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Published by Pelagic Publishing

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PO Box 725, Exeter, EX1 9QU, United Kingdom

British Bat Calls

A guide to species identification

ISBN 978-1-907807-25-1 (Pbk)

ISBN 978-1-907807-26-8 (eBook)

All rights reserved. No part of this document may be produced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without prior permission from the publisher.

While every effort has been made in the preparation of this book to ensure the accuracy of the information presented, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Pelagic Publishing, its agents and distributors will be held liable for any damage or loss caused or alleged to be caused directly or indirectly by this book.

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library.

Cover image © NHPA/Melvin Grey

Greater horseshoe bat, Rhinolophus ferrumequinum in flight

Typeset and eBook by Graphicraft Limited, Hong Kong

Contents

Acknowledgements

Preface

1. Introduction

2. Bats and sound

2.1 Properties of sound

2.2 Signal acquisition

2.3 Representing and describing sound

2.4 How bats use sound

3. Equipment

3.1 Bat detectors

3.2 Recording sound

4. Call analysis

4.1 Sound analysis software

4.2 Automatic recognition software

4.3 Using sound analysis software

4.4 Measuring call parameters

4.5 AnalookW

4.6 Common analysis problems

5. Species echolocation guide

6. Species identification

Bibliography

Index

About the author

Jon Russ first became interested in bats in 1994 while completing undergraduate research into pipistrelle social calls as part of an honours degree in zoology at the University of Aberdeen. This led to a PhD at Queen’s University Belfast investigating the community composition, habitat associations and echolocation calls of Northern Ireland’s bats. Since then he has been involved in a wide variety of bat-related projects which have taken him from the freezing mists of north-east Scotland and the fine soft nights of Ireland to the humid rainforests of Madagascar, Thailand and Burma. Jon is the Director of Ridgeway Ecology, a specialist bat consultancy, and has worked for a number of years for the Bat Conservation Trust coordinating the iBats project in the UK and Eastern Europe. After nearly 20 years involvement in bat research and conservation he continues to be fascinated by these remarkable mammals.

About the contributors

Kate Barlow works for the Bat Conservation Trust (BCT) as the Development Manager for the National Bat Monitoring Programme. She has a long-term interest in bats, sparked by catching exotic species during summer expeditions to South America as an undergraduate. Kate has held a bat licence in the UK since 1993, worked as a professional bat consultant before joining BCT and obtained a PhD in bat ecology in 1997 through her research on ecological differences between what are now two separate species of pipistrelle.

Philip Briggs works for the Bat Conservation Trust as the Projects Manager for the National Bat Monitoring Programme. He has a lifelong interest in wildlife, has been involved in bat conservation since 2001 and holds a bat licence. Philip has a particular interest in bat echolocation and delivers training in species identification using bat detectors and sound analysis.

Dr Sandie Sowler is a bat specialist and ecological consultancy trainer, specialising in delivering training in bat-related subjects to the profession, including the use of bat detectors, particularly Anabat and Analook. She has been involved with bats and in bat research since 1969, has a PhD in bat ecology, has had a UK bat licence since 1985 and has worked as a professional ecological consultant, specialising in bats and developments since 1995. Sandie currently delivers Anabat training courses in several European countries and also in Southern Africa.

This book was completed in collaboration with the Bat Conservation Trust (BCT) and some sections draw on existing BCT training material. The Bat Conservation Trust was formed in 1991 and is the only UK-wide organisation solely devoted to the conservation of bats and their habitats. BCT’s vision is a world where bats and people thrive together in harmony and is working towards a future where our bat populations are viable and actively supported and enjoyed by people across the UK. BCT is a registered charity with nearly 5,000 members and a team of over 30 staff including scientists, biodiversity officers, database managers and specialists in training, outreach and education, volunteer engage-ment, fund raising, media and membership. It has particular expertise in bat monitoring and delivery of projects to conserve bats. Through the hard work and dedication of our volunteer network, BCT runs the National Bat Monitoring Programme, which comprises a number of national annual surveys to monitor the status of many of our bat species across a range of habitats. As part of this programme we provide training and information for volunteers on different types of bat detectors and recording devices (on which some of the information in this book is based), and helpful information about bat echolocation. Visit www.bats.org.uk to find out more.

