Generating, collating and using scientific evidence is key to effective conservation. We illustrate this with examples from medicine and conservation, and in more depth with an example from our own studies, in which we assess the methods (overpasses and underpasses) used to reduce habitat fragmentation and mortality of bats caused by roads. Evidence is defined as the results of quantitative tests of interventions that directly address conservation effectiveness against clearly stated goals. The results show that methods used in the past were rarely tested quantitatively and when tested were rarely effective. We discuss why it can be difficult to get scientific evidence accepted and used routinely in conservation policy and practice. Finally, we discuss how evidence gathering and use can be improved in mitigation projects.

OUTLINE

Despite their small size (2–1000 g), bats have life-cycles comparable to those of much larger mammals, characterized by longevity, low fecundity and substantial parental care (Barclay & Harder, 2003). They also have very diverse life-cycles, with considerable variation in social systems and mating strategies (Altringham, 1996; McCracken & Wilkinson, 2000). There are currently believed to be almost 1100 species in 18 families, dominated by 5 very large families: Vespertilionidae, Rhinolophidae, Molossidae, Phyllostomidae and Pteropodidae (Koopman, 1993). Most species have not been studied, but enough is known about a small but varied minority to begin to understand the significance of the different social structures seen in bats.

Although a common feature in many mammals and often seen in sexually segregated species, marked sexual dimorphism in bats is rare. Female microbats are typically a little larger than males, but the differences are frequently only statistically significant with large sample sizes. One exception is Ametrida centurio, in which the females are markedly larger than the males (Peterson, 1965). The few instances of marked dimorphism are usually adaptations for sexual signalling, such as the enlarged nasal cavities of male hammer-headed bats, Hypsignathus monstrosus, and the erectile and scented hairs of the crested free-tailed bat, Chaerephon chapini (Altringham & Fenton, 2003).

So why do bats segregate by sex? Sexual segregation has been given relatively little attention in bats despite their diversity, their tendency to form large social units and indeed their tendency to segregate.

INTRODUCTION

An answer to the question posed by this paper is still some way in the future. However, recent investigations which draw on both in vivo studies of swimming fish and in vitro experiments on isolated muscle fibres, are shedding some light on the problem. To understand the functional role of myotomal muscle, we need to know the conditions under which it is operating in vivo, and its mechanical performance under these conditions.