Spatial and sexual segregation of Daubenton's bats in Wharfedale: a behavioural and genetic approach

Daubenton's bats are small (~8g) insectivorous bats which feed almost exclusively over water.

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Daubenton's bats have been studied in Wharfedale, in the Yorkshire Dales, for several years and have been shown to exhibit a pattern of sexual and spatial (habitat) segregation (Altringham and Waters, in prep).

Only males roost and feed at higher elevations, where insect densities are lower and the foraging conditions are more difficult, while females and a few adult males occupy the lower parts of the river, based in nursery roosts (Altringham and Waters, in prep). Similar patterns of habitat segregation may be common in many Daubenton's bats (Myotis daubentonii) populations and other bat species (Leuzinger and Brossard, 1994; Barclay, 1991).

Differences between sexes in habitat use are widespread among sexually dimorphic mammals, but have only been closely studied in ungulates (cloven hooved mammals) (Clutton-Brock et al., 1987). It was suggested that males might be forced into marginal habitats because their greater size and foraging requirements render them inferior to females in indirect competition for the best foraging sites. Bats show only slight sexual dimorphism and therefore represent a valuable contrast to ungulates in the study of social segregation.

Two alternative hypotheses for the underlying mechanisms of segregation in M. daubentonii in Wharfedale will be investigated:

Segregation is the result of `indirect competition´ with reproductive females and/or lower dale males, as proposed for ungulates.
Alternatively, the upper dale is optimal habitat for males and segregation is the result of differing foraging strategies used by the two sexes. Males can use torpor on a daily basis to reduce energetic costs, allowing them to exploit more patchy insect densities. Constraints imposed on females by gestation and lactation restrict their ability to use torpor.

These hypotheses are being addressed with ongoing studies of habitat structure, foraging efficiency, prey abundance, bat condition and bat interactions. The consequences of segregation on the relative mating success of the two different groups of males (upper and lower dale) will be determined using microsatellite marker analysis.

These methods will be used to determine which of the proposed hypotheses explain the spatial and sexual segregation exhibited by M. daubentonii.

References

Barclay, R.M.R. (1991) J. Anim. Ecol. 60, 165-178.

Clutton-Brock, T.H., Iason, G.R. and Guiness, F.E. (1987) J. Zool. Lond. 211, 275-289.

Leuzinger, Y. and Brossard, C. (1994) Anim. Behav. 53, 991-999.

Background references

Altringham, J.D. (1996) Bats: Biology and Behaviour (264pp) Oxford, Oxford University Press.. Reprinted in paperback in 1998, 1999. Japanese translation 1998.

Park, K.J, Masters, E. and Altringham, J.D. (1998) Social structure and mating patterns of three sympatric species of vesper bats. J. Zool. Lond 244, 379-389.

Warren, R.D., Waters, D.A., Altringham, J.D., and Bullock, D.J. (2000) The distribution of Daubenton´s bats Myotis daubentonii and pipistrelles Pipistrellus pipistrellus in relation to small-scale features of riparian habitat. Biol.Cons. 92, 85-91.