In terms of loudness, bats send out calls as low as 50 dB and also as high as 120 dB, which is louder than a smoke detector 10 centimeters from your ear. The Little brown bat (Myotis lucifugus) can release such an extreme sound. Fortunately is that because this phone call has an ultrasonic frequency, we are unable to hear it. So "real" milk-producing mammary glands are special to mammals.
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