The Acoustic Search In the field ARU mounted on a tree (left)
with its battery (right). Photo by Chris Tessaglia-Hymes To
search for acoustic evidence for Ivory-billed Woodpeckers in
Arkansas and other states within the historical range, we record
ambient sounds using autonomous recording units (ARUs). ARUs are
programmable, battery-operated digital audio recorders developed
by the Cornell Lab of Ornithology’s Bioacoustics Research
Program. Each ARU contains a microprocessor, 12-bit analog-to-
digital converter, an omnidirectional microphone, preamplifier
and signal conditioning circuitry, and a hard disk for storing
audio data. These components are packaged in a cylindrical PVC
housing, and attached to tree trunks two to three meters above
the ground or water surface. ARUs are typically deployed for
periods of two to four weeks. ARU in Arkansas. Photo by Chris
Tessaglia-Hymes ARUs are programmed to record for two four-hour
periods each day, the first beginning 30 to 45 minutes before
sunrise, the second endin