Bat Roosts Trees: Guide Identification

Bat Roosts Trees: Guide Identification

by Bat Tree Habitat Key


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This is a guide to finding tree-roosts. It is the result of the collaborative efforts of professional surveyors and amateur naturalists across Europe as part of the Bat Tree Habitat Key project, and represents a combination of firsts:

It is the first time legislation and planning policy have been reviewed and put to practical use to define an analysis framework with clearly identifiable thresholds for action. Yet, despite its efficacy in a professional context, it is also the first time a guide has been produced that is equally effective in achieving its objective for amateurs.

It is the first time such a method has been evidence-supported throughout, with summary reviews of each aspect of the roosting ecology of the individual 14 tree-roosting species, with illustrative photographs and data to which the reader has open access.

It is the first time a repeatable analysis framework has been defined against which the surveyor may compare their results at every stage, from the desk-study, through ground-truthing, survey and analysis, thereby ensuring nothing is overlooked and that every result can be objectively compared. The survey and analysis framework itself is ground-breaking in that it may readily be adapted for any taxa; from moths, through amphibians, reptiles, birds and all other mammals.

Used diligently, these methods will reward disproportionately and imbue the reader with renewed confidence as they quickly progress from beginner to competency. Thus, this book is for everyone who has ever wanted to find a tree-roost, or to safeguard against inadvertently damaging one.

Product Details

ISBN-13: 9781784271619
Publisher: Pelagic Publishing
Publication date: 12/09/2018
Pages: 248
Product dimensions: 6.69(w) x 9.63(h) x 0.71(d)

About the Author

Bat Tree Habitat Key is an entirely altruistic collaborative project, set up by Henry Andrews, that has been running since 2010. The project objective is to provide an identical detailed account of how each bat species exploits trees as roost sites. This is achieved by data review, collection and analysis within a standardised format, as well as the collection of photographic accounts, which may be contributed by anyone, and are made publicly available for everyone.

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In this chapter

Introduction Curiosity and necessity
Pre-existing published advice Its effective application
Motivation A cursory review of legislation
Objective Policy and the threshold of "reasonable likelihood" ('more-likely-than-not')
Proportionality Balance; ensuring the ends justify the means

1.1 Introduction

There is more than one reason for reading this book, but all reasons can be divided into two broad camps:

» Curiosity.

» Necessity.

If you have opened this book because you are curious, then you know your level of motivation and what you hope to gain from the exercise.

If you have opened this book out of necessity, it is possible you do not want to read it and may not be motivated at all.

The irony is that those of you reading out of curiosity may read this chapter or not as you choose, but those of you reading out of necessity, even if you have little or no motivation, must read this chapter.

Let there be no misunderstanding: every tree is contentious and a woodland is an anvil waiting to fall Looney-Tunes-style upon the career of the unwary.

There is always public opposition to any operation that may fell trees. If you are assessing an area of woodland in support of a development proposal, you may well find yourself in the local paper. If you are assessing Ancient Semi-Natural Woodland in support of a development proposal, it is well within the bounds of probability that you will end up facing a Public Inquiry and national infamy, so you would be wise to ensure your appraisal is robust, because the opposition may bring in a hired-gun to try and shoot it full of holes.

In the recent past it has been common practice for appraisals of wooded habitat to defer to published guidance, in an (entirely understandable) attempt to guard against the possibility that a client might fall foul of conservation legislation, and to avoid any challenge from a third-party (such as a Local Authority Ecologist).

1.2 Pre-existing published advice

At the time of writing (2018), there are currently two publications that deal with roost surveys in wooded habitat:

» British Standards Institute 2015. BS 8956 – Surveying for bats in trees and woodland. BSI London; and

» Collins J. (ed.) 2016. Bat Surveys for Professional Ecologists – Good Practice Guidelines. London: Bat Conservation Trust.

