Bat House Forum

[marius]

Our friends and family have become oddly curious about bats. Here is a question for which we've not found an answer: Why do some bats sleep in caves in the summer and don't need the sun to warm up? Think I've read that some bat species will not use bat houses. So, are bats like flowers? (i.e. Some species prefer shade and some like sun.)

[William Bagwell]

An overly simplified answer is that bats pick cold caves to hibernate in during the winter and warm caves to rear there young in the summer.

Caves themselves are very complex and while they often have a year round temperature that only varies by a few degrees from the yearly average temperature where the cave is located. Deep vertical caves however can sometimes act as a cold air trap and have a small section that is much colder than than the yearly average. Rarely they even have year round ice. The hibernating bats chose a location that is close to, but just above freezing so they can sleep using the least energy. In some nursery colonies the opposite occurs and the mass of bats will actually raise the local temperature well above average.

And yes, while there is some overlap, some bats will not use artificial roosts and others never visit caves.

William

[marius]

Thanks William. It's kind of what I figured. Still is curious that some bats need to be warmed up in the morning - but maybe no more curious than the fact that some turtles live on water and some on land.

What got me thinking about this is that our big browns do not get any sun on the bat house until 2 in the afternoon and so far they seem fine with this. When I first read about where to hang the bat house, everything I found said a minimum of six hours of sunlight a day. So we hung the house, got bats, and later read that bats prefer MORNING sun. That won't ever happen here because any other place on our house can be accessed by squirrels and I read that squirrels will bother bat houses. We have an abundance of squirrels and they chew on everything - wood picnic table, plastic flower pots ... doesn't matter to them.

[Terry Lobdell]

Marius, I've had a maternity colony of big browns here at home for many years......I would say they definitely do prefer morning sun.........however I also have a west facing insulated box that they use a lot.........early in the spring and later after pups are flying.........

Reason for this preference is in early spring they like a cooler location to stay in torpor (semi-hibernation state) during cold spells when insects are not flying........when it warms up they will roost in east facing boxes........they also like east facing boxes while raising pups for the higher temperatures.....

They again use the west facing box in late summer after pups are grown when high temperatures are not as crucial........

Another time when standard rules about where bats like to roost vary is in late summer when pups start flying.........pups are very curious and explore every crevice they find.........I have had as many as 70 boxes mounted here at home at different times and pups roost in all of them no matter what location........some are even as low as 4 or 5 feet off the ground........

The biggest factor though I think is habitat..........if the habitat is right bats will roost just about anywhere.......

[marius]

Terry - thanks much for all the information. You've given me a lot to consider!

I really do hope habitat is the biggest thing to consider because we have great habitat: stream four blocks away, neighborhood with older trees, farmed areas, fields with cattle - all within 1/2 to 1 mile of us. However, today we have temps around 95 and as you know, our big browns get afternoon sun on their house. I went out with binoculars (7 p.m.) and about ten bats are visible, sort of hanging out of the bat house. One bat has half of her head in the sun, another just her ears. Lots of the bats are opening and closing their wings. As the house does not look that packed with bats, I'm assuming the reason they are hanging out of the house is because it's too hot for them. Guess the silver lining is that I finally got a chance to REALLY look at them but .... if they leave, that lining won't be so silvery anymore.

It they'd use the other house we just put up, I don't think it would be as hot as it will be shaded by a tree in just a bit. Meanwhile, thinking it wouldn't hurt to hang another house (our third) somewhere cooler. Just hope they all come back after they go out tonight. : )

Marius

[Terry Lobdell]

Marius......here is a link to pictures of a bat box with spacers which when mounted on a building allow big browns to roost behind when it gets really hot........my big browns love this design.........I now make all my building mounted bat boxes this way......also have pictures of a chimney mounted box of the same design on this forum......

single-crevice-back-vent-access-house-t425.html

[marius]

Hey Terry,

Thanks for this info! Love your pictures and love that this site lets people post photos. It really helps to understand what folks are talking about. If you look at pics of our bat houses you'll see that our house has trim work that provides "spacers" for the bat houses.
where-and-when-hang-2nd-bat-house-t1103.html

We just measured that space (between back of bat houses and our house) and it's 3/4 inch deep. Is that a good size space for big browns? If not, maybe we'll add spacers to the bat houses this winter.

Our heat index was 107F today. I saw a few bats at the base of the first bat house around 5 a.m. but figured they left because we didn't see bats hanging out of the house this afternoon. So, we checked at 7 p.m. and both houses were completely empty. Guess this means all the pups can fly. Yippee!

And, I would not have thought to check the space BEHIND the bat houses if you'd not mentioned it and what a surprise to see one lone bat ... in the space behind the second bat house!!!!!!

So, wondering if my idea to hang some kind of clinging material to the back of our bat houses is necessary? Ideas?

Thanks again for your help,
Marius

PS I'm kind of sad the bats are gone but relieved to know they aren't too hot wherever they are. : )

[Terry Lobdell]

Marius, do you have an access slot in back of your bat box so bats can move behind it internally?

