Detection and discrimination of natural calls in masking noise by birds: estimating the active space of a signal

• Published in: Animal behaviour Vol. 65; no. 4; pp. 763 - 777
• Main Authors: Lohr, Bernard, Wright, Timothy F., Dooling, Robert J.
• Format: Journal Article
• Language: English
• Published: Kent Elsevier Ltd 01.04.2003; Elsevier; Harcourt Brace Jovanovich Ltd
• Subjects: Animal behavior; Animal communication; Animal ethology; Aves; Biological and medical sciences; Birds; Ear and associated structures. Auditory pathways and centers. Hearing. Vocal organ. Phonation. Sound production. Echolocation; Fundamental and applied biological sciences. Psychology; Psychology. Psychoanalysis. Psychiatry; Vertebrata; Vertebrates: nervous system and sense organs; Laboratory study; Animal communication; Sound production; Perception threshold; Interspecific comparison; Instrumental conditioning; Background noise; Learning; Vertebrata; Acquisition process; Taeniopygia guttata; Detection threshold; Masking; Aves; Stimulus discrimination; Distance
• DOI: 10.1006/anbe.2003.2093
• ISSN: 0003-3472

We tested the ability of birds to detect and discriminate natural vocal signals in the presence of masking noise using operant conditioning. Masked thresholds were measured for budgerigars, Melopsittacus undulatus, and zebra finches, Taeniopygia guttata, on natural contact calls of budgerigars, zebra finches and canaries, Serinus canaria. Thresholds increased with increasing call bandwidth, the presence of amplitude modulation and high rates of frequency modulation in calls. As expected, detection thresholds increased monotonically with background noise level. Call detection thresholds varied with the spectral shape of noise. Vocal signals were masked predominantly by noise energy in the spectral region of the signals and not by energy at spectral regions remote from the signals. In all cases, thresholds for discrimination between calls of the same species were higher than thresholds for detection of those calls. Our data provide the first opportunity to estimate distances over which specific communication signals may be effective (i.e. their ‘active space’) using masked thresholds for the signals themselves. Our results suggest that measures of peak sound pressure level, combined with the spectrum level of noise within the frequency channel having the greatest signal power relative to background noise, give the most similar results for estimating a signal's maximum communication distance across a variety of sounds. We provide a simple model for estimating likely detection and discrimination distances for the signals tested here. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.