Most researchers are outside in the daylight, when they can see birds actively hunting insects. Bats, however, hunt insects at night, which is inherently more secretive and harder to observe, said Sunshine Van Bael, a Smithsonian researcher involved in earlier exclosure projects.
Kalka speculates that the documented greater effect of bats as insect predators in Panama could be attributed to the absence of migratory birds in the area during the study period. This explanation is supported by a similar study presented by researchers from the University of Michigan in the same issue of Science. There, the authors report a seasonal shift in top-down effects of bats and birds on herbivory of shade-grown coffee plants in Mexico. Birds are more important insect predators in the dry season, when migratory birds are present, but are less important than bats in the rainy season, when migrants are absent.
It is clear from both studies that bats play an extremely important role in the food chain in the tropics and probably in temperate areas as well. Bats should be considered in both conservation planning and in management strategies for agricultural areas.
|Contact: Beth King|
Smithsonian Tropical Research Institute