Eavesdropping

Eavesdropping songbirds get predator intel from overheard calls
from here (and for the full article)

Humans are a funny lot. While we seem to be relentless voyeurs, we generally frown on eavesdropping as an invasion of privacy. But in the animal world, eavesdropping can be a matter of life or death. Animals rarely communicate in isolation. Often it pays for one species to monitor the dialogues of others, particularly when predator warnings are involved.

Small animals in particular do well to pay attention to the alarms of other species, as they are often preyed upon by the same larger hunters. Even very unrelated species can listen in and understand each other's signals. Vervet monkeys respond to the alarm calls of superb starlings, while mongooses are well-versed in hornbill calls...

Alarm calls aren't just a simple matter of shouting "Look out!", and many species have different calls for different predators. But one of the most sophisticated alarm systems so far discovered is used by a small, unassuming bird called the black-capped chickadee.

The chickadee acts as an inadvertent sentry for a multitude of bird species. Its name comes from its distinctive "chick-a-dee" alarm call, made in response to a perched bird of prey or a land predator. When this call sounds out, anywhere between 24 and 50 species of bird marshall together and mob the predator, robbing it of the element of surprise and harassing it from the area.
---

Nice to know.