Both include sensible advice and both have an entirely honourable foundation. Nevertheless, this book will not refer to either of these guidance documents again following this chapter. The reason for this is that routine deference to published guidance (without having reviewed the differences between each individual species, and thereon tailored the actions advocated to the most effective equipment, method, timing and effort in the context of a specific project) dulls the edge of the surveyor. To a certain extent, it also denies the surveyor the satisfaction of designing the survey, and ultimately the joy of performing it.

Thankfully, the authors of both guidance texts were sufficiently experienced as to anticipate this, and both allow for creative input in the design of appraisals.

The British Standard opens with this statement:

"As a guide, this British Standard takes the form of guidance and recommendations. It should not be quoted as if it were a specification or a code of practice and claims of compliance cannot be made to it."

This is also the spirit of text within subsection 1.1.3 of Bat Conservation Trust's Good Practice Guidelines, which states:

"The guidelines should be interpreted and adapted on a case-by-case basis according to site-specific factors and the professional judgement of an experienced ecologist. Where examples are used in the guidelines they are descriptive rather than prescriptive."


"It is accepted that departures from the guidelines (e.g. either increasing or decreasing the number of surveys carried out or using alternative methods) are often appropriate. However, in this scenario an ecologist should provide documentary evidence of (a) their expertise in making this judgement and (b) the ecological rationale behind the judgement."

In this context 'descriptive rather than prescriptive' might be taken to mean that the examples are not rules that must be enforced. Nevertheless, although the guidance is not a book of rules, any deviation should be supported by tangible evidence that demonstrates unequivocally the following criteria:

» The circumstances warranted the deviation.

» The method and intensity employed can be proven to be appropriate for the circumstances.

In essence, the requirement is for evidence-supported action, which is both reasonable and sensible. An approach that has been found to satisfy this requirement has been to design the survey and, when the team is satisfied that the design will collect robust data that is justifiably necessary and that can be meaningfully interpreted within a repeatable framework, to compare their design with BS8956 and the guidance produced by Collins (2016) to see how far their design deviates, and why. This ensures the recommendations are supported by evidence to which the reader of any subsequent report will have access, and provides the reader with sufficient information to allow them to perform an independent critical appraisal of the rationale adopted. The process is broadly this:

Step 1 Review the legislation, planning policy and case-law, and any pertinent consultation in order to define an interpretation threshold against which data may be compared.

Step 2 Collate the existing scientific evidence and ensure copies of any texts that were referred to in the survey design are available for third-party review.

Step 3 Gather and collate pre-existing intelligence relating to the site.

Step 4 Review the existing intelligence and conduct a proportionality test to decide whether surveillance is appropriate.

Step 5 If surveillance is appropriate, review the methods available and chose the most effective suite to suit the context of the site and operation proposed (i.e development, management action, etc.).

Step 6 Identify constraints; acknowledge them and mitigate where possible.

Step 7 Define the analysis framework and identify the predicted outcome.

Step 8 Perform the survey.

Step 9 Interpret the results within a repeatable framework.

Step 10 Acknowledge any failings and, where possible, make suggestions as to how these might be overcome.

Step 11 Actively encourage critical attack in order that any unidentified failings that may potentially exist are found and given due attention.

1.3 Motivation

1.3.1 The law

For most tree-care professionals, ecological surveyors and consultants, our motivation to search for bat roosts is founded in the law, and our desire to remain on the right side of it. There are currently two mechanisms that spur our action:

» The Wildlife & Countryside Act 1981 (& as amended).

» The Conservation of Habitats and Species Regulations 2017.

The two pieces of legislation are set out below.

Wildlife & Countryside Act 1981

All bat species are listed under Schedule 5 of the Wildlife & Countryside Act 1981 and receive legal protection under Part 1, section 9, sub-section (4)(b) and (c) which states:

"Subject to the provisions of this Part, a person is guilty of an offence if intentionally or recklessly —

(a) he disturbs any such animal while it is occupying a structure or place which it uses for shelter or protection; or

(b) he obstructs access to any structure or place which any such animal uses for shelter or protection."

