Nosy Rodents?

Nearly everybody is guilty of eavesdropping once in a while; it often comes naturally to listen in on the conversations of people around you- especially if the subject matter is something that affects you. According to Joseph Felts and Kenneth A. Schmidt, other animals also pick up on signals that are not meant for them to hear. In the paper "Multitasking and eavesdropping in cotton rats foraging under predation risk," Felts and Schmidt describe the way that cotton rats use signals from other animals to determine when predators are nearby.

Red-tailed hawks are a common predator of cotton rats. They also hunt small birds living in the area including blue jays and robins. Felts and Schmidt predicted that cotton rats would use signals from these birds to determine whether there was danger of a hawk attack. They tested the response of cotton rats to the alarm call of the blue jay, the nonalarm vocalization of the blue jay, Robin song and the call of the red-tailed hawk itself. To test the rats' perception of danger, they used the concept of giving up densities (GUDs). Cotton rats (and other foraging animals) maximize their energy intake by balancing the amount of time they spend foraging in an area with the costs and risks of foraging. When food becomes scarce enough that the energy gained from foraging is equal to the costs and risks associated with foraging, the behavior stops. GUDs were measured by providing the rats with seeds mixed in sand and measuring the amount of seed that was left by the rats. Felts and Schmidt predicted that the GUDs of cotton rats would increase when they heard the alarm call of the blue jay or the call of the hawk itself and that GUDs would decrease when they heard the nonalarm song of the blue jay or the robin song because these songs indicate that there are no predators present.

Felts and Schmidt found that while cotton rats did not respond change their behavior(significantly) in response to the nonalarm calls of the blue jays or robins or the call of the red-tailed hawk, they did respond to the alarm call of the blue jay. When they heard the blue-jay alarm call, the GUDs of cotton rats increased and they spent less time foraging. I thought it was really interesting that animals not only develop signals to communicate with each other, but can also evolve to respond to other signals that benefit them.