Contd.
"We show that songbirds adjust the size and shape of their vocal tract to 'fit' the changing frequency of their song," IU neurobiologist Roderick Suthers said. "This enables the bird to produce a more whistle-like, pure-tone song." "...The finding supports a growing consensus that birds and humans make sound in much the same way -- although it is presumed these processes evolved independently of each other in birds and hominids. In 2004, Suthers reported in the journal Current Biology that monk parakeets use their tongues to shape sound. Other studies have implicated beaks, especially beak gape, in shaping the sound that birds produce. Similarly, humans move their tongues, alter the shape of their upper vocal tracts, and change the shape of their mouths when they sing, laugh, talk and groan.
"The bird's vocal tract, like the human vocal tract in speech, acts as a resonance filter that can control the sound coming from the mouth," Suthers said. "
As to birds of carrrion, "American Vultures can smell, but African vultures cannot. The Turkey Vulture has the best sense of smell of the American vultures. Vultures have excellent eyesight, but, like all other birds, they have poor vision in the dark. American vultures find food both with their eyesight and sense of smell. Turkey vultures are attracted to the smell of mercaptan, a gas produced by the beginnings of decay" (Source: Turkey Vulture Society... no, really!).
Thanks for your response!