1) Animal communication 2) Audubon recording 3) Avian sound 4) Call 5) Producer of some trills 6) TWEET 7) Whistle of a sort 8) Whistle or trill 1) Birdsong 2) Note 
• (n.) An instrument of any kind, as a whistle, used in making the sound of a birdcall. • (n.) A sound made in imitation of the note or cry of a bird for the purpose of decoying the bird or its mate.
Bird'call` noun 1. A sound made in imitation of the note or cry of a bird for the purpose of decoying the bird or its mate. 2. An instrument of any kind, as a whistle, used in making the sound of a birdcall. 
[n] - the characteristic sound produced by a bird 2. [n] - a device for imitating a birdcall
call 3 birdsong noun the characteristic sound produced by a bird; `a bird will not learn its song unless it hears it at an early age`