Abstract:
Laboratory characterization of auditory sensitivity in wild vertebrates is typically based on measurements from a small number of relatively healthy and young individuals. The auditory sensitivities of animals in populations are likely to vary greatly; individuals will vary in sensitivity at birth, and will experience diminished capacity due to injuries, noise exposure, age, starvation, reproductive stresses, parasites, etc. Although disabilities might be fatal for hearing-dependent species, such as nocturnal animals, healthy individuals with profound loss are sometimes found. Hypotheses about the adaptive value of hearing cannot be addressed without techniques to measure animal hearing quickly and accurately in field situations. While conditioning (``behavioral'') studies are the ``gold standard'' against which other techniques are evaluated, they cannot be used easily in the field. Examples of other techniques will be given and compared with behavioral measures for the same or similar species. These are (1) reflex modification (startle inhibition) used on 4 kit foxes (Vulpes macrotis) and 4 Merriam's kangaroo rats (Dipodomys merriami), (2) auditory brain-stem responses used on 16 kangaroo rats and 12 desert tortoises (Gopherus agassizii), and (3) envelope-following responses used on a desert tortoise and a harbor seal (Phoca vitulina).