Summer microhabitat use and diel activity cycles in a high altitude Pyrenean population of Rana temporaria

Habitat use and activity was studied in a common frog (Rana temporaria) pop ulation at an altitude of 2200 m in the Circo de Piedrafita, Spain, was stu died during July 1998. Adult and juvenile frogs clearly selected moist micr ohabitats, and avoided dry substrates such as pasture and rocks. Marshes an d puddles were the preferred microhabitat of both adults and juveniles; the shore and the water body itself of a larger pond were selected by adults b ut much less so by juveniles. Regular surveys over seven days indicated tha t adults showed both diurnal and nocturnal activity, whereas juveniles were more strictly diurnal. The percentage of adults observed at night in the p ond was negatively correlated with the minimum air temperature. The rather aquatic habits and diurnal activity patterns appear to differ from low-alti tude populations of R. temporaria. They are discussed as adaptations to the lack of humid substrates (forest leaf litter) at high altitudes, and to th e extreme and unpredictable climatic conditions (low nocturnal temperatures , and sudden rapid temperature decreases at night) in montane environments.