COMMUNICATING IN SOCIAL NETWORKS: EFFECTS OF REVERBERATION ON ACOUSTIC INFORMATION TRANSFER IN THREE SPECIES OF BIRDS

Abstract

In socially and acoustically complex environments the auditory system processes sounds that are distorted, attenuated and additionally masked by biotic and abiotic noise. As a result, spectral and temporal alterations of the sounds may affect the transfer of information between signalers and receivers in networks of conspecifics, increasing detection thresholds and interfering with the discrimination and recognition of sound sources. To this day, much concern has been directed toward anthropogenic noise sources and whether they affect the animals' natural territorial and reproductive behavior and ultimately harm the survival of the species. Not much is known, however, about the potentially synergistic effects of environmentally-induced sound degradation, masking from noise and competing sound signals, and what implications these interactions bear for vocally-mediated exchanges in animals. This dissertation describes a series of comparative, psychophysical experiments in controlled laboratory conditions to investigate the impact of reverberation on the perception of a range of artificial sounds and natural vocalizations in the budgerigar, canary, and zebra finch.

Results suggest that even small reverberation effects could be used to gauge different acoustic environments and to locate a sound source but limit the vocally-mediated transfer of important information in social settings, especially when reverberation is paired with noise. Discrimination of similar vocalizations from different individuals is significantly impaired when both reverberation and abiotic noise levels are high, whereas this ability is hardly affected by either of these factors alone. Similarly, high levels of reverberation combined with biotic noise from signaling conspecifics limit the auditory system's ability to parse a complex acoustic scene by segregating signals from multiple individuals. Important interaction effects like these caused by the characteristics of the habitat and species differences in auditory sensitivity therefore can predict whether a given acoustic environment limits communication range or interferes with the detection, discrimination, and recognition of biologically important sounds.