Northern Prairie Wildlife Research Center
Although exclusion is the only permanent answer, bats may be trapped alive before batproofing. Griffin (1934) was the first to collect live bats from inside buildings with a "trap roost" attached to the underside of the attic roof ridge where bats often hang. When the bats were disturbed, they retreated into the pockets of the trap instead of into the cracks between the boards of the building. To collect bats as they left buildings, Griffin (1934) devised a variety of traps (tunnel nets and traps, plastic cylinders); their design and use are described by Greenhall and Paradiso (1968; Fig.18 bottom).
|Fig. 18. Types of traps that will collect house bats: top-Constantine harp trap; middle-Constantine plastic trap; bottom-Trap locations on a house. (From Greenhall and Paradiso 1968)|
A hopper trap for use around buildings that harbored Mexican free-tailed bats was invented in 1962 by Davis et al. (see Greenhall and Paradiso 1968; Fig. 19). These traps provided storage space for captive bats, so it was possible to set traps in several towns and run them during daylight. The hopper trap is made of black plastic or oilcloth fastened over a wire frame 80 cm (32 in.) high with each side 70 cm (28 in.) at the top and 22.5 cm (9 in.) at the bottom. Below this is suspended a 40-cm (16-in.) deep mesh holding bag, with a drawstring to close each section at the bottom. Another useful feature is a hook attached at each top corner so that, when necessary, several traps may be fastened together like a "nest" to increase the catching area. When using this trap, the size of the exit hole must first be reduced by gluing a slick plastic shield around it. An extra shield must be provided so it will overlap the edge of the trap, which is set at the minimum possible distance below the exit.
|Fig. 19. Details of R. Davis' hopper trap. (From Greenhall and Paradiso 1968)|
An unusual harp-like trap made of steel piano wires was designed by Constantine (1958) to snare large numbers of free-tailed bats (Fig. 18 top). Constantine (1958) also discovered that bats will fly into clear glass or transparent plastic sheets placed vertically at building roost exits (Fig. 18 middle). After striking the obstruction, the bats slide into a smooth-sided container below.
Constantine's trap has undergone numerous modifications. Thin monofilament nylon fishing line may be used instead of steel piano wires. Aluminum tube frames may be used to reduce weight and a double frame of strings improves its effectiveness (Hamilton-Smith 1966). These modifications have been described by Tuttle (1974a, 1974b) and the efficiency of the trap has been discussed by Kunz and Anthony (1977). Little brown bats were trapped at barn sites by Anthony and Kunz (1977). Tidemann and Woodside (1978) developed a lightweight 7-kg (about 15-1b), collapsible bat trap based on the original designs that can easily be carried and assembled.
A simple, effective bat trap devised by the owners of an old Michigan farmhouse has been described in The Old House Journal (Anonymous 1980a):
We bought our 100-year-old farmhouse in the early spring. It was two months later that we discovered bats were living in it too. After trying to get rid of them by scattering moth balls in the attic, which was the only practical solution that anyone suggested, we were relieved when they went into hibernation in the fall. This spring, there were more bat droppings than ever on our windowsills. Some had died off in the winter, but there were still about 200 living with us and probably multiplying. We came up with a bat trap which has taken care of the problem. We can now seal up the holes without worrying about the bats finding another exit through the house or rotting inside the walls. The bat trap works on the principle that in order to start flying the bat must first fall out of the hole far enough to spread his wings and begin a glide. We bought a piece (1 1/2 yards) of cheap, sheer curtain material which we sewed into a funnel wide enough at the top to cover the bat-hole and small enough at the bottom to fit over a piece of metal tubing about a foot long (we used a piece of dryer vent). The metal tube is too slippery for the bats to climb up and too narrow for them to fly out. The cloth was securely taped to the pipe and a plastic garbage bag was attached to the other end. We then stapled the top of the funnel to the bat hole at dusk. The cloth should not sag or the bats will catch themselves before entering the pipe and start to climb back up. Then we sat down to watch. The bats fell down the funnel, through the pipe and into the bag ....The beauty of this device is that no one touches the bats. After just a few nights, the bat population was nearly exterminated. Our next step was to seal the hole so they would not return. (See Fig. 20)
|Fig. 20. Effective bat trap. (Courtesy "The Old House Journal")|
Traps require little attendance (unless thousands of bats are present) and, after the bats are in the trap bag or container, the animals are protected from weather and most predators. D. G. Constantine (personal communication) cautions that squeaking bats may attract some predators, such as raccoons and cats, which will enter the traps and eat the bats.
Buildings from which bats have been trapped for transplanting must be batproofed to prevent their reentry because bats have strong homing instincts (Davis and Hitchcock 1965; Griffin 1970; Leffler et al. 1979). Live bats should be handled only by rabies-immunized professionals (D. G. Constantine, personal communication).