This paper presents the influence of low - flying military aircrafts during the breeding season on Grey Heron Ardea cinerea colony in natural reserve. The observation results were compared with those conducted in an area of heron colony under going a slight anthropopressure. Aircrafts effect the whole breeding cycle of the heron, which in the light of studies, seems to be most dangerous in the incubation period in which aircrafts disturb incubating and even enable penetration of a heronary by birds of prey, and predatory mammals. In the testing period of nestlings remaining nests aircraft flights were observed to disturb their brooding and feeding and contribute to penetration of predatory animals. They also enhanced premature abandoning nests by fledglings. Over many years these processes resulted in reducing the number of breeding pair of Grey herons in the area located near a military airport.