Acknowledgements

I am hugely indebted to Nigel Massen of Pelagic Publishing who resurrected this project and to Kate Barlow, Philip Briggs and Sandie Sowler who contributed greatly to the content. Specifically, Kate and Philip wrote the majority of Chapters 3 and 4 (Equipment and Call Analysis), refined Chapters 2 and 6 (Bats and Sound; Species Identification) and commented on the final draft, while Sandie added the frequency division sections to Chapter 6 (Species Identification). Sandie also provided the text on which the zero crossing information in Chapter 4 is based. Without their input this book would not have been completed. Parts of Chapters 3 and 4 draw on BCT resources written by Jules Agate and Colin Catto.

Many thanks to Danilo Russo and Jules Agate for commenting on earlier versions of the book and to Hazel Gregory and Steve Russ for providing much needed proofreading. Steve additionally helped refine the Introduction and Preface.

I am grateful to Tom McOwat for producing the beautiful illustrations of bat wing shapes, ear shapes and habitats in Table 2.1 and the pipistrelle bat in flight on the title page.

John Altringham generously supplied the time-expanded recording of a feeding buzz of Myotis alcathoe and a copy of two research articles (Jan et al., 2010 and von Helversen et al., 2001) upon which much of the Myotis alcathoe section is based. David Lee and Denise Foster provided a time-expanded recording of the echolocation call of a hand-released Myotis alcathoe and Alex Lefevre provided a recording of M. alcathoe from Hermeton-sur-Meuse in the south of Belgium. David also kindly provided a recording of a social call of Nyctalus noctula. Jules Agate provided a time-expanded recording of the echolocation calls of Myotis bechsteini. Erika Dahlberg provided the time-expanded recordings of a Plecotus auritus social call, the echolocation and social calls of Plecotus austriacus, as well as a copy of her BSc Hons thesis (Dahlberg, 2004) containing measured parameters of the calls of these two species. Arjan Boonman supplied time-expanded social calls of Myotis nattereri and Myotis daubentonii swarming in a cave. Mathieu Lundy provided a time-expanded M. nattereri echolocation and social call and Austin Hopkirk generously provided a time-expanded recording of M. daubentonii leaving a roost. A number of people generously allowed us to use their Anabat recordings: David Hunter provided lesser horseshoe bat social calls; David Woolley allowed use of his greater horseshoe bat social calls, whiskered bat distress calls and Leisler’s bat echolocation calls; Stephen Davison provided recordings of the social calls of whiskered bats emerging from a roost; Claire Snowball provided noctule social calls; David Fee provided brown long-eared bat echolocation and social calls; Orly Razgour provided grey long-eared bat echolocation and social calls; and Margaret Clarke kindly provided a barbastelle social call.

The following people also assisted during the protracted process of creating this book: Arjan Boonman, Darren Bradley, Colin Catto, Thierry Disca, Andrew Heath, Marc Holderied, Austin Hopkirk, Gareth Jones, Kate Jones, Herman Limpens, Iain Mackie, Kate McAney, Andrew McLeish, Katie Parsons, Lars Pettersson, Dave Russ, Mark Smyth, Jackie Underhill and Nancy Vaughan.

I would particularly like to thank Paul Racey who not only inspired my interest in bats but also enabled me to pursue a career that has been so rewarding.

The software programs Batsound v3.31 (Pettersson Elektronik AB, Uppsala, Sweden), Avisoft SASLab v4.6 and AnalookW v3.3f (Chris Corben) were used to construct the sonograms, oscillograms and power spectra displayed in this book. The majority of the calls were recorded using a Pettersson D-980 bat detector (Pettersson Elektronik AB, Uppsala, Sweden).

The author welcomes comments regarding this book and would be grateful for any recordings of bat vocalisations that could be used in future editions (email: batcalls@ridgewayecology.co.uk).