You could staple some pet mesh (heavy duty vinyl coated screen) on the back with stainless steel staples........or possibly you could just rough up the back...........

It could mean your pups are flying or the mothers may have moved them......

Don't worry.......your bats will be back..........big browns especially move all the time.........

[Erik]

Our friends and family have become oddly curious about bats. Here is a question for which we've not found an answer: Why do some bats sleep in caves in the summer and don't need the sun to warm up? Think I've read that some bat species will not use bat houses. So, are bats like flowers? (i.e. Some species prefer shade and some like sun.)

Hi Marius,
there are a lot of different aspects to the summer roost preference in various bat species. In general bats seek out warm maternity roost (where the pregnant females roost, and have and raise the pups). That is because they can not afford to go in torpor ("daily hibernation") when the roost is too cold, because torpor also slows down the growth of the pup. So a lot of bat species seek out pretty warm roosts, that also stay very warm during the night. Lofts and attics are very popular as a maternity roost, and also crevices in roofs and walls that are very warm. Sometimes it is warm air that is trapped that makes the roost suited and sometimes it is the heat-retaining-capacity of the material of which the roost is build.
Although caves are generally thought as pretty cool on the summer period, just under the roof of big cave the temperature is often higher than on the floor level of the cave. Some caves also trap warm air and it is often those caves that are used by bats.
But even so, sometimes bats are able to have a maternity roost in cool (cold) caves. When there is an abundance of food available bats can sometimes afford to burn a lot of energy all day to keep warm enough. When the numbers of bats get very high they can also warm up the cave....

greetings,

Erik

[marius]

Thanks for more help, Terri and Erik!

We don't have access slots in the back of the bat house but maybe we'll add them this winter. : ) Great idea about what material to add too. Thanks!

Enjoyed hearing more about bats roosting in caves and temperatures there. Was sharing bat stories with girlfriends over lunch today and one friend protested that "Bats DO get in your hair." When she was in high school there was a weekend field trip to Roaring River State Park (in Missouri). All the kids were acting goofy and they were watching bats come out for the night. (I think out of a cave, but not sure.) My friend had very long hair and maybe twisted suddenly which flipped her hair around, but she felt a sudden drag on her hair and indeed, a bat was caught in it. She said she was not upset but now when she hears that bats don't get in your hair it makes her laugh. She has six witnesses to this. Is it true? I've not ever known this friend to spin tall tales. : )

Marius

PS This morning, the one loan bat was again at the back of the new bat house we hung. Maybe it's a male?

[cloudman75]

Thought some would like to see some little browns up close on July 2, 2011. The blue/dark blue house has no ventilation, but was used as a nursery. It faces West but gets some sun all day mounted on a pole.
All the pups are flying now and don't want to leave. It's too hot as the temp here today was 96 degrees F. They have several other houses that are cooler and I suspect the high temps will make them move to a ventilated house. The other photo is my unpainted cedar three chamber and they are also too hot today.
It faces due south and receives a lot of sun, too much it appears even with the ventilation. About half the Little Browns moved in this house when the pups were born in the blue house as it was too crowded. The mothers carried them over before they could fly. They are all flying now.
I counted last night and have a total of 102 bats flying which includes all the pups born this year. My freetail bats left during cold stormy weather the last of April and have not returned. I had about a hundred that left and not one now. The couple of Big Browns that spent a short time with me left when it got hot and I have not seen any lately. The Little Browns can take the heat pretty well.

Uploaded with ImageShack.us

Uploaded with ImageShack.us

Uploaded with ImageShack.us

Frank

[marius]

Now Frank, I very much appreciate those photos! /THANK YOU!

Good to see I'm not the only one who has seen a bat with the sun shining on its head! Something about that visual just seemed "wrong" and that's probably because I've watched too many movies! Also liked the info about which bat houses were used, how much sun they get, ventillation and so forth.

I remember as a kid that sometimes bats roosted in a little redbud tree near where we played. No more than maybe three bats, but they were perfectly shaded all day long. They roosted low, maybe four feet up from the ground. I always thought that was odd, but maybe it wasn't.

[Terry Lobdell]

Marius, in hot weather bats are often found roosting in some odd places.......my big browns especially seek out extra ventilation during hot spells........In late July I get calls every day from people who have bats in their homes.......most of which are pups that have just gotten lost due to their inexperience and seeking out cooler roosting locations.........

[cloudman75]

Uploaded with ImageShack.us Marius, Terry, and others. Terry has always mentioned about bats would use the back of the bat house when it got hot. If you look in the lower left corner you will see the cute little bat head hanging down on the back. This was one smart little bat getting away from the sun and heat in the afternoon. When the sun went down it moved back into the colony.
Terry has it right, some bats use the back when it gets too hot.

Frank

[staceybie]

This year I finally got bats to move in to my bathouse. I believe they are are big browns since I live in southern Ohio. 19 to be exact. As of last Monday they all moved out. Did I understand correctly that they will come back? Where did they go? Why did they leave? Will too much noise made by family and friends make them leave? Or the heat? Or is this normal?