Communication by changing signals: call switching in red-winged blackbirds

Summary

Territorial male red-winged blackbirds use many different “alert” calls which overlap broadly in the context of their use and which are often given in continuous, repetitive fashion. Males give one call type many times before switching to another type, and call during all daily activities. In this field study we demonstrate that males tend to give the same call types as their neighbors and change types to match the changes of their neighbors. Individual males change call types in response to the appearance of a mounted hawk and also match call type changes broadcast from a loudspeaker. The various call types are not associated with particular behavioral contexts. We suggest that red-winged blackbirds operate a general acoustic alert system by calling repetitiously and changing call types when detecting environmental changes such as appearances of predators. Evidence is presented that communication is acheived primarily during switching among different call signals, and not by specific calls that refer to particular stimuli or states of alertness.