How does the morphology of gleaning bats constrain their locomotor performance?

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Abstract

Abstract for the Thesis “How does the morphology of gleaning bats constrain their locomotor performance?” submitted by James Gardiner for the degree of PhD in the Faculty of Life Sciences at the University of Manchester in September 2011.Bats are one of the most numerous and diverse orders of mammals. This diversity is reflected in the wide range of bat morphologies. The relationship between bat foraging behaviours, flight styles and wing shapes has been well studied. Little research, however, has focused on other features of bat morphology, such as ear and tail membrane size, and how variations in these affect a bat’s locomotion. Indeed, knowledge on this topic has at best been speculative. In this thesis, I provide insight into the trade-offs and relationships that exist between less studied aspects of bat morphology, and their foraging and locomotion, with focus on the group of bats referred to as gleaners. In this thesis I use a model bat in wind tunnel tests to demonstrate that the long ears of some bat species have profound implications for their aerodynamic performance, and their energetics. A trade-off, however, is likely to exist, since the long ears provide a foraging benefit, which may balance the additional flight cost of the large ears. Additionally, bats may be able to minimise the flight cost of their ears through appropriate ear positioning. Using data collected from museum specimens I also demonstrate that other features of bat morphology, particularly the tail membrane, are good indicators of foraging strategy. Gleaning bats are identified as the group with the largest ears, whilst commuting bats have the shortest tail membranes. The energetic implications of these variations in morphology were then investigated using a theoretical model. The theoretical model suggested that tail morphology, as well as ear morphology, was likely to have a profound effect on flight performance in bats In contrast to bird tails the aerodynamic function of bat tail membranes is not well understood. Accordingly, I investigated bat tail membrane aerodynamics empirically using a model suspended in a wind-tunnel and from this was able to present the first evidence that bat tail membranes fulfil an important flight control function. Although bats primarily fly, certain species, such as the gleaning bats, spend a significant proportion of their foraging time on or near the ground and vegetation, landing to capture prey. Several gleaning species are also documented as frequently jumping from the ground back into flight. Research, however, on bat jumping had previously concentrated on the unusual vampire bats. I, therefore, present further data on bat jump performance and show that no ecological trend is present, with body mass being the best indicator of performance. No correlation between foraging habit and take-off performance suggested that flight so dominates bat morphology and locomotor performance that other modes of locomotion tend to be derivative.The findings of the thesis presented here, provide important insights into the relationships that exist between gleaning bat morphology, locomotor performance and foraging strategy. Areas for future research are also identified.

Keyword(s)

bat; morphology

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