A chickadee with a leg band. 
CNN Today in a Reuter’s story about the calls of Chickadees…and what they mean
“If you ever go out and are hearing a chickadee making a really long string of “D” notes on a call — six or eight or even 10 — you know there is a really dangerous predator around, maybe the next-door neighbor’s cat or an owl or a fox,” Templeton said in a telephone interview.
“It is very strongly correlated with predator body size.”
And with chickadees, smaller equals more dangerous, Templeton wrote in a report published in Friday’s issue of the journal Science.
“The only predators that can really catch chickadees are the ones closest to them in size,” Templeton said.
Captive chickadees reacted strongly when shown a pygmy owl, for instance, but their calls communicated less alarm when they saw a larger raptor.
The social birds often mob a predator to drive it away.
When recordings were played back to chickadees, they showed “mobbing” behavior appropriate to the predator that the recorded bird had been seeing, Templeton said.
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