Читать книгу Practical Field Ecology - C. Philip Wheater - Страница 26

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.