel & Cuthill, 2017; Cuthill, 2019). Cryptic colouration may be especially important for animals that rely on ambush to capture prey. Not only does their colouration allow ambush foragers to successfully avoid detection by prey (Godfrey, Lythgoe & Rumball, 1987; Greco & Kevan, 1994), but also given that they often spend extended periods of time above ground and immobile while foraging, cryptic colouration may assist these animals in evading detection by predators (Isaac & Gregory, 2013). Rattlesnakes have emerged as model organisms for the study of ambush foraging behaviours in part due to modern technologies that allow scientists to observe behaviours remo- tely (Clark, 2006). Although the roles of colour in diverse topics ranging from sexual dichromatism to Batesian mimicry have been studied in several species of snakes including the common garter snake (Thamnophis sirtalis), coral snakes (Micrurus and Micruroides), hog-nosed snakes (Heterodon nasicus) and European Vipera species, there are few studies investigating the role of colour in ambush foraging rattlesnakes (Edgren, 1957; Smith, 1975; Brodie & Janzen, 1995; Capula & Luiselli, 1995; Hinman et al., 1997; Bittner, 2003; Santos et al., 2014; Mart  ınez-Freir  ıaet al., 2017). Farallo & Forstner (2012) found that rattlesnake models with patterns more dis- similar to the surrounding substrate were attacked at higher fre- quencies than models that blended in with substrate. Numerous techniques have been developed to investigate the effect of animal colouration on detection by predators (Smith, 1975; Brodie & Janzen, 1995; Hinman et al., 1997; Bittner, 2003; Kikuchi & Pfennig, 2010; Farallo & Forstner, 2012; Cuthill et al., 2017; Winebarger, 2017). It is difficult to quantify pre- dation attempts on live snakes due to experimental design con- straints; furthermore, the variation in behaviour of live snakes when confronted with predators could confound any effects specifically of colour on predation. As a result, researchers Journal of Zoology  (2020) – ª 2020 The Zoological Society of London 1 Journal of Zoology. Print ISSN 0952-8369