The acuity of echolocation in Collocalia vanikorensis granti was studied by measuring the success of freshly captured birds in avoiding cylindrical obstacles in total darkness. The percentage of misses varied from approximately 40% with 2 millimeter insulated wires to 80% with 6.3 millimeter iron rods and 68% with 8 millimeter plastic tubing. The orientation sounds used for echolocation are clicks with the major energy between 4.5 and 7.5 kHz. Although the frequency range of hearing in these birds has not yet been measured, it seems probable that they can echolocate obstacles as small as 6 millimeter diameter rods by means of frequencies within the range of human hearing.
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Griffin et al. (1970) studied this question.
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