Habitat use varies with reproductive state in noctule bats (Nyctalus noctula): Implications for conservation

Many temperate zone bat species form colonies during the highly synchronised summer breeding period allowing differences in foraging behaviour to be compared between females in different reproductive states. Such comparisons may clarify mechanisms of population regulation. Individual female (n = 20) noctule bats (Nyctalus noctula) from the same colony, but in different reproductive states (lactating or non-lactating), were radio-tracked and their use of foraging space, in relation to available habitat types, assessed and compared. Habitat preference was determined using compositional analysis on two levels: overall preference within the minimum convex polygon (MCP) used by the colony (total area 62.75 km(2)) and overall preference within individual bat MCPs (mean area 8.2 km(2)). A further comparison of relative habitat use, between lactating and non-lactating bats, demonstrated state-dependent differences in use and identified habitats important for foraging in reproducing bats. Broadleaved woodland and pasture were the highest ranked foraging habitats consistently preferred by noctule bats across both levels. Although there was little difference in foraging activity (e.g. nightly duration, median 115 min) or maximum distances travelled to foraging grounds (mean 4.23 km), non-lactating bats used less preferred marginal habitats (arable land and moorland) significantly more than lactating bats. The observed spatial partitioning is discussed in relation to density dependence and the conservation implications of changing land use for bat populations.