what is a listening device for Bird Watching?

I want to know why there must be a listening device for bird watching and what is the use of it.

orksecurity8 years ago
"Must"? No. There's no "must" about it. A highly directional microphone is occasionally (rarely) useful if you're trying to pick out the sound of one bird that's too far away and/or masked by background noise, and can be useful if you want to record birdcalls rather than just listen to them.