Bat House Forum

[IowaNate]

 This spring I will be putting up four to six bat houses with crevice widths of 5/8" at my local Nature Center preserve.

  I may be going backwards in the overall size of these houses though, as each house will only be 18" tall and 12.75" wide with two 5/8" crevices. Interior dimensions will be 15" tall and 11.25" wide. I will be putting a 1/4" vent 5" from the bottom of the front and paint each house dark brown. Each house will be constructed of 1x12's and 1x4's. No screening will be used, I am going to use rough cut 1x12's or horizontal grooves for gripping.

  I will mount the houses on utility poles in pairs or in threes. If I mount them in pairs, one will face SE and one will face SW. If in threes, they will face East, South, and West. They will be between 10 and 14 feet from the ground and within 100 yards of open water. The will be in direct sunlight for atleast 6 hours of the day in the summer.

  I have observed one Eastern Pipistrelle for three years at this site, roosting in a 5/8" crevice underneath an elevated deck, and the crevice was just 9 feet from the ground.

  If no bats choose to roost in these houses I won't be out of alot of time and money, but I am hoping that a few might use them in the next summer.

  Any comments or suggestions will be greatly appreciated!

[Terry Lobdell]

Nate, I have a couple houses with approx. 5/8" crevices which get a lot of use from little browns. The crevices are probably a shade over 5/8".

That is interesting that you've seen an eastern pipestrelle. Have you told Mylea Bayless about it?

I often wonder if I have other species besides big and little browns in my houses.

I definitely think more experimentation which 5/8" crevices would be good!

[Erik]

Hi Nate,

in  the Netherlands we use cm instead if inch so had to convert to cm. Do you mean 0.625 inch (= 1.59 cm)?
I think that is a good idea. We have two pipistrellus species in the Netherlands and both like to roost in narrow crevices. We have found out that these bats particularly like bat houses with crevices that are wide at the bottom (2-2.5 cm = 0.79 - 1 inch) and very narrow at the top (1.2 cm = 0,47 inch or even less). We observed that these bats very much like to roost in to the crevices they hardly fit in. They crawl as high as they can in these crevices. Maybe because it gives them a sense of safety, being out of reach for predators?  Of course you have different species of pipistrelle bats but if the Eastern Pipistrellus preferes small crevices they also might like these kind of bat houses?

So I think it is a very good idea!

Erik

[IowaNate]

 Erik, your measurements are correct. And the Eastern Pipistrelle is one of the smallest bats in my area (wingspan between 222 and 250 mm and overall length with tail is between 77 and 89 mm).

  I have only seen three in the wild where I could positively identify them, but they are supposed to be quite common.

  We will see what next summer brings for these new houses!

[IowaNate]

 At the expense of making the bat house 1.5 inches less in width, I am going to add a third chamber. Overall the house will be 11.25" wide and 18" tall. Each partition will be 9.75" wide and 15" tall. I know the house is getting pretty small in terms of the average bat house, but I am currently limited to 1x12's and 1x4's for construction and mounting it from a ladder by myself.

  I am taking a suggestion from Erik and making the rear chamber 3/4" at the bottom and tapering to 1/2" at the top. The other two chambers will be 5/8" throughout with a 1.5" hole in the middle of each to permit bats access to every chamber. The houses will be more of a European size, but with North American crevice orientation.

  If these houses are occupied by any significant number of bats (6 or more) I will make larger houses with 5/8" crevices, even if they are not pipistrelles.

  Below is a scale cut-away view of the proposed house, each square is 1/2".

[Terry Lobdell]

Nate, I've had good luck with bat houses having baffles approx. 12" in width. And the narrow widths certainly does make them easier to mount.

I know BCI recomends baffle widths of 14" or more which makes sense if you already have a lot of bats for have the potential to attract large numbers.

From my experience the main advantage of a wide baffle is if paper wasps build nests there is room for both the bats and wasps. I built a lot houses approx. 24" in width but they are a pain to mount because of their size.

I think in the future for experimental or simple single crevice starter bat houses  I am going to build a more narrow width house.

They will be easier and less expensive to construct and easier to mount.

If mounted on a building there will be more options of mounting locations because of the smaller size.

