The Specialized Auditory System of Kangaroo Rats

Abstract

This chapter describes the specialized auditory system of kangaroo rats. The combination of their enlarged middle ears, delicately balanced tympano-ossicular system, and cochlear modifications adapt these small rodents for better low-frequency hearing than almost any other very small mammal. The primary predators of kangaroo rats are rattlesnakes and owls, both of which can hunt in total darkness and both of which produce some low-intensity, low-frequency noise while attacking their prey. Normal kangaroo rats can avoid these predatory strikes. Kangaroo rats with experimentally reduced middle ear cannot do so in the dark but can avoid the strikes of rattlesnakes if there is sufficient light. In a study decsribed in the chapter, the kangaroo rats that were blinded could not avoid predatory strikes. Kangaroo rats whose olfactory bulbs were removed showed no caution when near rattlesnakes and were thus more susceptible to predation. The specializations of the middle ear and cochlea of the kangaroo rat facilitate low-frequency sensitivity, which is highly adaptive in predator avoidance. The central auditory pathways and the portions of the cochlea involved in transduction are prominent in kangaroo rats but not specialized. This put extreme selective pressure on modifications such as low-frequency sensitivity that would enable the animals to detect and evade predators that produced some low-frequency noise during strikes.