Bat House Forum

[IowaNate]

So I am looking at some newer designs and I am seeing some houses containing a horizontal roosting area that suppossedly helps when mother bats are giving birth. It would be very easy to incorporate a horizontal "attic" area that is accessable from below as seen in some designs, but does it really help? My mother bats have been having babies on vertical partitions for years and I was wondering if there was any concrete evidence that bats might prefer giving birth on a horizontal plane.

[Erik]

Hi IowaNate,
I must say I have no concrete evidence that bats might prefer horizontal planes for giving birth. But as bats are very able to give birth to their youngsters whilst hanging vertical I don't think the angle of the plane is very important. Horizontal planes get very dirty with bat droppings and urine in which parasites and fungi can thrive. When horizontal is 0 degrees, a vertical slope is 90 degrees. Planes that are >90 degrees are not desired, but I imagine that slopes between 65 and 80 degrees can be very good for bats and their youngster. They still have a very vertical position but also have good grip with their toes as well as their thumbs. In that way a youngster that looses grip of her mother does not fall down but can easily get new grip on the surface it is hanging on / laying on. From experience I know that bat droppings easily stick to a slope of 45-60 degrees. In my large nursery house there is a small slope with this angle and every year I have to remove a thick layer of droppings.
I think that bat moms are more critical about the grip they can get on the surface of the planes or panel. Good grip (grooves/mesh) combined with an almost vertical surface (e.g. 80 degrees) might be the success factor for providing a safe nursery roost.
Does any have experience with bat houses that are designed that way? I have seen drawings of such bat houses.
And did anyone had youngsters repeatedly falling out of the bat house until changes were made to it?

Greetings, Erik

[Terry Lobdell]

Erik,
This is a link to pictures of a bat house where I got a good idea of safe roosting capacity per sqare foot this past summer. The first bat house shown had an exit count of 74 little browns June 5th of 2008. Given the box only had about 3 square feet of roosting area I knew it was too crowded with approx. 25 bats per square foot. We soon put up the 2nd box also shown in this link. Unfortunately, we still lost 5 pups due to falling before they were acclimated to the new much larger box. my guess for little browns is numbers greater than 15 mothers per square foot is too crowded.
I have some slanted baffle boxes (75 degrees) which were used by some of my big brown mothers this summer. They were not used extensively though, I think possibly due to some morning shading from trees.
Kent says falling pups is always due to crowding and I would have to agree with him.

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