1 3 Oecologia DOI 10.1007/s00442-013-2760-2 COMMUNITY ECOLOGY - ORIGINAL RESEARCH Predator facilitation or interference: a game of vipers and owls Keren Embar · Ashael Raveh · Ishai Hoffmann · Burt P. Kotler Received: 21 November 2012 / Accepted: 22 August 2013 © Springer-Verlag Berlin Heidelberg 2013 on each other. In the foraging game context, they improve each other’s patch quality and hunting success. Keywords Optimal foraging · Predator interactions · Risk management · Behavioral tools · Community ecology Introduction In a community of predators, one predator may sometimes hinder or facilitate another’s hunting success. Therefore, the effect of two predator species in an ecological system cannot be predicted as simply the sum of their individual effects from two-way interactions (Sih et al. 1998). This adds complexity to the intricate predator–prey foraging game, where the prey have to manage predation risk from multiple sources, while the predators have to consider not only the behavior of their prey but also the behaviors of their competitors and the ensuing consequences. Predators may hinder each other in several ways. They may cause resource depression, either directly by consum- ing food or indirectly by scaring prey and causing them to reduce activity, increase vigilance, or seek refuge (Charnov et al. 1976). In addition, predators may hinder each other as potential risk of injury and death for the inexperienced. Webster et al. (2010) describe how lions eavesdrop on wild dog calls and kill any they can catch, and Sunde (2005) found that most young tawny owls die from predation by foxes and raptors. Predators may instead facilitate each other when one predator’s actions or responses to them expose the prey to higher risk of mortality by another predator (Kotler et al. 1992). “Predator facilitation” was coined by Charnov et al. to refer to the phenomenon where predator species inter- act synergistically. Losey and Denno (1998) reviewed, Abstract In predator–prey foraging games, the prey’s reaction to one type of predator may either facilitate or hin- der the success of another predator. We ask, do different predator species affect each other’s patch selection? If the predators facilitate each other, they should prefer to hunt in the same patch; if they interfere, they should prefer to hunt alone. We performed an experiment in a large outdoor vivarium where we presented barn owls (Tyto alba) with a choice of hunting greater Egyptian gerbils (Gerbillus pyra- midum) in patches with or without Saharan horned vipers (Cerastes cerastes). Gerbils foraged on feeding trays set under bushes or in the open. We monitored owl location, activity, and hunting attempts, viper activity and ambush site location, and the foraging behavior of the gerbils in bush and open microhabitats. Owls directed more attacks towards patches with vipers, and vipers were more active in the presence of owls. Owls and vipers facilitated each oth- er’s hunting through their combined effect on gerbil behav- ior, especially on full moon nights when vipers are more active. Owls forced gerbils into the bushes where vipers preferred to ambush, while viper presence chased ger- bils into the open where they were exposed to owls. Owls and vipers took advantage of their indirect positive effect Communicated by Peter Banks. Electronic supplementary material The online version of this article (doi:10.1007/s00442-013-2760-2) contains supplementary material, which is available to authorized users. K. Embar (*) · A. Raveh · I. Hoffmann · B. P. Kotler Mitrani Department of Desert Ecology, Blaustein Institutes for Desert Research, Ben Gurion University of the Negev, Sde Boker Campus, 84990 Midreseht Ben-Gurion, Israel e-mail: embar@bgu.ac.il; embarkeren@gmail.com