I would like to thank Eimear for all her love and support during the writing of this book, which is dedicated to Ellen, our beautiful daughter.

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Preface

While working on a PhD in the late 1990s, investigating the community composition, habitat associations and ultrasound of Northern Ireland’s bats, I compiled a series of species notes to assist me with identification of bats by their echolocation calls heard or recorded in the field. I soon realised that this could be of use to other bat enthusiasts. Combining these notes with handouts for bat detector workshops, it gradually metamorphosed into a beginners guide to bat identification using heterodyne and time expansion detectors. Those species also occurring in Britain were added in response to demand and sections on how bats use sound and the recording and analysis of sound were included in order to support the identification guide. In 1999 The Bats of Britain and Ireland: Echolocation Calls, Sound Analysis, and Species Identification was published by Alana Books.

Over the following years I gradually accumulated new recordings of echolocation calls and social calls of British bats, not only those I had recorded myself but also those that had been kindly sent to me by other bat enthusiasts. It seemed like a good idea to make these available to others through the publication of a follow-up to that initial guide. The rapid increase in the number of people with an interest in bats, ranging from voluntary bat group workers and researchers to the growing number of bat consultants, persuaded me that such an update would be useful to many in the field of bat conservation. With the invaluable input of Kate Barlow and Philip Briggs of the Bat Conservation Trust and Sandie Sowler, an expert on identification of bat calls using the Anabat system, the scope of the book grew to include updated sections on bats and sound, a much improved and comprehensive section on species identification, and new chapters on equipment and call analysis. I hope it will be useful to amateurs and professionals alike.

1 Introduction

In 1793, Lazzaro Spallanzani, an Italian Catholic priest, biologist and physiologist, demonstrated that bats were able to avoid obstacles without the aid of vision. He stretched thin wires with small bells attached across a completely darkened room and observed that bats were able to fully navigate between them without causing the bells to ring. Blinding the bats also did not impair their ability to manoeuvre around them. Meanwhile, a Swiss zoologist, Charles Jurine, revealed that blocking one of the ears of a bat spoiled its navigating abilities, a finding that Spallanzani then pursued. A series of experiments which involved blocking the ears or gluing the muzzle closed led him to conclude that while bats did not have much use for their eyes, any interference with their ears that adversely affected hearing was disastrous, resulting in them colliding with objects they could usually avoid and being unable to forage for prey. He concluded that ‘The ear of the bat serves more efficiently [than the eye] for seeing, or at least for measuring distance’. At the time, Spallanzani’s findings were met by his fellow scientists with ridicule and scepticism as bats were believed incapable of producing any sound and therefore such results defied logic.

Nearly 150 years after Spallanzani’s work, Donald R. Griffin, while an undergraduate at Harvard University in the 1930s, took an interest in Spallanzani’s ‘bat problem’. New advances in technology allowed him to use a ‘sonic receiver’, designed and built by Harvard physics professor George Washington Pierce. This device captured high-frequency sounds that were beyond the range of human hearing, and reduced the pitch to an audible level. For the first time, it became apparent that bats emit short, loud, ultrasonic clicking sounds. Along with a fellow student, Robert Galambos, who was an expert in auditory physiology, Griffin designed a set of further experiments which showed that bats were avoiding obstacles by hearing the echoes of their ultrasonic cries. Further experimentation revealed that bats were able to adjust the structure of their calls for prey search and capture and for collision avoidance. Griffin named this acoustic orienting behaviour ‘echolocation’.

