You might be surprised to learn that tufted titmice use alarm calls to warn others that predators are nearby. Surprisingly vocalizations reveal to others both the size of the predator and the degree of threat it poses.
In experiments using models of predators ranging in size from the eastern screech owl to the red-tailed hawk, biologists found that tufted titmice reacted differently to models of different sizes. The alarm calls voiced when faced with the presence of models of eastern screech owls were longer and contained more notes, than those made when provoked with models of much larger predators such as the red-tailed hawk. Titmice also mobbed the eastern screech owl models longer than the red-tailed hawk. In addition, the birds also waited longer before resuming feeding activities than they did after dealing with models of larger predators such as red-tailed hawks.
The researchers surmised this was because smaller eastern screech owls pose less of a threat to them than red-tailed hawks.