Foraging Behavior and Predation Success of the Sand Viper (Cerastes Vipera)

520 Foraging behavior and predation success of the sand viper (Cerastes vipera) Aziz Subach, Inon Scharf, and Ofer Ovadia Abstract: Activity levels and foraging success of ectotherms are dependent both on extrinsic factors (e.g., ambient temperature) and intrinsic factors (e.g., hunger level). We focus here on activity and foraging of sand vipers (Cerastes vipera (L., 1758)) (Squamata: Viperidae) in the northwestern Negev desert of Israel. Viper activity is bounded by a specific thermal range, but within this range, temperature does not affect the distance moved. Movement distances are, however, positively correlated with relative humidity. The capture success of lizards, the main prey of this viper, is strongly related both to movement distances of the snake and to the number of the lizard burrows scanned. Body size and shape have a direct effect on the number of burrows scanned and on the number of lizards captured. The increase in capture success with size is probably due to the consequent increase in the range of prey items the sand viper can subdue or handle. Vipers are larger and have a higher mass to length ratio in one of the three study sites, characterized by higher mean annual rainfall and vegetation cover. Finally, females tend to have a higher mass to length ratio than males, which may provide some space within the female body for reproductive materials such as eggs. Re´sume´ : Les niveaux d’activite´ et de recherche de nourriture des ectothermes de´pendent a` la fois de facteurs extrinse`ques (par ex., la tempe´rature ambiante) et de facteurs intrinse`ques (par ex., l’intensite´ de la faim). Nous nous inte´ressons ici a` l’activite´ et la recherche de nourriture de la vipe`re des sables (Cerastes vipera (L., 1758)) (Squamata : Viperidae) dans le nord-ouest du de´sert du Ne´guev en Israe¨l. L’activite´ de la vipe`re est restreinte a` une gamme spećifique de tempe´ratures, mais dans cette gamme, la tempe´rature n’affecte pas la distance des de´placements. Il y a cependant une corre´lation positive entre la distance des de´placements et l’humidite´ relative. Il existe une forte relation positive entre le succe`s de la capture de le´zards, les proies principales de cette vipe`re, et a` la fois la distance des de´placements du serpent et le nombre de terriers de le´zards examine´s. La taille et la forme du corps ont un effet direct sur le nombre de terriers examine´setle nombre de le´zards capture´s. L’accroissement des captures en fonction de la taille s’explique probablement par l’augmen- tation relieéa` la taille de l’entendue des types de proies que la vipe`re des sables peut maıˆtriser ou` manipuler. Les vipe`res sont plus grandes et posse`dent un rapport masse/longueur plus e´leve´ dans l’un des trois sites d’e´tude, caracte´rise´ par des prećipitations moyennes annuelles plus e´leveés et une couverture ve´ge´tale plus importante. Enfin, les femelles ont tendance a` avoir un rapport masse/longueur plus e´leve´ que celui des maˆles, ce qui peut fournir aux femelles de l’espace a` l’inte´rieur du corps pour les produits de la reproduction, tels que les œufs. [Traduit par la Re´daction] Introduction expected to spend less time foraging (e.g., Peterson et al. 1993; Vincent and Mori 2008). It is also possible that cold All foraging activities of animals are affected by a variety habitats may have an indirect effect on foraging success via of extrinsic factors (Bell 1990) like prey density and spatial habitat selection (i.e., they reduce the suitability of certain distribution (e.g., Bond 1980), ambient temperature and hu- places like ambush sites; Shine et al. 2002). Effects of other midity (e.g., Peterson et al. 1993; Angilletta et al. 2002), and environmental factors such as humidity, although less well level of illumination, cloudiness, and amount of solar radia- studied, were also shown to influence snake behavior, habi- tion (e.g., Kotler et al. 1994). In ectotherms, abiotic factors tat selection, and foraging success (Daltry et al. 1998; like ambient temperature are especially important (Angilletta Moore and Gillingham 2006). All foraging activities of ani- et al. 2002) at times of searching and foraging during the mals are also affected by intrinsic factors (Bell 1990) like diel cycle; however, these factors may also play a central hunger or satiation level (e.g., Bond 1980) and reproductive role in determining dominant life-history traits such as state (e.g., Gibbons and Semlitsch 1987). Animals deprived growth rate and adult body mass (Atkinson and Sibly 1997; of food may use two alternative behavioral–physiological Bronikowski 2000). For example, in cool environments, strategies: (1) either increase activity with the aim to locate snakes may be less effective in capturing prey and are thus new patches or (2) decrease activity to save energy