ИСТИНА

Amphibian activity is highly dependent on temperature and humidity. As far as in Asian tropical monsoon forests temperature changes slightly during the year, we may suggest that frog activity must be regulated mostly by precipitation amount; more animals and species should be active during the rainy season (May–October) than during the dry season. To test this suggestion we studied amphibian activity during the whole annual cycle from August 2011 to July 2012 using registration of calling activity and pit-fall traps placed in seven study sites in Cat Tien National park. 2644 individuals of 17 species were found in the traps during 1152 trap-days. The number of catches was highest during the rainy season, however, some species (Occidozyga martensii, Limnonectes sp., Kalophrynus interlineatus) demonstrated high terrestrial activity during the first half of the dry season (November–January). Frog activity reduced greatly in the driest period, in February–March. Adults prevailed in traps in the beginning of rainy season and subadults in the end of this period. The number of calling species positively correlates with the reduction of precipitation in the period August–February. In contrast, the number of calling species grows explosively up to a maximum of 20 registered species with the first heavy rains in April. However, some species, such as tree-hole breeding Theloderma stellatum, keep on calling and reproducing even during dry season. Finally, we distinguish two main ecological groups of terrestrial amphibians: species active all-year round (O. martensii, Limnonectes sp., K. interlineatus), surviving the dry season in small water bodies or in the humid leaf litter, we define them as active patients; frogs active during the rainy season (Caluella guttulata, Kaloula pulchra, Micryletta erythropoda) with explosive growth of terrestrial activity at the onset of heavy rains and surviving the dry period in shelters are defined as aestivates.