"The Adventure of the Avian Eavesdroppers."

This is a fascinating story of two species who “talk” to one another.
Eavesdropping Nuthatches Appear To Understand Chickadees In Distress

"No one has ever seen this behavior before. There are a fair number of animals that respond to other animal's alarm calls. But this is the first example of subtle information from a call being interpreted by another species," said Templeton. "Nuthatches can tell if a raptor poses a high or low danger from the chickadee's alarm call."

I’ve witnessed blue jays and crows as they seemingly cry, “To arms! To arms!” upon spotting a hawk or owl in the trees. Every jay and crow in the immediate area rushes to the source. It usually results in the harassment of that predator until it is well on its way. This research, however, shows a much more subtle communication. I wonder if it is a learned behavior or if the nuthatches have an innate sense of what the chickadees are broadcasting.