Bat House Forum

[cloudman75]

I ran across this formula for estimating bat house capacity. I am not defending it, just passing it on for information. Looks OK to me and I will use it. Also the easiest way I have seen to mount a bat house is by using french cleats as
posted a few times by Terry. Heavier houses would seem to me to be a very good application for french cleats. A company that makes bat houses where I saw this formula furnishes french cleats as an option to mount their houses. Their houses are BCI certified.

Here is the formula: cubic inches of roost space divided by 3 cubic inches = bat house capacity.
An example of the simple math for a 24 inch tall by 12 inch wide house with three baffles of .75 inch spacing would be:

24 " x 12" x (.75 "x3) = 648 cubic inches divided by 3 cubic inches = 216 bats. If you were to have an attic then you would add that cubic inches.


Frank

[Terry Lobdell]

Frank, that is some interesting info.........Did it specify anything different for adults versus a maternity colony with pups?

Here in NWPA, a box like that would provide 6 square feet of roosting area.........(based on usage of only one side of the baffle)

I have a very conservative formula for little browns to avoid over crowding..........

15 mothers per square foot...........

For that box 15 mothers x 6 sq ft equals 90 mother/adults which in my area consistently produce about 45 pups........

My formula gives an estimate of 135 bats total............but like I said, my estimate is very conservative...........

I do know based on experience 25 mothers per square foot leads to pups on the ground..........

I think a box with rough surfaces on both sides of the baffles could hold 216 total bats, but with pups I would be afraid of losing a few to overcrowding...........

Kent Borcherding has said he only finds downed pups under boxes that are overcrowded..........

[cloudman75]

No it did not. I think of it as if you turned a bat house upside down and filled in the spaces between the baffles with bats.
It is based on cubic inches so whether they use one side of the baffle or both was not considered as I see it. Each 3/4
inch baffle space or chamber would hold a certain number of bats. The formula did not even consider what size bats.
I checked it against claims from my store bought OBC three chamber 24"x14" with 3/4 inch chambers.
It appears to me the bat house stores my have inflated claims for number of bats. Maybe I am just too conservative.
After giving it considerable thought, I think an estimate is a waste of time as the bats themselves will determine how many use a particular house. I plan to add more houses if there is overcrowding to the extent I lose pups due to falling from the house. One never knows how many bats will show up until they come. I am speaking from my own experience here and certainly not for others.

Formula used on OBC house.
24"x14"x(3x.75) = 756 cubic inches divided by 3 cubic inches = 252 bats

OBC claims it is good for 300 bats. My little browns always have around 50 or so that leave the three chamber after the pups get some size and start flying. I think a hundred and 50 would be a max number in this house for adults.
Your estimate is more workable for a colony to prevent pups falling. My houses are not overcrowded so I have not experienced falling pups. Thanks for your post as I will modify my use of the formula by dividing by 4 instead of 3 if I build a house this winter. I still have the potato box salvage house to complete which I started months ago.

Frank