Hearing sensitivity and critical ratios of hooded crows (Corvus corone cornix)

The hearing threshold and critical ratios were estimated psycho-acoustically for captive wild-caught hooded crows by a yes/no procedure and the method of constant stimuli. Human subjects were tested in the same setup for direct comparison and to check for experimental artifacts. The hooded crows were found to have excellent low-frequency hearing capabilities compared to other passerine birds. Their hearing sensitivity is very close to that of humans at and below 5.6 kHz. The distribution of the critical ratios differed from that of the average bird and humans in being rather constant with frequency and not increasing monotonically. It furthermore showed a middle region of 5-6 dB lower critical ratio values between 500 Hz and 2 kHz. It is suggested that this improved range for hearing in noise is an adaptation to long distance communication. Human critical ratios gave the expected values and were between 3 and 6 dB lower than those of the crows.