Very short delays prior to escape from potential predators may function efficiently as adaptive risk-assessment periods
W. Cresswell1,5) , S. Butler2) , M.J. Whittingham3) & J.L. Quinn4) (1 Bute Building, School of Biology, University of St. Andrews, St. Andrews, Fife KY16 9TS, UK; 2 Centre for Agri-Environment Research, School of Agriculture, Policy & Development, University of Reading, Reading RG6 6AR, UK; 3 Division of Biology, School of Biology and Psychology, Ridley Building, University of Newcastle, Newcastle-Upon-Tyne NE1 7RU, UK; 4 Edward Grey Institute, Zoology Department, South Parks Road, Oxford OX1 3PS, UK) (Accepted: 13 October 2008)
Summary Periods between predator detection and an escape response (escape delays) by prey upon attack by a predator often arise because animals trade-off the benefits such a delay gives for assessing risk accurately with the costs of not escaping as quickly as possible. We tested whether freezing behaviour (complete immobility in a previously foraging bird) observed in chaffinches before escaping from an approaching potential threat functions as a period of risk-assessment, and whether information on predator identity is gained even when time available is very short. We flew either a model of a sparrowhawk (predator) or a woodpigeon (no threat) at single chaffinches. Escape delays were significantly shorter with the hawk, except when a model first appeared close to the chaffinch. Chaffinches were significantly more vigilant when they resumed feeding after exposure to the sparrowhawk compared to the woodpigeon showing that they were able to distinguish between threats, and this applied even when time available for assessment was short (an average of 0.29 s). Our results show freezing in chaffinches functions as an effective economic risk assessment period, and that threat information is gained even when very short periods of time are available during an attack. Keywords: predation risk, escape response, flight initiation, escape delay, vigilance.
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© Koninklijke Brill NV, Leiden, 2009 DOI:10.1163/156853909X446217
Behaviour 146, 795-813 Also available online - www.brill.nl/beh
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Cresswell, Butler, Whittingham & Quinn
Introduction Prey are frequently attacked by predators with little warning (Cresswell, 1996). Although an immediate escape because of the appearance of a potential predator might seem appropriate, this may not necessarily be the case because responding to non-predators (e.g., Cresswell et al., 2000), or to predators that do not present a risk (e.g., Cooper, 1998), is costly in terms of energy and time lost to foraging (Ydenberg & Dill, 1986). An immediate response to an attack may also be inappropriate because simply fleeing directly away from the predator may be a less effective anti-predation strategy than other behaviours, for example the use of evasive manoeuvres (e.g., Shifferman & Eilam, 2004), crouching (e.g., Cresswell, 1993; Quinn & Cresswell, 2005b) or hiding (e.g., Cresswell, 1994b). Natural selection may, therefore, favour an economic delay (Ydenberg & Dill, 1986) when approached by a potential predator during which the type of risk involved and the optimum action are both determined. This will be countered, however, by selection for such risk-assessment periods to be short because rapid initiation of escape is a primary determinant of capture success (Hilton et al., 1999; Quinn & Cresswell, 2004, 2006). Under conditions where there is very little time for such risk-assessment, such as when a predator hunts by surprise and appears initially very close to the prey, selection will probably favour an immediate escape flight. A crucial consideration for understanding how periods between predator detection and an escape response (hereafter escape delays) function as risk assessment periods generally is how long such escape delays need to be for important information to be gained, within the context of the stresses of an attack. In this paper we explore whether useful information about predator identity can be gained even when a rapidly approaching potential predator (3.6 m/s) first appears very close (
