example of how a novel technique was developed.
Case Study 1.1 The development of a novel net for sampling bats emerging from tree roosts
BTHK Tree‐roost Net in situ. A schematic showing the pivot points to adapt the BTHK Tree‐roost Net ensuring optimum positioning against the tree.
Henry Andrews is an ecological consultant and the founding member of the Bat Tree Habitat Key (BTHK) project (http://battreehabitatkey.co.uk). The BTHK project was set up to achieve several objectives: (1) to establish the full range of different features of trees used by bats for roosting; (2) to understand which species used which features, when they used them, and how they used them; and (3) to build an app to help fieldworkers assess which species they might encounter in potential tree roost features. This case study describes the development of a new net by Henry Andrews of the Bat Tree Habitat Key project and NHBS Ltd to allow the user to sample bats emerging from tree roosts safely. This work involved a number of contributors: Henry Andrews, Katharine Clayton, Oliver Haines, Thomas Hamilton Koch, and Steaphan Hazell.
The BTHK Tree‐Roost Net is supplied by NHBS Ltd (https://www.nhbs.com), a company that manufactures standard and bespoke marine, freshwater, and terrestrial survey tools.
Model organism and research challenges faced
Of the 18 species of bat recorded in the UK, 14 are known to roost in trees (Bat Tree Habitat Key Project 2018). Little is known about inter or intraspecific differences in the use of tree features for roosting, or the extent to which different species use trees in different habitats or during different seasons. To fill this gap in our knowledge, the BTHK project collects and analyses records of tree roosting behaviour submitted by bat researchers, ecological consultants, arboriculturalists, and bat conservation workers. One problem identified by the BTHK project is the inadequacy of current methods to sample bats roosting in trees. Endoscopes are frequently used but provide limited data, because it is very difficult to identify bats to species level using this method (let alone record sex ratios!). Furthermore, bats frequently cluster in narrow crevices, making observation of more than one or two bats almost impossible. An alternative method involves sampling bats with a handheld net as they exit the roost, but no safe, reliable, purpose‐built net existed.
How the challenge was resolved
The idea for a bat tree‐roost net originated with Henry Andrews and NHBS helped develop the design and manufacturing process. The end‐product (the BTHK Tree‐Roost Net), employs a kite‐shaped head that pivots in two places to ensure optimum positioning of the frame against the tree. The aperture of the net head can be adjusted to fit a wide range of tree sizes (marked A on the figure) and the net head pivots according to the height and location of the roost entrance (marked B on the figure). These features mean that the net can be adapted to sample roosts at a variety of heights and orientations, safely and securely. The net handle is made from aluminium, which is both strong and lightweight, and at 4 m long it can either be placed on the ground or braced against the users' body to provide a stable foundation.
The collection bag is made from soft white nylon mesh to prevent damage to the bats wings and feet and enable the user to see the bats more easily against the white background. The collection bag also has a flexible plastic attachment that extends both into and away from the aperture of the net. This allows the outside of the collection bag to form around the contours of the tree, and acts like a funnel trap to prevent bats escaping from the inside of the collection bag.
Once the net has been set up, a thermal imaging camera can be used to monitor the contents of the collection bag. To minimise disturbance, Henry Andrews recommends that two to three bats are sampled from each roost, as in most cases this will provide sufficient information about the composition of the roost.
Advice for students wanting to work with bats
Bats and their roosts receive full legal protection throughout Europe and should never be disturbed without a license to do so. If you are interested in getting involved in bat research, you could volunteer with your local Bat Conservation Trust group (www.bats.org.uk) who will almost certainly provide opportunities for you get involved in bat surveys. You could also contact academics or ecological consultants that study bats to find out whether you could assist them with any of their work.
Creating aims, objectives, and hypotheses
Once a topic for research has been chosen, you can work out the aims of the study. These are important, since tightly defining the aims helps to focus more clearly on the work in hand and can avoid problems in implementation. ‘Woolly’ aims, such as ‘to investigate invertebrates under logs’, may be a starting point for a more focused aim, such as ‘to determine whether the number of invertebrates found under logs is related to the size of the log’. This then leads to further questions, including:
Which invertebrates are to be examined, i.e. should they be identified to species, or merely counted en masse, or allocated to ecological functional groups (e.g. predators, herbivores, etc.)?
What is a log (i.e. when is a fallen piece of wood a log rather than a twig?) and how many logs should be investigated?
How should we standardise or otherwise account for the condition and type of the logs (degree of decomposition, species of tree, etc.)?
Which measurements of size should be incorporated (e.g. length, width, surface area touching the ground, volume, depth of log in the soil, presence of other organisms such as fungi, etc.)?
Where should we sample the logs?
Which statistical method(s) should we use to analyse the data?
Once these questions have been answered, they become objectives that can be used to determine your methods. The aims and objectives lead us to the setting up of working hypotheses. For example, in our study of possible relationships between log size and the numbers of invertebrates found beneath them, we would set up a statistical hypothesis to be tested. It is common practice that the statistical hypothesis to be tested is a null hypothesis; in this context that ‘there is no relationship between log size and the number of invertebrate animals found underneath them’. Most univariate statistical tests examine the likelihood of the null hypothesis being true (see Chapter 5). A null hypothesis should meet the following criteria:
be a single, clear and testable statement – where more complex research questions are asked, you should break these hypotheses down into individual statements that are treated separately and tested in turn;
have an outcome, typically either ‘accept’ or ‘reject’ the null hypothesis;
be readily understandable to someone who is not a scientist.
Reviewing the literature
You should always review the
