Certified Bat Friendly Shelters
North American bats are not so much compatible with the commercial bat houses due to several reasons. The reasons may be poor design or construction. It is also possible that proper instructions are not given on placement, painting, mounting and sun exposure. To help the manufacturers in designing a bat house, BCI’s Bat Approved Certification Program started in 1998. This program provides detailed guidance to the manufacturers. BCI ensures that all the bat houses and products from other companies meet the criteria in its catalog. To finalize the criteria of successful bat house installations was not an easy task. It involved several years of research for the BCI and volunteer Research Associates in Bat House Project (1993-2004).
Finally, the following criteria were found important:
To get greater temperature diversity, wide and tall designs are preferable Proper crevice dimensions are also preferable Roughened interior and landing areas Ventilation slots Tight, draft-free construction Based on the above set criteria, it is mandatory for the manufacturers to submit a finalized bat house for evaluation. If all the above criteria are met, only then the manufacturer gets the Bat Approved certification. One important point to note here is that the certifications are valid only for two years. The bat house instructions must be re-evaluated after this period.
Following are the Bat House Design and Construction Certification Criteria:
1. Taller chambers are considered better. The recommended height of roost chambers is minimum of 20 inches.
2. Larger width or side to side is considered better. The recommended width of roost chambers should be at least 14 inches. Rocket style houses which have continuous or 360 degree chambers are less wide. Different material can be used for bat houses and roost chambers of such houses could be wider than 16 inches. Spacer blocks should be used between partitions.
3. Irrespective of the number of chambers, you should ensure that roost partitions are carefully spaced 3/4 (ideal for North American bats) to 1 inch apart from front to back. An exception in this area is the houses built for larger species such as pallid bats and Florida bonneted bats. Chambers are spaced in a combination of 3/4- and 1-inch. Chambers spaced with 1 1/2-inch are considered more attractive to wasps and other non-target animals. Such chambers need regular monitoring. This should be advertised for these special species.
4. Suitable landing area is another important aspect. Preferred landing area is three- to six-inch, that should extend below entrance; i.e. by extending the length of backboard. Partitions should be gaped three-to six-inches. This will allow the bats to land on inside walls of bottom of the bat house.
5. Sufficient interior surface and landing area texture is the next concern, which will help bats in footholds. This can be achieved with rough-cut wood, mechanically grooved surfaces, roughened or scored horizontally at 1/4 to 1/2-inch intervals, which are about 1/16-inch deep. Cover roost surfaces with a durable plastic mesh, preferably 1/8- or 1/4-inch square mesh. To avoid the twisting and dropping of the plastic mesh, firmly staple the plastic mesh every two inches - up, down and across. Trim the edges of the plastic mesh to avoid sharp edges. Avoid hardware cloth, metal mesh or aluminum window screen. These materials can harm bats.
6. While installing houses, staples, screws, mounting hardware, nails or other sharp objects like splinters should be adjusted properly and these should not protrude into roost chambers. You should also ensure that all hardware and metal components are coated, brass, or galvanized. The holding capacity of nails, brads or staples degrades over time. Hence, screws are recommended to assemble all possible major components of the house. It is recommended to use smooth exposed metal edges such as roofs.
7. The distance between the bottom and ventilations slots should be not more than one-third. Depending on the wideness of the house, front vents are designed wide. Side vents are optional and its dimensions should be approximately six inches tall and one inch wide. You can also go for decorative vents with appropriate size and position. In case, a bat house is designed for cool climates, unvented wooden houses can be used. Again, it should be well-stated in advertising.
8. Exterior grade plywood - ACX, T1-11, BCX with quality stock such as cedar or pine should be used if need be. To avoid destructive actions on bats, pressure- or chemically-treated wood should be avoided.
9. Design should say it all. Durability of bat houses is very important. Ensure that the bat houses are tightly constructed - no unplanned gaps. During assembly, to prevent draft, glue exterior joints. Latex caulk and exterior-grade, water-based paint or stain is recommended for caulking and painting. However, sufficient instructions must be provided for the customers on these.
10. BCI should approve every little instance of advertising and instructions of the bat house. Many manufacturers state misleading claims such as "No more mosquito problems". Such claims should not be permitted. Instruction sheets with adequate information on painting, sun exposure, mounting sites, mounting height and recommended distances to water and obstacles will surely get approved by BCI.
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