Success in the Bat House project
In 2006 we erected two 3 chamber bat houses on a house in Co. Roscommon. We were asked to do this by the owners of the house because a flat roof on the house was to be demolished leaving a maternity roost of 400+ soprano pipistreles homeless.
Both houses were constructed using plywood and soft deal timber. The exterior was painted with a water based black paint and the first few inches of the interior with a black water based stain. The house measurements were approximately 32in h x 18in w x 5in d. The chambers inside the house where the bats hang out are 24in h x 14in w x 3/4 in. All internal surfaces were grooved to provide grip for the bats. The houses were erected on the East facing side of the dwelling 15 ft high.
In 2006 when the bats returned to find their old roost demolished they bypassed the new bat houses and set up home in the chimney.
In 2007 small numbers of bats started to use the bat houses with a maximum count of 8 bats in August.
In 2008 only three bats were counted in July.
In June 2009 81 bats were counted leaving one of the houses (hse B). However it’s worth noting that the bats were present in large numbers in late may, but in early June the houses remained empty for 5 days during a hot spell of weather (27deg. c) That August 131 bats were counted leaving suggesting that the bat house had been used as a nursery. By October 16th all the bats had left.
In June 2010 148 bats were counted and by August the number counted had risen to 203 bats in one house (hse B) again suggesting that the bat house had been used successfully as a nursery roost or the second year.
The second bat house (hse A) which is only inches away seems to be following a similar pattern of use to house B with a count of 12 bats recorded in August 2010.
The bat houses were designed to attract a maternity colony of bats. The design provides close to 14 sq feet of roosting space in a relatively small structure. The open bottom plan eliminates the need for annually cleaning out droppings as they fall directly to the ground. This design also discourages wasp and bird nesting. The black colour of the houses attracts solar heat that the bats need in a nursery roost.
The houses should have been constructed with marine plywood and western red cedar timber. This would give the houses a much greater lifespan. We have now sourced better timber treatment products and liquid rubber membrane that will protect the houses from the elements while at the same time being bat friendly.
A dark stain applied to the entire interior of the house may attract bats sooner as they seem to prefer to roost in dark.
The costs involved in constructing bat houses with correct materials and then supplying them free is part of what we do and hope to continue in the future. But this has had an effect on the projects’ success. We now hope that by supplying a properly made bat house for sale will provide the required funding.
Little information is available on similar bat house usage in Ireland. In the UK a similar bat house had a total of 150 bats and claimed that was the largest number of bats in the UK using this type of house. That would make Bat house B the most successful bat house ever erected in Ireland or the UK, but we would love to be contradicted!
View from under house showing the bats roosting inside.
Bats exit at sunset