Sleeping Site Selection by Urban Marmosets (Callithrix penicillata) Under Conditions of Exceptionally High Predator Density Marina H. L. Duarte & Robert J. Young Received: 20 November 2009 / Accepted: 27 April 2010 / Published online: 27 November 2010 # Springer Science+Business Media, LLC 2010 Abstract Domestic cats are known to kill small mammals and birds, and represent a predatory threat to all small wildlife. We investigated whether a high cat density affects the choice of sleeping sites of urban marmosets (Callithrix penicillata). One group of marmosets and ≥115 domestic cats live in an 18-ha area in the Municipal Park of Belo Horizonte City, Minas Gerais, Brazil. We observed the selection of 105 consecutive sleeping sites by the marmosets between January and April, 2009. We observed predation of 3 juvenile marmosets by domestic cats and a mean of 3.24 attempted predation events per day. The park contains 3777 trees of 275 species, but the marmosets chose only 6 different species —3 palms, 2 eucalyptuses, and 1 fig— and a total of 12 different sleeping trees. Sleeping sites appeared to be chosen to minimize the risk of cat predation. Marmosets slept only in tall trees (mean±SD=22.49 m±5.4) with high first branches (mean above-ground level= 10.36 m±4.7) and smooth or thorny bark. Marmosets reached sleeping trees from adjacent trees, and neither marmosets nor cats climbed into sleeping trees from the ground. These results suggest that domestic cat predation pressure influences the physical characteristics of marmoset sleeping site selection, e.g., height, to reduce predation rate. Keywords Callithrix . Domestic cats . Predation . Sleeping sites . Tree characteristics Introduction Primates select sleeping sites based on various factors, including safety from predators, comfort and hygiene, social opportunities (Anderson 1998), thermoreg- ulation, (Anderson and McGrew 1984), absence of parasites (Kappeler 1998), territoriality and resource availability (Anderson and McGrew 1984), proximity to Int J Primatol (2011) 32:329–334 DOI 10.1007/s10764-010-9468-5 M. H. L. Duarte : R. J. Young (*) Conservation, Ecology and Animal Behaviour Group, Mestrado em Zoologia, Pontifícia Universidade Católica de Minas Gerais, Coração Eucarístico, 30535-610 Belo Horizonte, Minas Gerais, Brasil e-mail: robyoung@pucminas.br