Sound localization in small birds: absolute localization in azimuth.

Area of Science:

• Avian auditory perception
• Bioacoustics
• Animal behavior

Background:

• Sound localization is crucial for avian survival, influencing predator detection and communication.
• Understanding the factors affecting sound localization in birds, such as stimulus complexity and species-specific adaptations, is important.
• Previous research has explored sound localization in birds, but comprehensive studies across different species and stimulus types are limited.

Purpose of the Study:

• To investigate the sound localization abilities of three bird species: budgerigars (Melopsittacus undulatus), canaries (Serinus canarius), and zebra finches (Poephila guttata).
• To determine the minimum resolvable angle (threshold) for various auditory stimuli, including pure tones, noise bands, and species-specific calls.
• To explore the influence of monaural hearing (one ear plugged or deafened) on sound localization performance.

Main Methods:

• An operant conditioning procedure was used to train nine birds from three species to fly towards sound sources for a food reward.
• The angle between two sound sources was systematically varied to determine the threshold for accurate sound localization (75% correct performance).
• Thresholds were measured for pure tones (5 frequencies), noise bands (3 spectral compositions), and species-specific contact/distance calls.

Main Results:

• Sound localization thresholds for all tested stimuli (simple and complex) were consistently larger than 25 degrees across all species.
• Statistically significant differences in sound localization thresholds were observed among the three species for all stimulus sets.
• These species-specific differences in auditory spatial acuity were not correlated with variations in head size.
• Birds with one ear plugged performed comparably to binaural birds, indicating functional redundancy.
• However, birds deafened in one ear performed at chance level, highlighting the critical role of binaural hearing.

Conclusions:

• The study demonstrates that while birds can localize sound sources, their spatial resolution is relatively coarse, with thresholds exceeding 25 degrees.
• Significant interspecies variation exists in sound localization capabilities, independent of head size.
• Binaural hearing is essential for accurate sound localization in birds, as evidenced by the performance of deafened individuals.