O. G. Dely szerk.: Vertebrata Hungarica 8/1-2. (Budapest, 1966)

Topál, Gy.: Some observations on the nocturnal activity of bats in Hungary 139-166. o.

mum of the curves display the activity of the individuals. One might infer that the departure of Rh. euryal

e specimens - maybe depending on the individual numbers of the population - took about an entire hour of time. The actograms of the beginning of August give a more uniform picture, except for the evening of 1 August, 1959, wherein the sharp division of the curve was on this occasion caused by the frequent flashes of the photographic camera used on this occasion. To be more precise, this species was less sensitive, while the others, especially Hyotis myoti

s, had first retired from the light and then appeared in masses. In the Görömbölytapolca Cave, the bats behaved on the occasion of the single evening observation entirely similarly to those of the Pisznice Cave, After the departure of the adult animals, I found the juvenile ones hanging densely in an area of about 2 m2. It is to be noted, however, that some returning adults could be seen towards midnight.Unfortunately, I had then to abandon further observation. The series of observation in the Baradla Cave is rather intermittent. Work was here made difficult by the fact that, as was found proven in 1965, the bats communicated through at least two openings. With reference to the period elapsing between sunset and the commencement of departure of the bats, there is a difference between the behaviour of the populations of the Pisznice and Görömbölytapolca Caves and that of the Baradla Cave. While the exit of the species from the Pisznice Cave starts between one minute before sunset and 27 minutes after it, the first Rh. euryal

e specimens fly out of the Baradla Cave 28-40 minutes after sunset (see Table l). This difference cannot be explained on the basis of our present data. Studying the Table, one might think at first that the time of sunset probably plays no role on the commencement of departure, since the period elapsed in the meantime had been considerably different. However, on days when we have de-