[IowaNate]

  I agree Terry. I have had good success with 12" wide houses, where the actual roosting chamber is only 10.5" wide (hence the occupied houses on my home currently) and the houses weigh less than 10 pounds for ease of mounting, the cost of each house is usually less than $10.

  What you lose in wide temperature gradients with one large house, you gain some back by being able to orient a few smaller houses near each other.

  Since I am mounting these on 8" to 10" utility poles, I can mount two to four houses at the same level facing different directions. I gain some temperature stability by using 3/4" lumber and the utility pole itself. I know I probably won't get a nursery colony of any species to move in, but that's not the purpose of the experiment (not YET anyhow ;))

  On a slightly different note, I researched Eastern pipistrelle nursery colonies and came up with a study in Massachusetts of a colony in a barn. The temperatures through a four month period during birth and rearing of the young ranged from 67 to 91 degrees. Perhaps pipistrelles like it slightly cooler than other species, which could be another reason that so few pips occupy bat houses.

[Terry Lobdell]

Nate, that is good info about the temps.......where did you find that at?

[IowaNate]

  Here is the link to many bat publications by Thomas Kunz. Most of them are in pdf format.  http://www.bu.edu/cecb/BATS/publications.html

[Terry Lobdell]

Nate, that is an excellent link! Thanks!

[IowaNate]

  The first two "pip" houses are done. I added a 5/16" hole to each side of the rear chambers (see photo) since there could be a great possibility of overheating with these smaller houses. But I made them two different colors as well, dark brown which is my standard, and medium brown. I am only going to build four of these (I'm laid-off so funds are tight) and one of each different color will be mounted in pairs. I have high hopes for these houses, if anything they should be home to a few little browns, but I am praying for a few pipistrelles! The last photo shows a quarter in the house for size comparison, the angle makes the houses appear to be slightly different sizes, but I can assure you that they are exactly the same.







 

[Terry Lobdell]

Those look good Nate, I drill holes in the side also for ventilation. I have also had good luck with sawed kerfed baffles. I would like to try a dado setup to do multiple kerfs. Maybe you can give me some ideas on that?

[IowaNate]

 Wish I could help both you and me on that. I set my 7.5 inch circular saw to 3/32" deep and cut at every 3/8" on the baffles. It's quite labor intensive. I have big problems finding rough cut lumber that is even remotely straight in my area, so it's either find straight sanded wood and cover it with pet screening or cut saw kerfs in it.

  On another note Terry, I would be cautious of using oriented strand board in bat houses. I have seen it warp, pull apart, and fall apart when exposed to moderate moisture after 3 years. Granted, it is inexpensive and easy to use like plywood, but the long term life of the OSB is far less than plywood when exposed to bat urine or moisture. Now I am speaking of untreated OSB...if it were painted and covered with pet screening, it might last far longer.

 I am starting to hop on the Kent Borcharding boat and use only 1" to 2" lumber for my bat houses if they can be installed without too much difficulty due to the higher weight. Most of my current bat houses last about 10 years before needing some serious repairs.

  Ugh, if I had the time and money, all my houses would be made of 1" to 2" lumber with saw kerfs and hung 15 feet in the air.

[Terry Lobdell]

Nate that is good info about the osb. I just purchased a sheet of 7/16" this fall for use as baffles in 2 bat houses. I've glued pet screen on both. These houses will be mounted in state parks so I will watch them for deterioration.

On the subject of one and two inch stock, I agree that it has the potential to be the longest lasting material for bat houses.

I also have been paying attention to Kent's theory that the bats like it because it holds night time temps longer. I believe he says 5 degrees warmer at night than 1/2 or 3/8" plywood. I have one house made with one and two inch stock that my big browns really like and I'm thinking it could be that it holds the night time temps better.

This fall I was able to have some timber cut and sawed into one and two inch stock. Mostly red pine, quite a bit of larch and quaking aspen. Much of the red pine appears to be rough enough to make good baffles as is. I plan on building several bat houses with saw kerfed, scored and just rough sawn baffles.

[BatMan]

Very nice Nate...makes me want to go out and buy some wood to make some more houses. Although like both you and Terry mentioned it is very tedious cutting those kerfs. That's the only way I've built all of my houses, I have yet to do the screening.