Bat House Forum

[Terry Lobdell]

Welcome Dave, it sounds like you have some really good ideas there! Here are my answers to your questions:

1. I don't think you need to ventilate the interior if there is plenty of ventilation in the outer crevices.

2. Your ventilation height sounds about right......about a third up from the bottom.......I might make the gap a little narrower....maybe 5/8" instead of one inch......reason being to cut down on light entering......Big browns will roost on the shadier sides when it gets too hot......

3. For roof slope I would say 10 degrees (roughly a 3 - 12 pitch) is about as low as I would go for a low sloped roof. You could go nearly flat if you cover it with one piece of aluminum.

4. I would gap the interior crevices at least 1/2" up to 3/4" to allow easy interior movement........

5. Your vertical vents I feel don't have to be as wide as the crevice.........1/2" to 5/8" would be plenty.......the six inch height for them is good..the bats will also enter and exit these places too..........Bats truly seem to love multiple vents/enter/exit points.......

6. As for the 2nd bat house, generally speaking the bigger the better...........It sounds like you will probably have enough temperature variation in your larger box.

This sounds like a rocket style box built around the spruce tree?

What part of the country are you located?

One thing to keep in mind.........I've never had a maternity colony of little browns share a box with a maternity colony of big browns..........But I suppose it could happen...........

Your design is definitely good to attract both species though........

My guess is if you are at a lower elevation near a stream or lake you will get little browns.......

If you are at a higher elevation you might get big browns........

Good luck and I hope you post some pictures!

[Dave M]

Thanks for the quick reply with the answers I needed. Please clarify one thing for me though, you say that big brown bats will be able to pass through gaps that are only 1/2" - 3/4" wide, while the crevices they roost in are 7/8" to 1" wide? I just want to be sure before I begin.

To answer your questions, I am in Rochester, MN (the SE part of the state). My plan is not a rocket box style. The tall stump is simply going to be the post, and a sturdy box shape frame will be built around and over it. The bat house chambers will be mounted onto the box frame. Imagine taking four bat houses that each have 3 or 4 crevices and are about 3.5 feet wide and 3.5 feet tall. arrange them in a square so that the corners are touching and that a few holes in each corner will connect them so that a bat could climb through from one into the next, and be able to make a circuitous route back to the starting point. A large roof will then be added to cover all four boxes and enclose a dead air space around the top of the stump. Of course I'll also have to build in some type of floor for the dead air space and seal it with some spray in foam to make it as air tight as possible. Don't worry, the foam will not be in contact with the bat house crevices, I don't want them to be exposed to anything chemical.

As to getting both big and little brown bat maternity colonies in the same bat house... I'm just a sucker for a challenge and I think I just might be able to pull it off. As you can see, my bat house design can really be broken down to four bat houses linked together. If two of the four are designed primarily for big browns, and the other two are designed for little browns, then why not? I believe I see both species feeding in my backyard every night when I'm out there during sunset in the summer. Has anyone had a maternity colony of each species in separate houses that are in close proximity to each other?

For more information, you can look back to my post from March of 2010:
maternity-bat-house-foot-tree-stump-t803.html

[William Bagwell]

Dave, went back to your earlier thread and I have a concern with the rot resistance of a spruce stump.

http://www.fpl.fs.fed.us/documnts/fplrn/fplrn153.pdf

Be a shame to build such a large and elaborate house only to have the 'pole' rot and fall down while the house still has years of useful life left. The other Dave who made the slate exterior houses had no choice but to use a dead tree since his went in a preserve that would not allow him to use a pole of any kind.

Can not really offer constructive criticism on the rest of your design since I'm kind of new to building bat houses as well. Other than to say it seems like a good plan to me.

[Dave M]

Interesting stuff concerning how long it takes wood to rot. Spruce doesn't look too good, but it's what I had growing there. It was healthy until I cut it last summer (2010). The rotting wood table discusses wooden fence posts, and it looks like a spruce post might last 5 years or less. Fortunately mine is an entire tree, I measured the circumference at heights of 1 and 5 feet, the circumferences are 52 " and 45" respectively. A bit of math and we have diameters of 16 and 14 inches, quite a bit bigger than a wooden fence post. Also, there are no cuts below ground, so I imagine that all rot would need to begin at the outside and work it's way in. There is a fork near the top of the stump, and I think each fork has a diameter of 6 inches or more where they were cut. The entire fork and crotch will be enclosed and protected by the bat house, so I don't expect that area to rot.

I expect the spruce stump/post to last at least 10 years, it would be great if it lasts for 20, but will probably end up somewhere in between. I just thought it would be much sturdier than anything I could erect (especially considering the size of the bat house), it's free, and it's in a good spot.

What do others use for posts, how long do they last, and how big are the houses mounted on them?

[Terry Lobdell]

Dave, big browns will have no trouble at all passing through 1/2" gaps.......most gaps I have between interior baffles are about 5/8".

All that I have read and observed big browns seem to prefer 7/8" crevices. One inch crevices are more likely to attract wasp nests.........I have also had my big browns roost in 3/4" crevices many times.

Here at my home I do have a maternity colony of each species. I have about 16 big brown mothers and about 60 little brown mothers. The big browns roost mostly in boxes mounted to my home and the little browns roost only on poles surrounding my yard. The big browns change roosts much more frequently than the little browns do...........My big browns will use up to 12 different boxes throughout the season and my little browns use only about 3 or 4.

As for you spruce post, I would just sink a couple treated 4x6's beside it and clamp them onto it somehow.......

