Data from: Oilbirds produce echolocation signals beyond their best hearing range and adjust signal design to natural light conditions

Oilbirds are active at night, foraging for palm fruits using keen olfaction and extremely light-sensitive eyes, but use echolocation as they leave and return to their cavernous roosts. We recorded the echolocation behavior of wild oilbirds using a multi-microphone array as they entered and exited their roosts under different natural light conditions. We report on two unique characteristics of this avian echolocation system. First, oilbirds reduce the energy and number of subunits in their otherwise stereotyped echolocation signals under clear full moonlight conditions, but do not reduce their signal emission rate under these same conditions. Second, we document a frequency mismatch between the reported best frequency range of oilbird hearing and these signals’ range (~2kHz) of maximum energy (7-23kHz). This unusual signal-to-sensory system mismatch likely reflects avian constraints on high-frequency hearing but may still allow oilbirds finer-scale, close-range detail resolution at the upper extreme of their presumed hearing range. Alternatively, oilbirds, by an as yet unknown mechanism, are able to hear frequencies higher than is currently appreciated.