Abstract:Attacks by big cats on livestock are one of the major causes of human-felid conflicts and, therefore, an important factor in the conservation of these species. it has been argued that a reduction in natural prey abundance promotes attacks on domestic species, but few studies have tested this statement, and some have delivered contradictory results. We investigated whether the occurrence of attacks to livestock by jaguar and puma relates to the abundance and richness of their natural prey. in the rainy season 2009, we tracked potential prey species counting signs of presence along linear transects in 14 non-attacked cattle farms (control) and in 14 attacked cattle farms in NW Costa Rica. There was a negative relationship between the occurrence of attacks and both species richness (p=0.0014) and abundance (p=0.0012) of natural prey. Our results support the establishment of actions to promote support and recovery of natural prey, in order to diminish attacks on livestock, while maintaining jaguar and puma populations. Rev. Biol. Trop. 62 (4): 1459-1467. Epub 2014 December 01.Key words: human-wildlife conflicts, livestock depredation, Costa Rica, jaguar, prey abundance, puma, species richness.Habitat loss and fragmentation are among the major causes behind biodiversity loss (Tilman et al., 2001). Since top predators require large territories and a relatively high and diverse abundance of prey species (Linnell, Swenson, & Andersen, 2001;Macdonald & Sillero-Zubiri, 2002), they are especially sensitive to landscape changes, and most of their populations are already restricted to protected areas (Michalski, Boulhosa, Faria, & Peres, 2006). increased interaction between people and big cats, like the jaguar (Panthera onca) and the puma (Puma concolor) tends to escalate conflicts (Saberwal, Gibbs, Chellam, & Johnsingh, 1994;Treves & Karanth, 2003;Kissling, Fernández, & Paruelo, 2009).Large cat attacks on domestic animals are one of the main reasons for conflict with humans due to economic losses for local communities (Hoogesteijn, Hoogesteijn, & Mondolfi, 1993;Palmeira & Barrella, 2007;inskip & Zimmermann, 2009). Palmeira (2004 in Brazil, estimated the loss attributable to jaguars as 25 865USD in six years in one big cattle farm, while 50 small farms in Northern Costa Rica recorded total cattle losses of 9 065USD, during one and a half year, when including both jaguar and puma attacks (Amit, GordilloChavez, & Bone, 2013). Despite these tangible losses in that study, perception of damage overestimated real losses, implying the relevance of social and educational factors when addressing these issues.Frequently, big cats are considered a problem by farmers, who directly retaliate on predators to minimize the incidences on livestock, thus contributing to the decline of the felid populations (Weaver, Paquet, & Ruggiero, 1996;Treves & Naughton-Treves, 2005;inskip & Zimmermann, 2009). However, top predators like big cats, have an important role in the ecosystem regulation. Their extinction may entail severe effects in ec...