Bat Behaviour

[RoPey]

Hi all
For the last four years we have had bats roosting in the apex of our roof over the period when they have their babies, but they only stay for about two or three weeks. The really odd thing is that for two of those years on the very day after the night that they leave us we've found a dead baby bat on the ground near the roost.
Could anyone shed some light on why they stay such a short time and possibly the presence of a dead baby on two of the occasions. I wonder whether the baby is just a casualty of the departure.
Any info would be very greatly appreciated.

[Wild-Woman]

Hi RoPey and welcome to WAB. I'll ask at my next bat meeting about the dead baby but I'm sure that you're right about the bats departing the roost and it sadly just becomes a victim of the rush outwards. They do lose grip sometimes.
Good th hear about your maternity roost anyway. Lucky you. ww

[RoPey]

Thanks for the welcome and the reply Wild Woman. Is that what this is then - a maternity roost? Is there a reason that they do this rather than using a roost all year round?
I don't even know what type of bat they are, but I do love to watch them in the evenings, there appear to be quite a lot of them - judging by the amount that come out without any going back in, and the amount of bat poo on my patio every morning! ;-)

[Wild-Woman]

I would think they are Pipistrelle bats, if they are about sparrow sized.
Our pips follow a certain pattern I've noticed when leaving they're roost in the trees. They start off with small fluttering arc, then small circles which are ever increasing before they break off and hunt for small insects.
Pips are the most commonest to be found in houses. It may be a good idea to let your local bat group know because they generally keep records which enables them to keep an eye on populations and to learn whether there is a dip/increase. Early warning signs are valuable if there is a sudden drop off of numbers. They will also give you practical advice and help if you ever needed to do, say roof repairs etc. They are delightful creatures and the poo makes excellent plant food!ww

[henrya]

Although some maternity roosts are used for long periods during the summer, some species, particularly the pipistrelle, like to move around. The chances are that 'your' bats are not very far away, perhaps even in your neighbours roof. Why they move is not known for certain - but some moves are triggered by weather conditions.

Nobody knows much about where pipistrelles go in winter (in Britain) - it's only in the summer when the females gather together in their maternity roosts that they are at all easy to find.

The dead baby may be one whose mother had been killed.

henrya

[Jo Pedder]

There are several reasons why bats move between roosts through the year.

In winter bats go into torpor and hibernate. In order to do this they need to expend as little energy as they can and they reduce their heart rate and body temperature as keeping themselves warm costs a lot of energy and during winter there is not much food to replenish that lost energy. So in winter, bats seeks roosts that will have stable low temperatures of about 1-6 degrees (roughly fridge temp) such as hollows in very big trees, cellars, caves etc. your roof will obviously not provide these requirements in winter.

In summer their needs change, particularly for pregnant bats who want to find roosts as warm as possible to increase the rate at which their young grow. At this time males normally roost on their own, and females gather together in warm roosts (such as south or eastern aspects of buildings) and share body heat. They would probably benefit if they stayed at these roosts through spring and autumn as well, but they would increase the risk of building up parasites at the roost site. Using the maternity roost for birthing and weaning pups exclusively may help them retain a viable maternity roost to return to year on year.

Not sure about the causes of your dead pups, like most animals I'd expect that some of the young wouldn't survive their first year, the bodies may even be deliberately ejected by adults to keep the roost clean, but that's just guessing.

Hope this helps, Jo

[nightshade]

Hi roPey,if you can send the pups bodies to the Bat Conservation Trust http://www.bats.org.uk/ they will be able to tell what happened,whether it was disease,or perhaps congenital,with so few bats around they do need to know

[henrya]

RoPey,

I should email or telephone the Bat Conservation Trust to check that they actually want bodies before you send one, if I were you! There website doesn't suggest that they have facilities for doing post-mortems (that I can see, anyway).

henrya

[RoPey]

Originally Posted by Wild-Woman

It may be a good idea to let your local bat group know because they generally keep records which enables them to keep an eye on populations and to learn whether there is a dip/increase. Early warning signs are valuable if there is a sudden drop off of numbers. They will also give you practical advice and help if you ever needed to do, say roof repairs etc. They are delightful creatures and the poo makes excellent plant food!ww

Thanks for the info WW, I will try to find out who/where they are. It seems like we are now a regular place for them to come.
I wish I'd known that about the plant food before, I've been hosing off the patio every morning to stop the dog picking it all up. Ah well - hopefully next year...

Thanks again

[RoPey]

Thanks henrya and Jo, really really interesting to read all that - I don't know why I haven't thought to find a forum like this before.
I'm sure they are still around somewhere close because we still see bats fly around the house at night, just not out of our roof, and the poo and grating noise during the day have gone. The apex of the roof that they roost in is south south west facing so very warm through the afternoon and evening. We live on a non-working farm (rapidly becoming an industrial estate) and so there are lots of buildings around for them to move to.
As to the dead ones, I suppose there is always an infant mortality rate, but it just seems so odd that on the two occasions we've found them it has been the day that we notice they've gone.
If it happens again I will contact the Bat Conservation Trust and see if they want to little body. I'm afraid I buried this little chap pronto before a nosey canine pup got too interested.

Thanks to all for such interesting replies - if anyone has anything else to add I'm still fascinated to learn more.

RoPey