I was quoted for the second answer here!
If you can't log on, here's the part I was involved in:
Hey, Wise Guys:
I've read that birds can fly because their bones are hollow, but does that mean they have no bone marrow? And if they don't, how do they produce blood cells?
Joe: Interesting question, Courtney, and one that I hear quite often. It's a common misconception that birds' bones are hollow. They're not hollow in the way that drinking straws are hollow. But birds do have enough space in their bones that their total plumage weighs two to three times what their skeleton weighs. Still, all birds have bone marrow, and that's where their blood cells are formed.
Dan: Don't pretend you knew the answer to that question.
Joe: I did.
Dan: Phony.
Joe: Okay, fine. Some or all of my answer may have been provided by Laura Erickson, science editor at the Cornell Lab of Ornithology in Ithaca, N.Y. That better?
Justin: We actually have a hotline to the Cornell Lab of Ornithology. I think that's the third avian query the folks there have helped us answer.
Joe: Why do we get so many bird questions?
Justin: Because you're a birdbrain.