Conservation of Habitats and Species Regulations 2017

All bat species are listed under Schedule 2 of the Conservation of Habitats and Species Regulations 2017.

Part 3, regulation 41, paragraph (1) of the Conservation of Habitats and Species Regulations 2017 states:

"A person who —

(a) deliberately captures, injures or kills any wild animal of a European protected species,

(b) deliberately disturbs wild animals of any such species,

(c) deliberately takes or destroys the eggs of such an animal, or

(d) damages or destroys a breeding site or resting place of such an animal, is guilty of an offence."

Note: The offence of damaging or destroying a breeding site or resting place does not include the word 'deliberately', but is an absolute offence that does not require any fault elements to be proved to establish guilt.

Part 3, regulation 41, paragraph (2) states that disturbance of animals includes any disturbance which is likely:

"(a)to impair their ability —

(i) to survive, to breed or reproduce, or to rear or nurture their young, or

(ii) in the case of animals of a hibernating or migratory species, to hibernate or migrate; or

(b) to affect significantly the local distribution or abundance of the species to which they belong."

1.4 Objective

Although the motivation for performing a survey may have a legislative foundation, the discipline is not an exact science – the law cannot therefore be easily used to define a robust objective, and without a clear objective the interpretation of surveillance results will be handicapped. To explain: the motivation is why the appraisal is performed, and the objective is what the appraisal aims to achieve.

The fundamental difference between good and bad appraisals is the ability to define the objective.

A good objective is straightforward and single-minded. It may only comprise a component part of an overall wider campaign, but it is palpable; you can see it clearly and hold it in your mind. A good objective ensures the appraisal is not distracted or side-tracked because it knows its weight, worth, and why it is needed, it can therefore justify its own existence and stand its ground when challenged. A good objective has clearly defined limits and can robustly demonstrate whether it has sufficient resources allocated. A good objective will give sufficient confidence for the conclusion to rest only in the facts: there is sufficient evidence to say yes, or there is insufficient evidence to say yes, but that does not mean it is sufficient to say no; the risk can be ameliorated, but not removed.

A good objective, indeed any objective, is not an answer but a question.

The answer the objective may achieve might be definitive, but in our imperfect discipline it will more often be a position within a threshold of probability.

The first question that will logically be asked is: is surveillance necessary?

In order to answer that question, the objective threshold adopted in this book is that of "reasonable likelihood".

"Reasonable likelihood" is enshrined in ODPM Circular 06/2005: Biodiversity and Geological Conservation – Statutory Obligations and their impact within the Planning System and within National Planning Practice Guidance.

ODPM Circular 06/2005

ODPM Circular 06/2005 states:

"The presence of a protected species is a material consideration when a planning authority is considering a development proposal that, if carried out, would be likely to result in harm to the species or its habitat."


"It is essential that the presence or otherwise of protected species, and the extent that they may be affected by the proposed development, is established before the planning permission is granted, otherwise all relevant material considerations may not have been addressed in making the decision."


"Bearing in mind the delay and cost that may be involved, developers should not be required to undertake surveys for protected species unless there is "reasonable likelihood" of the species being present and affected by the development."

National Planning Practice Guidance: Natural Environment – Biodiversity and Ecosystems

Paragraph 016 of National Planning Practice Guidance (NPPG): Natural Environment – Biodiversity and Ecosystems states: "An ecological survey will be necessary in advance of a planning application if the type and location of development are such that the impact on biodiversity may be significant and existing information is lacking or inadequate."


"Where an Environmental Impact Assessment is not needed it might still be appropriate to undertake an ecological survey, for example, where protected species may be present."


"Local planning authorities should only require ecological surveys where clearly justified, for example if they consider there is "reasonable likelihood" of a protected species being present and affected by the development. Assessments should be proportionate to the nature and scale of the development proposed and the likely impact on biodiversity."

