Lutra 47(2)_Hoffmann et al_2004

Why males incur a greater predation risk than females in juvenile European sousliks (Spermophilus citellus)

Leaving a familiar area is assumed to involve an increased vulnerability to predation, yet rarely are movement patterns and mortality monitored directly. For this reason we examined the locomotor patterns and activity of 41 juvenile European sousliks (Spermophilus citellus) in relation to their individual fates. We investigated whether mortality risk increases with distance from the natal burrow, and we also attempted to distinguish sex-differential locomotor and anti-predator behaviours explaining the female-biased sex ratio among non-juveniles. During three years, weaned juveniles inhabiting a 4 ha plot in a recreation area north of Vienna, Austria, were equipped with radio collars. Nearly 76% of the tagged juveniles were killed by cats or disappeared with unknown fates. Only 5% (two females) permanently departed from their natal area and survived, that is to say, dispersed successfully. Survival of females more than doubled the male percentage and was independent from distance from the natal burrow, whereas most of the surviving males were philopatric. The major finding of this study was that nonsurviving juveniles had moved faster than survivors, with individual speed resulting in sex-differential mortality. Males tended to move faster than females, incurring a greater risk of predation when remote from their natal burrows. Further analyses of behaviour provided evidences that male-biased mortality could arise from sexually different patterns of time allocation to predator avoidance and vigilance. We conclude that among juvenile Spermophilus citellus, males perform an unfavourable trade-off in surface activity allocated to locomotion and vigilance.