ORIGINAL PAPER Local enhancement and social foraging in a non-social insular lizard Ana Pe ´rez-Cembranos • Valentı ´n Pe ´rez-Mellado Received: 29 September 2014 / Revised: 11 December 2014 / Accepted: 16 December 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract Even in solitary foragers, conspecifics can provide reliable information about food location. The insular lizard Podarcis lilfordi is a solitary species with high population densities that sometimes aggregate around rich food patches. Its diet includes novel and unpredictable resources, such as carcasses or plants, whose exploitation quickly became widespread among the population. We tested the use of social information by lizards through some field experiments in which they had to choose one of the two pieces of fruit. Probably due to local enhancement, lizards preferred to feed on the piece of fruit where con- specifics or lizard-shaped models were already present. Conspecifics’ behaviour, but also their mere presence, seems to be a valuable source of information to decide where to feed. Lizards also showed a strong attraction to conspecifics, even in the absence of food. Maybe the pre- sence of a group is interpreted as an indirect cue for the presence of food. The group size was not important to females, but males had a significantly higher attraction towards groups with three conspecifics. We discuss some characteristics of P. lilfordi at Aire Island that can explain the development of the observed social foraging, as well as their possible consequences. Keywords Social information Á Foraging behaviour Á Conspecific attraction Á Islands Á Podarcis lilfordi Introduction Solitary foragers usually have to sample the environment by themselves, obtaining personal information. Neverthe- less, conspecifics can provide social information (Valone and Templeton 2002), either signals or inadvertent social information (ISI, Danchin et al. 2004). Signals are evolved behavioural traits elicited with the intention of communi- cating, whereas ISI is inadvertently produced by individ- uals engaged in some activity (Maynard-Smith and Harper 2003, p. 3). Some authors divide ISI into social cues and public information; the former would give discrete infor- mation about the presence or the absence of some resource or feature, while public information (Valone 1989) pro- vides graded and continuous information about the quality of a given resource (Dall et al. 2005; Wagner and Danchin 2010). Thus, every individual undertaking an activity is inadvertently sending information that can be received by other conspecifics. If local population density is high, social information can be shared by several individuals (Fletcher 2006). A conspecific is an excellent integrator of all the envi- ronmental variables (Kiester 1979). Not only its behaviour can be a source of social information about the patch or resources, but also its mere presence guarantees a minimal quality of that area or resource (Stamps 1987; Valone and Templeton 2002; Danchin et al. 2004). Even more, the presence of a conspecific in a patch where there is usually food is an informative cue even in the absence of food (Giraldeau et al. 2002; Coolen et al. 2005). Attraction to feeding conspecifics has been reported in different social species (Beauchamp et al. 1997; Galef and Giraldeau 2001; Leadbeater and Chittka 2005; Sontag et al. 2006; Arago ´n 2009). In reptiles, Rand et al. (1975) and Kiester (1975) described how Anolis agassizi and Diploglossus A. Pe ´rez-Cembranos (&) Á V. Pe ´rez-Mellado Department of Animal Biology, Universidad de Salamanca, Campus Miguel de Unamuno, s/n., 37007 Salamanca, Spain e-mail: anapercem@usal.es 123 Anim Cogn DOI 10.1007/s10071-014-0831-3