The little shrieking sounds in Canthan outposts

In some Canthan outposts, like Vizunnah Square, you can occasionally hear strange shrieking noises in the distance. Does anyone know what that is supposed to be? I'm contemplating between some birds or afflicted people.

In Guild Wars, they could be huge frickin' monsters for all you know.
My best guess is some sort of bird though.

rats maybe? they do have the critters walking around.

Pretty creepy. Same kind of noised can be heard in any Kurzick outpost, although those are sounding more birdlike. There are definitely some ravens there.