Temporal variability in insectivorous bat activity along two desert streams with contrasting patterns of prey availability

Emergent aquatic insects provide significant resources for terrestrial consumers. The availability and consumption of aquatic insects by terrestrial consumers may be influenced by characteristics of the river and riparian area. We measured temporal variability in bat activity and insect availability along two desert streams of contrasting productivity, hydrology, and riparian vegetation in Arizona, USA. Sycamore Creek is very productive, winter storm dominated, and supports sparse riparian vegetation. San Pedro River productivity is low, most floods occur during the summer monsoon, and it has extensive riparian vegetation. Bat activity and insect availability were measured monthly directly above the stream and in the floodplain for one year. At Sycamore Creek, emergent aquatic-insect biomass peaked in spring, while terrestrial-insect biomass was highest in the summer. Aquatic and terrestrial insect availability at the San Pedro River were similar or dominated by terrestrial insects throughout the spring and summer. Interactions between bats and insects differed between these two streams and this variation appears to be due to differences in insect availability in the airspace above the stream. Insect-prey availability is linked to stream productivity, timing of flooding, and the extent of riparian vegetation, and these factors can have strong effects on terrestrial food webs.