Introduction

This review has three main aims: to examine the distribution of bat roosts in relation to rivers and other water bodies, to assess the evidence that some bat species forage preferentially along rivers, and to consider what resources are provided by the rivers for the bats. Recent studies on the effects of eutrophication on bats will also be described. The review will be based principally on information obtained in Britain and will include the published and unpublished results obtained by myself and my colleagues on five rivers in Scotland: the Dee, Don, Ythan, Spey and Tay. The conclusions of these studies together with those selected from mainland Europe and North America are thought to apply equally to rivers in England and Wales or point to the need for similar research in these countries.

Fourteen species of vespertilionid bats breed in the UK and nine are referred to in this review (Table 5.1).

Are bat roosts concentrated in river valleys?

Roosts in buildings

Over the last 20 years, data have been collected of the locations of bat roosts in north–east Scotland (ca. 57 °N), where four bat species commonly occur (Speakman et al, 1991). The pipistrelle is the commonest species and accounted for 147 of 184 bat roosts known in 1989, located close to the Rivers Dee and Don from source to sea (Fig. 5.1). Thirty–four of the roosts were occupied by brown long–eared bats, most of which were concentrated along a well–wooded stretch of the River Dee (Entwistle, 1994).