"Reasonable likelihood": 'more-likely-thannot'

In the context of both pieces of guidance, "reasonable likelihood" means 'more-likely-than-not', which in fully accurate terms means >50% probability.

It does not, therefore, mean a vague potential, but rather a situation that is on the positive side of the 'probable' threshold, and probable requires proof; a foundation of robust scientific evidence.

Therefore, in an appraisal in support of a planning application, for every question we seek to answer we should provide proof on an increasing scale. Adopting the same principle in an amateur search would also be sensible, as it directs energy to where it is most likely to be rewarded. A list of example questions might include:

1. Is it 'more-likely-than-not' that tree-roosting bat species are in range of the site?

Can we prove it?

2. Is it 'more-likely-than-not' the site holds trees?

Can we prove it?

3. Is it 'more-likely-than-not' those trees hold Potential Roost Features (PRFs)?

Can we prove it?

4. Is it 'more-likely-than-not' those PRF are suitable to hold roosting bats of the species that are 'more-likely-than-not' to visit the site?

Can we prove it?

5. Is the combination of bat species, habitat and PRF such that it is 'more-likely-than-not' that bat roosts will be present?

Can we prove it?

6. Is it 'more-likely-than-not' that the operation proposed will affect any tree-roosts that might be present within the Zone of Influence?

Can we prove it?

7. Is it 'more-likely-than-not' that existing information is lacking or inadequate to inform an Impact Assessment?

Can we prove it?

8. Can we design surveillance that will be 'more-likely-than-not' to provide any missing or inadequate information that will be sufficient to inform an Impact Assessment? Fundamentally:

a. Is it 'more-likely-than-not' the surveillance will encounter each individual species of bat or evidence of bats if they are present?

b. Is it 'more-likely-than-not' that we will be able to conclusively identify any bats encountered?

c. Is it 'more-likely-than-not' that we will be able to count any bats encountered?

d. Is it 'more-likely-than-not' that we will be able to sex any bats encountered?

And if not ...

e. Is it 'more-likely-than-not' that if the surveillance does not encounter bats, we will be able to interpret the field-signs we have observed to either perform a robust appraisal based on the data available or to support a request for more resources?

And can we prove it?

Can we demonstrate that our findings agree with a body of evidence to which the readers of our report have access and can see for themselves that, while the surveillance may not demonstrate presence conclusively, it does support a statement of probability that is above mere potential.

Furthermore, can we demonstrate that the methods we have used and the effort we have expended in pursuing the objective were sufficient to support a robust conclusion?

And so, we come to proportionality.


The need for a proportional approach is enshrined within National Planning Practice Guidance, which requires that:

Assessments should be proportionate to the nature and scale of the development proposed and the likely impact on biodiversity.

Proportionality decides how much effort we expend pursuing the objective, and again we have the word 'likely'; not a vague potential, but a predictable probability that should be supported by tangible evidence.

The concept of proportionality might simply be thought of as a balance; a set of scales.

An example of proportionality might be the balance between the predicted magnitude of an impact in terms of timing, duration, extent and reversibility, versus the outcome of that impact (i.e. its effect). However, it might also be the balance between the loss of one area of habitat versus the gain of another, or the outlay in terms of appraisal effort versus the additional confidence the expense will provide.


Excerpted from "Bat Roosts in Trees"
by .
Copyright © 2018 Henry Andrews.
Excerpted by permission of Pelagic Publishing.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Table of Contents

Preface iv

Citing, Credits and Acknowledgements v

1 Rationale 1

2 Tree-Roosting Bats 12

3 Potential Roost Features (PRFs) 29

4 Intelligence-Gathering 79

5 The Desk-Study 87

6 Ground-Truthing 96

7 Choosing the Surveillance Methods 107

8 Close-Inspection 117

9 Remote-Observation 171

10 Static-Netting 193

11 Surveillance Effort 202

12 Trouble-Shooting 227

Appendix A PRF Summary Tables 239

Appendix B PRF Recording Form 244

References 245

Bibliography 250

Index 252

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