Animal Behaviour 98 (2014) 185e192 Contents lists available at ScienceDirect Animal Behaviour journal homepage: www.elsevier.com/locate/anbehav Sentinel dwarf mongooses, Helogale parvula, exhibit flexible decision making in relation to predation risk * Julie M. Kern , Andrew N. Radford School of Biological Sciences, University of Bristol, Bristol, U.K. article info To maximize survival, animals should adjust their behaviour flexibly in response to indicators of pre- Article history: dation risk. Predation risk is affected by a range of ecological, social and individual variables, which can Received 26 March 2014 fluctuate over different timescales. In general, current risk levels are known to influence the behaviour of Initial acceptance 8 May 2014 sentinels, individuals that adopt a raised position to scan for danger while groupmates are engaged in Final acceptance 8 October 2014 other activities. However, there has been little consideration of whether decisions made at different Published online stages of a sentinel bout are affected in the same way by perceived predation risk and whether the same MS. number: 14-00260R level of behavioural plasticity is exhibited when making these different decisions. Here we used detailed behavioural observations and a playback experiment to investigate the behavioural choices of dwarf Keywords: mongoose sentinels at three different stages of a bout (before, start, during). Individuals were more likely fl behavioural exibility to begin a bout, and did so sooner, following alarm calls, which are immediate, direct indicators of decision making elevated risk. Sentinels selected an initial height from which to guard depending on factors that tended dwarf mongoose Helogale parvula to vary in the medium term (hours), choosing higher positions in denser habitat and less windy con- risk sensitivity ditions. In contrast, decisions about bout duration were made in relation to short-term (seconds/mi- sentinel nutes) changes in information, with sentinels guarding for longer when an alarm call was given during a bout, and terminating bouts sooner when groupmates moved out of sight. Our results demonstrate that sentinel decisions are influenced by both direct and indirect indicators of likely predation risk and that sentinel behaviour is adjusted flexibly with regard to information presented on various timescales, highlighting the complexity of decision-making processes. © 2014 The Authors. Published on behalf of The Association for the Study of Animal Behaviour by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/ by-nc-nd/3.0/). Animals constantly make decisions about how to balance con- Blumstein, 1992). Assessing the level of behavioural flexibility flicting demands (McFarland, 1977), with the trade-off between exhibited at different times is therefore also important in the foraging and vigilance a classic example (Lima & Dill, 1990). Infor- investigation of decision making. mation is a vital modulator of behaviour, and to facilitate appro- Decision making in relation to predation risk can potentially be priate decision making, animals continually monitor and assess affected by ecological, social and individual variables. Ecological numerous external and internal factors (Dall, Giraldeau, Olsson, conditions such as habitat type (Werner, Gilliam, Hall, & McNamara, & Stephens, 2005; McFarland, 1977; Trimmer et al., Mittlebach, 1983), heterogeneity (Hilton, Ruxton, & Cresswell, 2008). Behavioural flexibility is limited, however, and while ani- 1999; Rodríguez, Andren, & Jansson, 2001) and quality (Sapolsky, mals are expected to behave optimally, they may be constrained 1986), as well as wind speed (Hilton et al., 1999; Hollen et al., from doing so by, for instance, evolved psychological mechanisms 2011), are associated with changes in predator detectability, den- (Fawcett, Hamblin, & Giraldeau, 2013) or the cost of information sity and behaviour. Similarly, predation risk depends on such social acquisition (Dall et al., 2005). Owing to the stochastic nature of the factors as group size (Hamilton, 1971; Radford & Ridley, 2007) and environment and changing circumstances across time, individuals composition, including the presence of young (Pangle & Holekamp, should take into account fluctuating risk, rather than behave as if 2010; Santema & Clutton-Brock, 2013), spatial position in the the relevant threats to survival were constant (Bouskila & foraging group (Radford & Ridley, 2007), and the activity (Pangle & Holekamp, 2010) and vigilance behaviour (Pays, Blomberg, Renaud, Favreau, & Jarman, 2010; Radford, Hollen, & Bell, 2009; ) of com- panions. Risk levels can also differ for individuals of different age, * Correspondence: J. M. Kern, School of Biological Sciences, University of Bristol, sex and body condition (Burger, Safina, & Gochfeld, 2000; Lea & Woodland Road, Bristol BS8 1UG, U.K. Blumstein, 2011; Lima, 1988), while risk perception may depend E-mail address: [email protected] (J. M. Kern). http://dx.doi.org/10.1016/j.anbehav.2014.10.012 0003-3472/© 2014 The Authors. Published on behalf of The Association for the Study of Animal Behaviour by Elsevier Ltd. This is an open access article under the CC BY-NC- ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). 