and wait for an increase in food availability (Gutman et al. 2007). Received 25 February 2009. Accepted 1 April 2009. Published on the NRC Research Press Web site at cjz.nrc.ca on 3 June Sand vipers are particularly appropriate animal models for 2009. studying foraging behavior, simply because they are easy to follow. Snakes, in general, are found in a diverse range of 1 A. Subach, I. Scharf, and O. Ovadia. Department of Life habitats, where they are highly dependent on their immedi- Sciences, Ben-Gurion University of the Negev, POB 653, Beer- ate surroundings (e.g., substratum and microclimate; Lilly- Sheva 84105, Israel. white and Henderson 1993), and can therefore be used for 1Corresponding author (e-mail: [email protected]). studies of local adaptations. Yet, studies of snake foraging Can. J. Zool. 87: 520–528 (2009) doi:10.1139/Z09-034 Published by NRC Research Press Subach et al. 521 behavior usually relate only to one or two factors that could creases the chances of the vipers being preyed upon and affect foraging behavior and success (but for more compre- also increases activity of potential widely foraging prey. hensive studies see Moore and Gillingham 2006; Crnobrnja- Furthermore, cloudiness is often positively correlated with Isailovic et al. 2007). temperature and humidity, which in turn should increase ac- In this study, we used the sand viper (Cerastes vipera (L., tivity. 1758)) (Squamata: Viperidae) as a model species to study We also expected a strong positive correlation between the effects of extrinsic microclimatological factors, such as activity level and capture success of prey items. As the viper temperature and humidity, and of intrinsic factors, such as moves longer distances, it increases the probability of en- body mass, length, and sex, on foraging activity and capture countering lizard burrows just by chance. While studying success of prey. The sand viper is an interesting example of capture success, we also took some intrinsic factors into a predator switching from the active foraging mode to the consideration such as sex and body mass, and thus could ambush mode. Specifically, it adopts an actively searching test for their effect on activity and capture success. Finally, foraging mode during most of the night and is inactive dur- we predicted that body dimensions should be positively cor- ing most of the day; however, during the day–night transi- related with both activity level and capture success. Larger tions (dawn and dusk), it adopts an ambush mode waiting individuals should consume more prey items, because their for lizards to enter its attack radius (A. Subach, personal ob- larger size allows them to feed on a wider variety of prey servations). It is likely that as dawn begins the cost of (Arnold 1993). They should be also more active (this is true movement increases with temperature faster than the poten- at least for terrestrial mammals under field conditions; Swal- tial benefit, and therefore a sit-and-wait foraging mode is low et al. 1999). The mass to length ratio may indicate the adopted. When temperature and direct solar radiation in- physiological state of the viper, i.e., vipers in good condition crease substantially, the sand viper seeks a shelter inside ro- show higher mass to length ratios (Shine et al. 2003). Con- dent burrows and ceases its activity. At dusk, both direct sequently, those individuals should invest less in foraging solar radiation and temperature decrease considerably allow- than others with a lower mass to length ratio. ing the snake to exit its shelter and to wait in an ambush The data collected also enabled us to perform morpholog- mode until night begins and the active foraging mode be- ical comparisons involving sexual-size dimorphism (SSD), comes preferable again. Most reptiles adopt a distinct forag- and viper size (length) and shape (mass to length ratio) ing mode, but species that switch between foraging modes across different study sites. We predicted that females are not rare. This switch may be related to satiation level, should be larger and have a higher mass to length ratio than prey density, and habitat structure (e.g., Huey and Pianka males. We also predicted that vipers in study sites, charac- 1981; Mullin et al. 1998; Greeff and Whiting 2000; Verwai- terized by higher levels of mean annual rainfall and vegeta- jen and Van Damme 2008). This plasticity aids reptiles to tion cover, should be larger and show a higher mass to forage on more than one prey item (Mullin et al. 1998; length ratio. Indeed, in about two-thirds of studied species, Greeff and Whiting 2000). female snakes were larger; the main reason for this size dif- We report here on the relationships between activity of ference is the longer maturation period in females (Shine sand vipers, including foraging success and environmental 1993).

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