Abstract
Oilbirds are active at night, foraging for fruits using keen olfaction and extremely light-sensitive eyes, and echolocate as they leave and return to their cavernous roosts. We recorded the echolocation behaviour of wild oilbirds using a multi-microphone array as they entered and exited their roosts under different natural light conditions. During echolocation, the birds produced click bursts (CBs) lasting less than 10 ms and consisting of a variable number (2–8) of clicks at 2–3 ms intervals. The CBs have a bandwidth of 7–23 kHz at −6 dB from signal peak frequency. We report on two unique characteristics of this avian echolocation system. First, oilbirds reduce both the energy and number of clicks in their CBs under conditions of clear, moonlit skies, compared with dark, moonless nights. Second, we document a frequency mismatch between the reported best frequency of oilbird hearing (approx. 2 kHz) and the bandwidth of their echolocation CBs. This unusual signal-to-sensory system mismatch probably reflects avian constraints on high-frequency hearing but may still allow oilbirds fine-scale, close-range detail resolution at the upper extreme (approx. 10 kHz) of their presumed hearing range. Alternatively, oilbirds, by an as-yet unknown mechanism, are able to hear frequencies higher than currently appreciated.
Highlights
Vision and echolocation allow animals that possess one or both systems to detect and localize objects well beyond their2017 The Authors
We compared echolocation signal design, intensity and emission parameters across conditions, using a minimum of 10 flight sequences per condition and five click bursts (CBs) per sequence (N = 285 CBs, parameters averaged for each bird/flight sequence)
We found no significant differences in the duration of clicks produced by birds in any of the five conditions (ANOVA: F4,52 = 0.84, p = 0.51; figure 2c), but overall CB duration was significantly shorter
Summary
Vision and echolocation allow animals that possess one or both systems to detect and localize objects well beyond their2017 The Authors. Echolocators use three-dimensional auditory localization of objects in their surroundings and update their auditory scene as they move through space [2] with update rates reflected in the rate of signal production [3]. They gauge distance to objects based on the time elapsed between signal emission and echo return and, in laryngeal echolocating bats at least, determine elevation and azimuth from echo spectral cues and inter-aural time and intensity differences [2]. Object detection distance depends on signal intensity and frequency content, frequency sensitivity of the sonar receiver (ear) and the sizes of the objects themselves [4]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
