The cave Ajdovska jama is one of the rare examples of larger caves in the area of isolated karst within the Krško hills region. It is placed on the steep slope of the karst enclosed valley Podjama (Kartušev dol). The cave is a 62 m long horizontal dry cave with two entrances. The left entrance is located approximately four meters higher than the right entrance.
The left entryway opens up to a ten meters long and four to six meters wide corridor with two side tunnels. This corridor continues to a six meters long and five to eight meters wide passageway, which leads to a spacious central funnel-shaped hall. Its high vaulted ceiling is segmented into several bell-shaped structures or chimneys, formed by corrosion, while the walls feature only partial sintering. Due to various rockslides, the original form of the hall has thoroughly changed through time. The central hall is connected also with the right corridor, which is twenty meters long and two to three meters wide and winds steeply downward towards the right entrance.
Characteristic of the Krško hills region are karst enclosed valleys, similar in appearance to the karst depressions or the so-called uvalas, which contain a subterranean watercourse and feature a levelled bottom together with even, relatively high perimeter edges. One of the more explicit examples of such a karst enclosed valley is precisely Podjama, known also as Kartušev dol. It has been created through interchangeable processes of karstification, tectonics and caved-in surfaces. The enclosed valley is of irregular shape with three branch-like valley extensions, whereas its central part, below the cave Ajdovska jama, measures approximately 300 m in length and 200 m in width. The bottom of the valley is composed of thick deposits of Holocene-age sediments of red-brown and grey clay. The valley formed within the Upper Cretaceous limestone layers, which towards the surface pass into layers similar to flysch deposits. Towards the northwest, the valley transforms into a narrower depression, which contains two springs on its edge slopes. Both watercourses merge together on the valley bottom, where a stream flows along its eastern part to the sinkhole, located at the lower southern end of the enclosed valley. The stream is characterized by a shallow bed, composed of sandy sediments and stones, and by various small side river branches.
Towards the north, the enclosed karst valley ends with a steep slope above the Ajdovska jama, while beneath the cave there is an intermittent karst spring. The spring occasionally discharges water, which flows above ground for only about 100 meters only to disappear again to the underground, where most probably runs further towards the sinkhole at the southern end of the enclosed valley. This watercourse then flows underground from Podjama all the way to the Srednik spring, located under the Brezovska Gora some 600 m away.
The cave was formed in the Upper Cretaceous layers of flat grey limestone. It was shaped by the water current which shifted in time into depths, due to the processes of karstification. During the heavy rainfalls, this water current discharges out from the karst spring, located under the right entrance of the cave. After the conclusion of hydrological activities, the cave was further shaped by rockslides and the corrosion, caused by the percolation water. Floors of both cave entrance corridors are covered with rubble, while the bottom of the central hall is filled with a thick layer of clay.
As far as the water fauna is concerned, we should emphasize the area of two narrow valley extensions with a permanent watercourse on surface, where the presence of the stone crayfish (Austropotamobius torrentium) has been confirmed.
The cave Ajdovska jama is also a significant regional refuge for bats. Throughout the summer season the cave has favourable temperatures, which rise to 21 °C under the ceiling, and is consequently used as a habitat for two large bat maternity colonies – up to 350 female specimens of the Mediterranean horseshoe bat and up to 270 female specimens of the Geoffroy’s bat roost here every year. The cave is also home to up to 100 specimens of the common bent-wing bat species.
It should be mentioned as well that cave bear bones of rare extinct species, Ursus ladinicus, have been found in the Pleistocene sediments of Ajdovska jama, what most probably indicates that this bear species had a den in the cave as early as over 40,000 years ago.
In terms of water fauna, the importance lies in both arms with permanent water, as the presence of the stone crayfish (Austropotamobius torrentium) in it has been confirmed.
Ajdovska Cave is a regionally significant bat shelter. In the summer season and due to favorable temperatures which rise to 21 °C under the ceiling, the cave is a roost for two large clusters: up to 350 females of the south horseshoe bat and up to 270 females of Geoffroy’s bat. The cave is also home to up to 100 common bent-wing bats.
It bears noting that bones of a rare species of cave bear – Ursus Ladicinus – have been found in the Pleistocene sediments of Ajdovska Cave, indicating that it housed the aforementioned bear as early as over 40,000 years ago.
In the central hall of the cave the ground is covered with large amounts of guano.
After the World War II, the locals regularly visited Ajdovska jama to collect bat droppings or guano in order to use it for the fertilization of their fields. Guano is an exceptionally effective fertilizer as it contains three main elements, crucial for the plant growth – nitrogen, phosphorus and potassium.
CAVE IN THE WINTER PERIOD
In the winter, when temperatures in the cave can sometimes fall below the freezing point, only a small number of bat specimens stay to roost in the ceiling chimneys, among them the species of the lesser horseshoe bat, the greater horseshoe bat and the western barbastelle bat.