Bird call in this video...

Can anyone tell me what the bird call in this recording is? I've been hearing it so much lately and it's really nice, I've listened to so many 'common garden bird call' recordings to try to identify it but no luck! The call I'm referring to sounds like a slide whistle going down, with a little "tweet" at the end.

What is this? It sounds so nice.

6052.bird.m4a