Interactions between foraging bats and aquatic insect prey may be influenced by aquatic insect life history characteristics, including the timing of peak emergence, duration of emergence, and adult body size. To examine this relationship, we measured insectivorous bat foraging activity along two Sonoran Desert streams that exhibit contrasting patterns of aquatic insect emergence. Peak aquatic insect emergence from the San Pedro River, Arizona, occurs in April, and occurs over a short time period. Peak emergence from Sycamore Creek, Arizona, occurs in July, and is continuous throughout the summer. We selected 3 reaches (50 m) along each stream. Bat foraging activity was measured monthly at each stream both acoustically and with mist nets (January 2008 – 2009). The timing and duration of aquatic insect emergence was measured using replicate (3) floating emergence traps, and aerial insect abundance was measured using replicate (3) sticky traps. Bat activity and insect abundance was measured directly above the stream and in the floodplain.
Results/Conclusions
The San Pedro River and Sycamore Creek had similar bat species richness (13 and 12, respectively) and abundance (41 and 36, respectively). Along the San Pedro River, bat capture rate was highest April and May (11 and 8 bats per night), declined during the monsoon to 1 bat per night, and increased post monsoon to 6 bats per night. Bat capture rate increased April through July along Sycamore Creek, with a peak bat capture rate of 14 bats per night in July. Bat capture rates were lower in the floodplain of both rivers; throughout the year we captured between 0 to 3 bats per night along the San Pedro River, and none at Sycamore Creek. While overall bat activity was similar in these two desert streams, the timing of peak bat activity occurred earlier along the San Pedro River in comparison to Sycamore Creek. These results suggest that bat foraging activity is influenced by temporal variation in aquatic insect food resources. Alternatively, bat activity and insect availability may be responding to temporal patterns in temperature and precipitation.