186 J. M. Kern, A. N. Radford / Animal Behaviour 98 (2014) 185e192 on prior experience (Stankowich & Blumstein, 2005) and person- calls which not only signify ‘danger’ but also indicate the type of ality (Dall, Houston, & McNamara, 2004). predator and urgency of the threat (Beynon & Rasa, 1989). Although Decision making requires continuous acquisition of data over most group members take part in sentinel duty, studies have found time (Trimmer et al., 2008). Individuals must simultaneously variation in the investment of individual classes in different pop- consider multiple processes operating at different rates and time- ulations: Rasa (1989) reported subordinate males investing signif- scales (Heath, Gilchrist, & Ydenberg, 2010), and although some icantly more time in sentinel bouts than other group members, decision-making rules may be fixed and unresponsive to variations whereas no such dominance-based difference has been found at in stimuli, optimal decisions can involve complex interactions our study site (Kern, n.d.). among these multiscale processes (Couchoux & Cresswell, 2012; In the current study, we investigated how predation risk affects Heath et al., 2010). For example, sex usually remains constant decisions at three different stages of a sentinel bout (before, start, across an animal's lifetime, with age accumulating slowly over long during): (1) when to become a sentinel; (2) what height above periods. Individuals experience variation in factors such as habitat ground to choose as an initial position; and (3) how long to remain type and weather conditions in the medium term. Simultaneous as a sentinel. As it is difficult to predict exactly when a natural short-term variation arises as a consequence of, for instance, sentinel bout will start, a playback experiment was used for ques- changes in nutritional state or information provided from the tion (1), increasing perceived predation risk through the use of production of alarm calls by groupmates. alarm calls. For questions (2) and (3), we analysed detailed obser- In a number of social species, the foragingevigilance trade-off vational data of natural behaviour and included various ecological has led to the evolution of sentinel systems (Clutton-Brock et al., (e.g. habitat type, wind condition) and social (e.g. presence of pups, 1999; Horrocks & Hunte, 1986; McGowan & Woolfenden, 1989; occurrence of alarm calls) factors, while controlling for individual Rasa, 1989; Ridley & Raihani, 2007; Wright, Berg, de Kort, Khazin, factors such as sex, age and dominance status. A higher predation & Maklakov, 2001a). Sentinels are individuals that adopt a raised risk might be perceived either following direct indicators of a threat position to scan the surroundings and provide information about (e.g. an alarm call) or in certain conditions, such as in denser hab- potential threats to groupmates engaged in other activities itats (Brown, 1988) or on windier days (Hilton et al., 1999). In these (Bednekoff, 1997; Bell, Radford, Rose, Wade, & Ridley, 2009; situations, we predicted that sentinels would start bouts sooner, McGowan & Woolfenden, 1989). Group members can benefit choose higher initial positions and stay on guard for longer. The from the presence of a sentinel in terms of reduced predation risk observational data sets also allowed a consideration of whether the and increased foraging success (Hollen, Bell, & Radford, 2008; same level of behavioural flexibility is exhibited at different deci- Ridley, Raihani, & Bell, 2010). In general, sentinel behaviour is sion stages. Specifically, are decisions made in relation to factors known to be affected by individual factors, such as age, sex, that alter predation risk in the medium term (e.g. changes in dominance rank and nutritional status. For instance, dominant fe- habitat or group size that might occur across the day) or to factors male meerkats, Suricata suricatta, contribute less to sentinel duty that can alter the perception of predation risk in the short term (e.g. than other adults (Clutton-Brock et al., 1999), sentinel effort in alarm calls, group activity), and is the same level of flexibility Arabian babblers, Turdoides squamiceps, is greater for males than exhibited