Aspects of the ecology of insectivorous bats (Chiroptera) in temperate deciduous woodlands
Ecological requirements of temperate bat species have been the subject of research in recent years. Remaining native woodlands are believed to be particularly important as foraging sites for bats in Britain. However, little work has been conducted on these habitats. This thesis examines spatial and temporal variations in bat activity in woodlands in relation to a number of factors including prey availability and diversity, weather variables and vegetation density. In this thesis, preference or avoidance of a woodland microhabitat was found to be related to vegetation density of the shrub and canopy. Optimal microhabitats balance the requirements for openness (related to a bat's morphology and echolocation capabilities) and a degree of shelter (necessary for predator avoidance). Nocturnal activity of Pipistrellus pipistrellus in woodlands was investigated and where the woodland was situated in close proximity to a roost, activity was unimodal during pregnancy, bimodal during lactation, and unimodal after weaning. However, in one woodland where no maternity roost was found close-by, nocturnal activity patterns differed. Seasonal bat activity within woodlands was examined in relation to insect availability and climatic factors. Activity was found to be mainly influenced by insect availability. The weather variables regulating insect abundance vary between woodlands and may largely be a function of site characteristics. The range and diversity of available prey taxa rarely affects activity of P. pipistrellus, the most commonly encountered bat in this study. Bat detectors have been used in many habitat and landscape studies (including this one) to estimate bat activity. Until now, no direct association has been made between the number of bat passes and the density of bats present. This issue was investigated using computer simulation models. A nonlinear relationship was found between bat passes and bat density, reducing to an almost linear relationship at the low bat pass numbers typically found in the field.