A bat’s echolocation system is highly sophisticated. By emitting short high-frequency pulses of sound from their mouths or noses, bats are able to use the information contained within the echoes returned from a solid object to construct a ‘sound picture’ of their environment. Not only are they able to identify the size, position and speed of objects within three-dimensional space, they are also able to differentiate forms and surface textures. However, as there is no single signal form that is optimal for all purposes, bats have evolved a large number of signal types. This diversity of echolocation signals is likely to reflect adaptations to the wide range of ecological niches occupied by different bat species. For example, in the UK, the noctule, which largely forages high over parkland, pasture and woodland in an uncluttered environment, tends to produce extremely loud low-frequency calls of relatively long duration, narrow bandwidth and low repetition rate. Conversely, Bechstein’s bat, which often forages very close to or within woodland vegetation in a very cluttered environment, usually produces relatively quiet, very broadband calls of short duration with a high repetition rate. Thus the calls of different bat species are shaped by the habitats in which they usually forage and the resulting different call types can often be used to separate species in the field. However, echolocation call shape is not fixed for a species and shows a certain degree of plasticity depending on the habitat within which an individual is currently located. In addition, although habitat is a significant factor determining the ‘shape’ of bat echolocation calls, they may also vary with sex, age and body size, geographic location and presence of conspecifics. Finally, species that occupy similar niches may use similar echolocation call types and there is often significant overlap in calls between species. An understanding of these different levels of variation both within and between individuals and species is essential to the successful use of echolocation calls for bat species identification.

Social calls produced by bats are often more structurally complex than echolocation calls used for orientation. Social calls are used to communicate with other bats, and for many species they consist of a wide variety of trills and harmonics, comparable in many respects to bird song. It is often surprising to discover just how musical these creatures sound. Social calls may have a number of functions. Some are used to defend patches of insects against other bats or to sustain territorial boundaries. Others function in attracting a mate or, in the case of distress calls, to initiate a mobbing response. Perhaps the most astounding are the isolation calls emitted by young bats, which allow their mothers to identify them. At Bracken Cave in Texas, for example, millions of Mexican free-tailed bats (Tadarida brasilensis) cluster in a large maternity colony. After the mothers have given birth the walls of the cave are literally covered with young bats packed tightly together. Each of these young bats produces an individually specific call that is in some way different from that of all the other young bats. These variations enable a returning mother to distinguish her own offspring amongst all the others.

Since Griffin’s discovery, a number of techniques have been developed to allow us to listen to the ultrasonic vocalisations of bats. These range from relatively cheap ‘heterodyne’ detectors which convert a narrow range of frequencies into an audible signal in the field to ‘real time’ recording that has become possible through the development of high-speed analogue to digital converters built into or connected to computers or solid-state recorders. These high-tech devices utilise a sufficiently high sample rate to enable the ultrasound to be captured digitally without any subsequent processing and allow later processing and analysis of recordings. More recently, bat enthusiasts and researchers have been taking advantage of the explosion in the availability of smartphones. Currently, these devices can be used as recording devices when connected to a bat detector that converts the ultrasound into the audible range. However, with the very recent development of small inexpensive USB ultrasonic microphones, the possibility of turning a smartphone into a ‘real time’ ultrasound recording device is not far off. Incorporation of classification algorithms (a small number of which are available or under development and which assign these calls to species) into such equipment will one day provide instant identification of bat species in the field in a readily available, cost-effective hand-held device.

Donald Griffin referred to his discovery of echolocation as ‘opening a magic well’ from which scientists have been extracting knowledge ever since. Echolocation provides a window into the lives of bats, giving us access to a previously unknown world. It has been used, for example, to help us identify individuals to species; locate roost sites, find commuting routes and foraging areas; study foraging behaviour; establish species distributions; and monitor annual variations in bat populations. In addition, the study of the social calls of bats has allowed us to investigate the vocabulary of bat communication. Not only can these calls be used to identify species of bat and individuals, some calls can also be used to assess male territoriality and female selection of mates as well as providing a measure of male reproductive success while others can give us an insight into female and young interactions, food competition at foraging sites and levels of distress. However, although a great deal has already been learned about the vocalisations of bats, much still remains to be discovered.

The importance of sound to bats cannot be underestimated. They rely upon sound to locate food, to find their way around in the dark, and to seek out and communicate with other bats. By using ultrasonic detectors to eavesdrop on them we are able to investigate their behaviour in the field without disturbing and endangering these remarkable mammals. In this book, I provide a guide to listening to, recording and analysing the echolocation and social calls of bat species found in the UK. Although we cannot always reliably identify all bat species from their echolocation calls, I have tried to give as much information as possible on how to identify bats from their calls using different types of bat detectors.