Heffner, Henry; Heffner, Rickye (January 2007). "Hearing Ranges of Laboratory Animals". Journal of the American Association for Laboratory Animal Science. 46 (1): 20–2. PMID17203911. Retrieved 19 September 2014.
Heffner, Henry; Heffner, Rickye (January 2007). "Hearing Ranges of Laboratory Animals". Journal of the American Association for Laboratory Animal Science. 46 (1): 20–2. PMID17203911. Retrieved 19 September 2014.