Best practices
for nuisance wildlife control operators in New York State

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Ch 5 : Step three: Do it - Nonlethal techniques

One-way doors ("check-valves")

One-way doors may look very different, but they all do the same thing: let the animal out and keep it from getting back in. Above, left: Looking into the device, you can see its trap door in the set position. At right, the same one-way door design, used to remove flying squirrels from an attic. If you opened the left-hand side of the device, they'd leave on their own. Bottom: Mesh is often used to make a one-way door for bats. This one-way door design is usually called a "checkvalve."

These devices allow an animal to leave but not re-enter a building. They come in a variety of

 designs, sizes, and materials, from plastic checkvalves or nets used for bat control, to wire frames that are specially designed to fit certain cage traps. Some NWCOs build their own one-way doors. One of the advantages of using this tool is that you don't have to handle any animals. This is a relatively new tool in nuisance wildlife control, but its use is increasing.

Before installing a one-way door, conduct a thorough inspection to make sure there are no young present which are still immobile and dependent on their mother. One-way doors are only effective if the animal can find and use the exit but cannot find, or force its way back through the door—or find another way into the building. Remember, if a mother has been separated from her young and they're still inside, she will be highly motivated to find another way in.

Here's how a one-way door is used in bat control. A commercial checkvalve or simple netting is installed over the bat's primary exit hole. All the other holes are sealed. Bats exit at the bottom of the one-way door, but when they attempt to return, their sense of smell guides them back to the hole. They land on the mesh (or checkvalve) near the hole, and stay there, sniffing around. They just don't crawl down the mesh. After a suitable period of time, the one-way doors are removed, and the main entry sites are closed. (For more information, see the "house bats" account in Appendix B or the Cornell Cooperative Extension's video, The facts about bats: Exploring conflicts, designing solutions.)

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