I don't know about bat houses. These bats chose this location.
They have been here for around 20 years or so. Females live 10 years,
so it must be their offspring that returns, after a few years anyway.
These bats have been reclassified as Perimyotis subflavus, which I
certainly agree with based on their behavior and size. It is not often
the maternity colonies are even seen.
Unfortunately for the bats and for us, a fungal disease commonly called
white nose syndrome is causing bats to die, and it is spreading. It was
first noted in New York, I think in 2006.
When they arrive in the spring, I will check, and if any evidence of the
disease is present, I will report it. So far, they have been fat, with shiny
healthy looking fur.
Most of the time, they have twins. Other bats have only one babe.
They are used to us, and the noise from the lawn tractor, something that
concerned me years ago when they first arrived. I didn't want to disturb them.
They have a good sleep, and leave around eight o'clock to feed.
They stay for several weeks. Once the babies mature, they leave.
