The release is weather-dependent and depends on the fitness of the bat, too.
Before the release, the animals must be trained for several days after being cured from an injury. The way of live of the animals is important - for example a nyctalus noctula can fly very long distances. Therefore the animals must have a very good physical condition and must be trained very very well. Moreover, their hunting speed is very high, which they must reach in the training, too.
Myotis daubentonii hunt above lakes and rivers, and they need to have a very good condition!
All bats must be able to take off from the ground without any assistance. This is important to survive in the wild! Myotis myotis need to be very quick and it must be easy for them to take off from the ground several times in the trot.
It is important to write down the results of every training-lesson. An animal that can fly well on one day, maybe the next day is no longer fit, perhaps because it had spent the day before all the energy reserves.
The training must always take place in the evening or at night, in order to make use of the activity phase of the animals. Before the training, the animals must have warmed up themselves. When animals are trained during the day or the trainers have not the patience to wait until the bats are really warmed up, the results of the training won’t show you the real condition of the bat. This could unnecessarily delay the release!
Careful preparation of the release
The weather has to be ok, it should not be so stormy, rainy or frosty.
The animals must be returned to the location where they were found. Bats are very social animals, they know their group members. They also know their habitat and hunting areas.
Just before the period of activity (evening) you should arrive with the animals at the location of release. As soon as the wild bats start flying around, you can release the bat. Make sure, that the bat has warmed up itself before taking off! Should no wild bats appear that evening, it is important to check again whether all the above mentioned conditions (weather / location) are right. If not, it is better to cancel the release! If all factors are positive, the animals can be released into the wild, even when no others bats are flying.
Ideally, you check the area of the planned release one or two days before. Then you get to know exactly the flying time and territory of the wild bats.
For nyctalus noctula(s) you better bring a box with an open entrance hole very high (!) into a tree at the location where the bat should be released. The nyctalus noctula(s) should be placed in that box before sunset. Later on the nyctalus noctula(s) will leave the box by itself/themselves. Once all the animals have left the box, the box can be removed. Make sure, that the box is empty!