This article is from today's New York Times:
When Birds Squawk, Other Species Seem To Listen:
A professor's hunch is that birds are saying much more in warning of
danger than previously suspected, and that other animals have evolved to
understand the signals.
http://www.nytimes.com/2015/05/19/science/decoding-the-cacophony-of-birds-warning-calls.html?emc=edit_th_20150519&nl=todaysheadlines&nlid=68851341&_r=0
