Individual variation in vigilance in female eastern grey kangaroos R. J. Dannock A,B , S. P. Blomberg A and A. W. Goldizen A A School of Biological Sciences, University of Queensland, Brisbane, Qld 4072, Australia. B Corresponding author. Email: r.dannock@hotmail.com Abstract. For herbivores, vigilance usually involves a trade-off with foraging, and a further trade-off between antipredator and social vigilance. Thus individual variation in vigilance may result in significant fitness consequences. We used mixed- effects models to document individual variation in vigilance in wild adult female eastern grey kangaroos (Macropus giganteus) in Queensland, Australia. We tested the effects of group size, presence of adult males and wind on vigilance patterns and variation by analysing 399 five-minute samples on 31 individually identified females who were foraging on the periphery of groups. We determined the proportion of time that individuals spent vigilant, and the proportions of vigilance time spent in social versus antipredator vigilance and in low- versus high-intensity vigilance postures. The proportion of time females spent vigilant decreased with increasing group size but was not affected by wind speed or male presence, while the amount of their vigilance time spent in social vigilance was affected by interactions among the variables. After controlling for these effects, 13 females’ vigilance patterns were significantly different from the population mean. Individual variation was also found in vigilance postures used and the effect of male presence. Understanding individual variation in vigilance is important for understanding individuals’ antipredator and social strategies. Additional keywords: antipredator behaviour, behavioural variation, group-size effect, social vigilance. Received 29 November 2012, accepted 12 August 2013, published online 5 September 2013 Introduction Vigilance is usually thought to allow animals to detect predators, and, as a result, be more likely to escape danger (Fitzgibbon 1990; reviewed by Roberts 1996). However, along with predator detection, vigilance also allows animals to monitor conspecifics to gain information about their location and behaviour (social vigilance) (e.g. Berger 1978; Reboreda and Fernandez 1997; Gaynor and Cords 2012). This information gathering allows individuals to make choices that affect foraging efficiency (Valone and Templeton 2002), mate choice (Berger 1978), predation risk (Roberts 1996; Ellard and Byers 2005), and social interactions (Barbosa 2002; Cameron and Du Toit 2005). Given that vigilance patterns usually reflect a trade-off between feeding and safety (Houston et al. 1993; Brown 1999; Verdolin 2006), variation in vigilance patterns among individuals may have important fitness implications. Understanding individual variation in vigilance is important for understanding social and antipredator behaviour; to better understand these behaviours, studies must assess how social and antipredator behaviours interact, and how and why trade-offs between these behaviours and foraging may differ among individuals. In this paper, we show that female eastern grey kangaroos (Macropus giganteus) exhibit considerable differences in their vigilance patterns, and explore the ways that some factors affect those patterns. Individual variation in vigilance has been shown in several species, including spotted hyenas (Crocuta crocuta) (Pangle and Holekamp 2010), white-tailed prairie dogs (Cynomys leucurus) (Hoogland et al. 2013), nutmeg mannikins (Lonchura punctulata) (Rieucau et al. 2010), yellow-bellied marmots (Marmota flaviventris) (Blumstein et al. 2010), bighorn sheep (Ovis canadensis) (Rieucau and Martin 2008) and redshanks (Tringa tetanus) (Couchoux and Cresswell 2012). However, to test for interindividual differences in vigilance that are due to intrinsic differences among animals, it is necessary to understand the range of extrinsic factors that could alter vigilance and to control for these in analyses. For example, environmental factors such as wind can affect vigilance (e.g. brush-tailed rock- wallabies (Petrogale penicillata): Carter and Goldizen 2003; and Columbian ground squirrels (Urocitellus columbianus): Fairbanks and Dobson 2007). High wind speeds have also been shown to result in altered foraging behaviour, presumably due to an increase in perceived predation pressure (Hilton et al. 1999; Yasué et al. 2003). The effect of wind on individual variation in vigilance behaviour has yet to be quantified but may have important fitness consequences if it has a variable effect on individuals’ vigilance–foraging trade-offs. Group size and composition, and an individual’s position in its group, can also affect vigilance. For example, studies of many taxa have found that when group size increases, the level of vigilance displayed by individual animals decreases (reviewed by Elgar 1989; Beauchamp 2003, 2009). Also, a study on Utah prairie dogs (Cynomys parvidens) found that females exhibited higher levels of vigilance during oestrous periods and when the number of males in neighbouring clans increased (Manno 2007). Journal compilation Ó CSIRO 2013 www.publish.csiro.au/journals/ajz CSIRO PUBLISHING Australian Journal of Zoology, 2013, 61, 312–319 http://dx.doi.org/10.1071/ZO12122