ORIGINAL PAPER Foraging tactics of an ambush predator: the effects of substrate attributes on prey availability and predator feeding success Edna González-Bernal & Gregory P. Brown & Elisa Cabrera-Guzmán & Richard Shine # Springer-Verlag 2011 Abstract The foraging sites selected by an ambush forager can strongly affect its feeding opportunities. Foraging cane toads (Rhinella marina) typically select open areas, often under artificial lights that attract insects. We conducted experimental trials in the field, using rubber mats placed under lights, to explore the influence of substrate color and rugosity on prey availability (numbers, sizes, and types of insects) and toad foraging success. A mat's color (black vs. white) and rugosity (smooth vs. rough) did not influence the numbers, sizes, or kinds of insects that were attracted to it, but toads actively preferred to feed on rugose white mats (50% of prey-capture events, vs. a null of 25%). White backgrounds provided better visual contrast of the (mostly dark) insects, and manipu- lations of prey color in the laboratory showed that contrast was critical in toad foraging success. Insects landing on rugose backgrounds were slower to leave, again increasing capture opportunities for toads. Thus, cane toads actively select backgrounds that maximize prey-capture opportuni- ties, a bias driven by the ways that substrate attributes influence ease of prey detection and capture rather than by absolute prey densities. Keywords Foraging success . Prey choice . Prey selection . Bufo marinus . Sit-and-wait predation Introduction For any mobile predator, a primary determinant of foraging success is the selection of sites in which to search for prey. Often, the numbers of prey and their vulnerability to the predator show strong spatial hetero- geneity, such that we might expect predators to evaluate potential foraging sites carefully before choosing specific hunting locations (Adams 2000; Heiling 1999; Hopcraft et al. 2005; Inoue and Matsura 1983; Scharf and Ovadia 2006). The choice of a foraging site is especially significant in the case of a sit-and-wait (ambush) forager, because many such animals spend very long periods at a single site—and hence, their food intake over a substantial time period is determined by foraging success at that site (Eskew et al. 2009; Heinrich and Heinrich 1984; Webb and Shine 1998a,b). Optimality theory thus predicts that natural selection will have fine-tuned foraging-site choice criteria of ambush predators, such that these animals choose sites that maximize their opportunities for prey capture (Pyke 1984; Pyke et al. 1977). What criteria might ambush predators use to select foraging sites, and why? Answers to those questions may give insights into important features of predator ecology, including dispersion patterns, feeding rates, and effects of anthropogenic habitat change on predator viability. An extensive body of natural history literature (much of it anecdotal) suggests that ambush predators of a diverse array of phylogenetic lineages utilize similar criteria in selecting foraging sites. Such predators exploit temporal and spatial heterogeneity in prey availability by lying in wait at sites where prey are (a) more frequently encountered and (b) less capable of detecting or avoiding the predator. For example, some spiders construct their webs near Communicated by P. Bednekoff E. González-Bernal : G. P. Brown : E. Cabrera-Guzmán : R. Shine (*) School of Biological Sciences A08, University of Sydney, Sydney, NSW 2006, Australia e-mail: rick.shine@sydney.edu.au Behav Ecol Sociobiol (2011) 65:1367–1375 DOI 10.1007/s00265-011-1147-9 Received: 9 August 2010 / Revised: 3 January 2011 / Accepted: 25 January 2011 / Published online: 17 February 2011