ANIMAL BEHAVIOUR, 2003, 65, 543–550 doi:10.1006/anbe.2003.2073 Vocal signature recognition of mothers by fur seal pups ISABELLE CHARRIER*†, NICOLAS MATHEVON*‡ & PIERRE JOUVENTIN† *Laboratoire de Biologie Animale, Universite ´ Jean Monnet †CEFE-CNRS UPR 9056, Montpellier ‡NAMC-CNRS UMR 8620, Universite ´ Paris-Sud, France (Received 8 February 2002; initial acceptance 19 March 2002; final acceptance 21 July 2002; MS. number: 7225R) Subantarctic fur seals, Arctocephalus tropicalis, come ashore to breed in dense colonies and lactating females have to alternate foraging trips at sea with periods ashore during which they suckle their pups. The effectiveness of vocal recognition between mothers and pups, has been shown experimentally. To see whether the recognition abilities of females differ from those of their offspring, we investigated how pups recognize their mother’s calls. We used artificially modified signals in playback experiments to determine which acoustic parameters support the recognition process. Pups used both the energy spectrum and the ascending frequency modulation occurring at the beginning of each call. However, they seemed to rely mainly on spectral analyses. The vocal identification process at a perceptual level is therefore asymmetri- cal, as mothers mainly use temporal structures to recognize their pup’s calls.  2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour. In social bird and mammal species, parents and offspring develop the ability to identify each other (Halliday 1983), with mutual fitness benefits (Trivers 1974; McArthur 1982). For parents, offspring recognition prevents mis- directed parental care, limits their expenditure of energy, and ensures their reproductive success. For young ani- mals, recognition of parents is essential to their survival since in most social or colonial species parents feed only their own offspring. There is evidence that parent– offspring recognition is especially important for colonial species, with the degree of recognition (i.e. mutual or unilateral recognition) seeming to vary between species and depending on environmental constraints (Halliday 1983). Some studies have experimentally investigated the sensory modalities supporting individual recognition between parents and offspring, and have shown that identification relies mainly on vocal and/or olfactory signals. Acoustic cues have been well studied in colonial birds (e.g. penguins: Jouventin et al. 1999; Lengagne et al. 2000; Aubin & Jouventin 2002; gulls: Charrier et al. 2001a; swallows: Beecher et al. 1981) but few studies have investigated the fine acoustic processes (information coding/decoding) underlying vocal individual recog- nition in mammals. In this respect, otariids are a good model to explore these mechanisms, because their vocal recognition has been widely observed and experi- mentally demonstrated (Trillmich 1981; Insley 1992, 2000; Charrier et al. 2001b). Otariids breed in large dense colonies. After parturition, females take care of their pups for several months, alter- nating foraging periods at sea, during which pups are left alone in the colony, with periods ashore for the purpose of suckling. Because females do not feed nonoffspring (Boness 1990; Georges et al. 1999), and mother and pup are frequently separated, effective individual recognition between mother and offspring is vital for finding each other among several hundred conspecifics (Riedman 1990). Although this recognition may rely on several sensory modalities, vocal recognition is a key factor as shown by playback experiments in the Galapagos fur seal, Arctocephalus galapagoensis (Trillmich 1981), subantarctic fur seal, Arctocephalus tropicalis (Charrier et al. 2001b, 2002a), and northern fur seal, Callorhinus ursinus (Insley 2000, 2001). In a study on northern fur seals, Insley (2001) showed that the effectiveness of acoustic recognition seems to differ between the female and her pup. In response to playback, pups are more vocally responsive than mothers and sometimes make recognition errors by responding to another female’s calls. In contrast, females respond strongly only to the call of their own pup. From an evolutionary point of view, Correspondence and present address: N. Mathevon, Laboratoire de Biologie Animale, 23 rue Michelon, Universite ´ Jean Monnet, 42023 St Etienne cedex 02, France (email: mathevon@univ-st-etienne.fr). I. Charrier is now at the Department of Psychology, University of Alberta, Edmonton, AB T6G 2E9, Canada. P. Jouventin is at CEFE CNRS UPR 9056, 1919, route de Mende, 34293 Montpellier cedex 5, France. 0003–3472/02/$30.00/0  2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour. 543