The last couple years I have been making a lot of hollow poles with 1x6 or 8"s sandwiched around 2 x 6's......it makes a really strong pole and it ends up being much straighter than a solid 4x6. Almost all 4x6's end up warping and twisting in the sun......

I have a lot of my own larch lumber which is very rot resistant but treated boards could be used as well......

[Dave M]

Terry, thanks for all the advice, once I get the materials and begin building I'll post some photos. It will be a while though, I'm still looking for free/cheap wood that will work well.

[Terry Lobdell]

Dave, you might get some good usable lumber from some old pallets.........I've used pallet wood in bat boxes with good results.........

Another good source are sawmills........here in PA many sawmills give a way edgings free........among these edgings quite often you can find larger pieces of 5/8" and 3/4" thick boards that were too thin to be sold as one inch rough sawn lumber........

[Dave M]

I was given 3 pallets for free last fall and thought they would be good. Problem is they used spiral twisted nails that are extremely tough to pull. I need most of my boards to be around 40 inches long. For shorter boards I could cut the pallets apart, but that won't give me the length I need. Perhaps if I could get a saw in to cut the nails it might work. How did you do it, or did you just use short pieces?

[Terry Lobdell]

I might try getting in there with a reciprocating saw with a metal blade to cut the nails.........

Another thing that might work is a multimaster with a metal blade........I recently bought a dremel version of the multimaster and it is definitely a nice tool!

When I have taken pallets apart, I didn't have to deal with spiral nails......

[Joe Spencer]

Terry,
Great pictures and ideas. I'm looking for some advice from you though, because I'm very close to beginning construction on my own bat house. I'm hopeful of having a maternity colony of both little browns and big browns. My house will be built around the top of a spruce stump that I left over 20 feet tall in full sunlight, and the box will be in the neighborhood of a 40 inch cube. Each of the four sides will have 3 or 4 crevices, so it will have at least a dozen crevices in total. I plan to use kerfed boards, rough cut if I can get them, I may also have access to some weathered barn boards that are very coarse on one side. I'm considering a 5" landing pad, and crevices 37" tall and 36" wide, although the north side will be more like 24" wide. The crevices will have varying widths (3/4", 7/8", and 1"). I'm thinking of making the north and east sides more ventilated with the wider crevices, and the south and west sides narrower with less ventilation, hopefully providing good places for both species. The center of the box surrounding the trunk and the attic above the crevices will be a single sealed air space which I expect to get hot during summer days. This hot space will provide heat through the wood to the inner crevices, while the outer crevices will be cooler. I plan to have black shingles and paint the box black. I think the interior hot air space should not go all the way down to the bottom of the crevice, but rather stay 1/3 to 1/2 way up from the bottom, so that it only heats the top portion. I'm also thinking of painting the top half of the sides black and the lower half of the sides lighter for more heat variation. I will build a frame using 2x6's and 2x4's surrounding the top of the stump, then I will use french cleats to attach each side, and finally add the roof.

I want the roof to be low with a shallow slope to minimize size and weight, how much slope do you recommend if I use tar paper and shingles?

Do you think the interior heat chamber will get too hot and that it should have some kind of vent?

How wide should the gaps between the boards be to allow big brown bats to move between crevices within the house?
By the way I'm also going to have vertical gaps about 6 inches high in some of the corners to allow bats to move around the house, from the east side to the north side for example.

Given a 3 foot crevice height, how high should I place the horizontal vent on the outermost crevice, and how wide should the vent be? I'm thinking about a foot high and 1 inch wide.

I'll have vertical vents on the ends of each crevice too, I'm thinking about 6 inches tall and as wide as the crevice, any idea on how high I should put them, or if they are about the right size?

Once this main house is up I want to attach a smaller house beneath it on the north side. This smaller one will be for use in hot weather, it will be painted a light color, have tremendous ventilation, and 7/8" or 1" crevices. How wide and tall do you think this should be? I vaguely recall that I believe you had a bat house mounted on a chimney where big browns occupied the cooler space between the box and the chimney.

I hope I didn't bog you down with too much detail, and any advice will be appreciated. Of course anyone else please chime in too, I just picked on Terry because I've found his posts about big brown bats very interesting.

Thank you,
Dave

Dave, is there any bark on this stump? If so has it started to decay? Spruce and pines in general rot quicker when their bark stays on loosely and clinging inviting carpenter ants which move in quickly. The pileated woodpecker comes along and rips the bark off gorging on the ants but the rot damage may have already gone too far at that point. We had two spruces that died in front of our house after they were buried by landfill too high above the trunk. Two years afterward when the trees died, I removed the bark as much as I could reach from one the the two nearly identical trees. The one with the bark remaining rotted quicker and fell. The other lasted another 3-4 years and I finally pushed it down. I think it was because the latter tree could breath and dry out somewhat. Maybe bark left on these dead trees don't protect the tree after it is dead and hasten its downfall. Natural order of things since the birds and other creatures like it this way I'm sure.

Joe

[Dave M]

Joe,
The spruce was healthy when I cut off all the limbs and the top last summer, so it's been less than a year and the bark is still tight. I'm in town so we very rarely have visits by pileated woodpeckers, but we have plenty of all the smaller ones. I haven't noticed any woodpeckers on the spruce yet. Do you remember what the diameter was on your spruce trunks? How long was it between death and the first one coming down? I wonder if I should knock the bark off when it gets loose, how long was it before the bark on yours loosened up?

[Terry Lobdell]

The pictures shown for this design is the same type of box my neighbor just emailed me that he counted 55 big browns exit out of March 22nd!