Vocal Repertoire of Captive Capybara (Hydrochoerus hydrochaeris): Structure, Context and Function Kamila S. Barros*, Rosana S. Tokumaru , Janine P. Pedroza* & Selene S. C. Nogueira* * Laborato ´ rio de Etologia Aplicada, Universidade Estadual de Santa Cruz, Ilhe ´ us, BA, Brazil  Departamento de Psicologia Social e do Desenvolvimento, Universidade Federal do Espı´rito Santo, Vito ´ ria, ES, Brazil Introduction The capybara is the largest caviomorph rodent in the world, distributed from Panama to northern Argentina (Ojasti 1973; Mones & Ojasti 1986; Em- mons 1990). The species lives in cohesive groups ranging from 10 to 25 adults of both sexes (Azca- rate 1980). The capybara group shows a complex social behavior with territoriality and social domi- nance hierarchy (Ojasti 1973; Macdonald 1981; Shaller & Crawshaw 1981; Herrera & Macdonald 1987, 1993). The social group is very cohesive and does not tolerate individuals from other groups (Ya ´- ber & Herrera 1994; Nogueira et al. 1999). The sub- ordinate male is often vigilant against conspecific intruders or any other potential danger (Ya ´ber & Herrera 1994). Some naturalistic researchers, working with this species, have already noticed that capybaras often emit loud and low volume sounds while interacting (Ojasti 1973; Azcarate 1980; Lord 1994). Lord (1994) reported calls that sound like barks, whistles and chuckles. According to this author, barks were recorded during potential predator presence. Whis- tles were associated to infants calling their mother and chuckles to individuals traveling together. At night, capybaras were heard emitting constant low vocalizations described as clucking and clicking noises (Lord 1991). The same vocalizations were also reported by other authors (Ojasti 1973; Azcarate 1980; Ya ´ber & Herrera 1994; Murphey et al. 1998). However, to date these vocalizations have not been described structurally. Their acoustic structure is unknown, which prevents the correct discrimination among the various types of vocalizations and, conse- quently, further advances in studies on vocal com- munication of this species are needed. The knowledge about vocal repertoires allows inferences about phylogenetic differences (Range & Fischer 2004; Gonzaga et al. 2007), behavioral functions (Lord et al. 2009), ontogenetic aspects (Stoeger- Horwath et al. 2007), leads to better comprehension Correspondence Selene S. C. Nogueira, Laborato ´ rio de Etologia Aplicada, Universidade Estadual de Santa Cruz, Rodovia Ilhe ´ us – Itabuna, km 16, 45662-000, Ilhe ´ us, BA, Brazil. E-mail: selene@uesc.br Received: March 24, 2010 Initial acceptance: July 14, 2010 Final acceptance: October 7, 2010 (D. Zeh) doi: 10.1111/j.1439-0310.2010.01853.x Abstract In this work we describe the structure, behavioral context and function- ality of the vocal repertoire of capybaras, a social Caviomorph rodent. Additionally, since territoriality is present in this species, we hypothesize the occurrence of vocal differences among social groups. We analyzed a total of 2069 calls emitted by 28 animals from three different social groups. The capybara’s repertoire is comprised by seven call types (whis- tle, cry, whine, squeal, bark, click and tooth-chattering). The vocaliza- tions were functionally categorized as contact, alarm, distress and agonistic calls considering their behavioral contexts. The click calls emit- ted by the adults of the three captive capybara groups were significantly different, confirming our hypothesis of social groups’ vocal differences. The richness of interactions mediated by vocalization in capybaras sug- gests that the species’ communication is an important mechanism to regulate social encounters and to alert members of the group about environmental cues. Ethology Ethology 117 (2011) 83–93 ª 2010 Blackwell Verlag GmbH 83