There is little reason to evict bats from buildings where they are not causing a nuisance. However, bats should be prevented from entering human living quarters and in some instances, noise or odours from large colonies of bats can become a nuisance.
Excluding bats from a dwelling is the only long-term control method for bats who are a nuisance in a building. It can be fairly straightforward, but is often not, requiring some expense and a lot of effort. When people realise this they often elect to simply rather live with the bats, especially if there are not problems such as odour or noise.
The idea is to permanently seal all holes, except for the main access point, which is fitted with a one-way valve. After waiting a few days for all the bats to exit without being able to re-enter, the valve is removed and sealed permanently.
Step 1 – Find the main access point
Inspect your house for markings, droppings or physical presence
A simple inspection of the outside of the building can be made to determine whether bats are living in and where they are entering. Look for staining at the access point and/or droppings below. Bats usually enter a building at the roof/wall joint, under loose fascia boards, or through broken vents or other cracks resulting from building deterioration. Bats can crawl through openings as small as a pinky finger. If the access hole is hard to find it may be necessary to do a stakeout and watch for where bats exit at dusk.
Watch out for bats leaving their roosts at dusk.
The bat watch should be started about 30 minutes before dusk. Station enough people around the building so that the entire roof and wall area can be kept under constant observation. If bats are present, they will start leaving the building about dusk; the last bat should come out of the building within one hour of the first bat. All bat exit and entrance points should be noted, as well as the number of bats. This procedure may take several evenings to accomplish, but it is useful to identify all bat holes.
Step 2 – Fit a one way valve over the main access point
One-Way Valve made from netting or sheeting
Plastic or lightweight, flexible netting with 0.4 cm mesh or smaller, is secured to the building along the top and sides of the opening to allow bats to exit, but not return, as shown in the diagram below.
An easier and cheaper option is to substitute with plastic sheeting like that used in roof construction or for drop sheets when painting.
After this has been done, watch to make sure the bats are able to exit safely. If they do not appear to be exiting, or appear to be having trouble doing so, it may be necessary to make adjustments or add new valves as needed.
One-Way Valve using PVC Pipes
There are a number of situations in which tubes work better as bat exclusion devices.
Examples include openings used by bats on buildings constructed from materials that do not create flat exterior walls, such as those found on brick or stone houses, and log cabins. Tubes also work best for holes located at corners where walls meet and on horizontal surfaces.
Exclusion tubes should have a 5 cm diameter and be approximately 25 cm in length. It can be made from PVC pipe or flexible plastic tubing. Use of a flexible plastic tube makes it easy to either squeeze one end of the tube so that it fits into a crevice, or cut one end of the tube into flaps that can be fit over an opening and stapled, nailed, or taped to the building (see diagram below). Bats are unable to cling to the smooth surface of these tubes. Once the tube has been inserted over the hole, a piece of light weight, clear plastic can be taped around the end of the tube that projects to the outside to further reduce the likelihood of bats re-entering, though this is typically not necessary.
Step 3 – Seal all other holes larger than your pinky finger
This can done in various ways, depending on cost and availability of materials. Simply stuffing newspaper or plastic bags into the hole will work because bats are unable to chew or dig and at best can squeeze through gaps. But although it is not really necessary to use serious sealants e.g. polyfilla or concrete, it is better in the long run since it will last longer and will be impervious to rats which are able to chew.
This part of the exclusion can be the most challenging since it can be difficult to find all possible access points, and some are almost impossible to seal. Also, if it is a multi storey building then scaffolding may be needed.
Thatch roofs in particular can provide a headache. In this case something like chicken wire may be required to prevent access, but this looks unattractive and eventually rusts away over the years. It is at this point that many people simply give up and decide to live with the bats.
Step 4 – Wait a few days for all bats to exit
Bats do not leave every night. Like humans, sometimes they may stay indoors due to rain or cold weather. Therefore it is important to wait a few days to be sure all the bats have left and have been unable to re-enter. If they have babies (pups) which cannot fly, these are left in the roost while the mothers forage. Hence the reason for avoiding the maternity period.
Step 5 – Remove the one way valve and seal permanently
At this stage you may find that the bats have found another way in due to the difficulty of finding and sealing all the holes in Step 3. In this case the process must be repeated with the one way valve fitted on the new access point.
Bat-proofing has two potential drawbacks.
One is that exclusion can be stressful for a maternity colony. When prevented from using their usual roost, the bats may move into a nearby building, where they may be expelled again, or even exterminated. Also, research has shown that displaced colonies will not relocate into buildings that already house other maternity colonies. In other words, an excluded colony cannot necessarily just move down the road into another house that already has bats. If a displaced colony cannot find a new roost, it may leave the area.
A second drawback is that homeowners may find it difficult to bat-proof their home completely. Bats can crawl through cracks as small as 0.5 - 1cm, so persistent bats may find a way to re-enter their former roost.
Bat houses can solve both of these problems because they provide alternative roosting sites for maternity colonies. When constructed properly, bat houses can serve as suitable places for females to raise their pups. The bats get a safe roosting site outside the home, while homeowners benefit from the bats' control of insects. The problem here is that often bats simply do not utilize the house provided, for reasons that are seldom obvious. In this case, chances that they will move into the bat house can be improved by erecting more than one at various places.