The influence of biotic and abiotic factors on bat activity in Negev Desert, Israel

The effect of biotic factors (vegetation cover and insect abundance) and abiotic factors (ambient temperatures, cloud cover and wind strength) on bat activity was studied during May 2001 in four different sized wadies around Sede Bequer of the Negev Desert in Israel. Anabat detector II was used to detect the activity of bats following both focal and continuous techniques. Horizontal and vertical vegetation covers were estimated at subjective index. Arthropods were counted at four stations within each wadi, temperatures were measured with a thermometer at sampling sites, and cloud cover and wind speed were determined by a subjective index. Even though there is weak relationship between vegetation and bat activity, there seems to be a trend between them. Strong correlation was demonstrated between flying insects and bat activity from the continuous recording (R²=0.92, F-test=22.23, P=0.042) confirming our main predictions but no relationship was found between the focal sampling of bat activity and arthropod abundance. Cloud cover and wind speed did not affect the bat activity but temperature was found to reduce the flight of a flying insect and hence the activity of bats. Our experience from this study reflects the efficacy of using continuous acoustic monitoring over the focal sampling in detecting bat activity.