A mobile trap for capturing bats in flight

(based on: Borissenko, A. V. 1999. A mobile trap for capturing bats in flight.
- Plecotus et al., 2(1999): 10-19. [in Russian])

Fig. Diagrammatic view of the mobile bat trap: а) attachment of the upper edge of the net to the pole; b) attachment of the lower edge of the net to the pole; c) attachment of the elastic line to the pole. Drawing by V. V. Rosina.

The existing methods of capturing bats in flight, such as harp traps and mist nets, are highly dependent on accident imposed by the probability of the bat to become captured, which makes them practically inapplicable under certain circumstances. This provides for the necessity of elaborating a technique enabling the catcher to directly affect the capturing procedure.
The method described herein, provisionally named as the mobile bat trap, or "flap-trap" is a technique enabling to conduct active capture of bats as they pass within a given range from the catcher. Ideologically it resembles to some extent the "flicking" method, suggested by Finnemore and Richardson (1987; cited after: Jones et al., 1996), although it is essentially different.
Basically, the mobile trap consists of a fine kapron (nylon) net stretched between two poles (Fig.). A 3 by 2,3 m net with a mesh of 14-18 mm and 0,1-0,15 mm thread diameter and should be threaded along the edges by a 0,5-1 mm rope frame, to form a trapezium-shaped shallow scoop ca. 2-2,5 m wide and 2 m high, with four loops at the angles. The poles are made from 4-5,5 m glass-plastic or carbon-plastic fishing rods. The lower loops of the net are attached to the poles via an elastic line, and the upper loops are fastened to the upper ends with a slip-knot, leaving free ends of ca. 15 cm.
The poles are held by the catcher under the arms and the bats passing within range are scooped by sidewise movements of the net. Head torches and heterodyning ultrasound detectors are most useful in aiding the catcher to be aware of approaching bats and in tracing their flights paths.
The trap proved to be quite effective in capturing a number of low-flying bat species, particularly, pipistrelles, mouse-eared bats, and small rhinolophoids in habitats where the probability of capturing them in mist-nets was low. The efficiency and ease of using, together with the possibility to make captures parallel to conducting field observations of chiropteran flight behavior makes the mobile trap a useful addition to the traditional methods of capturing bats in flight.