The Rise and Fall of the Dinosaurs by Steve Brusatte is a good introduction to recent dinosaur discoveries.
Mining their own bones for calcium for eggs is another dinosaur trick you find in birds today. Something I didn’t know is that dinosaur (and bird) lungs are quite different from most other types of lungs. We get our oxygen when we inhale. Birds, and their dino forebears, inhale air into their lungs and air sacs; exhaling means a second flood of oxygen through the lungs.
Backyard and Beyond 
Thank you for the the excellent and fascinating information!
There is still a school of thought which sees birds coming from a common basal archosaur ancestor and not from theropod dinosaurs. For a theropod to become a bird several genetic developments, hip structure, forelimb length and heavy cursorial feet, would have had to reverse in violation of Dollo’s rule. And yes, for feathered flight to develop at all, feathers had to precede feathered flight. BTW, the avian respiratory system is a one way path. The inhaled air passes through the lung once, but the advantage is that it exits through a different place than it entered. None of the last breath remains to dilute the oxygen content of the next breath. See works by Sankar Chatterjee or Alan Feduccia for even more fascinating elements of bird anatomy. They don’t agree on al points, but are in unison that flight had to be a trees down process, not the nearly impossible and highly unlikely ground up process implied by thereopod ancestry.
how hard do you suppose is it for birds to mine their bones for calcium?
is there a place to go to die so the bones are easy to find?
They don’t mine them in the way you are thinking. It is a slow dissolution of the calcium in bird bones which makes it’s way to the eggs via their blood stream. Human females do much the same. A pregnant woman who has a calcium poor diet can wind up with very weak and brittle bones. A pregnant woman with a calcium rich diet can be unaffected, or at least not noticably so. I assume the same holds true for birds as well as other animals with skeletons. Chuck McAlexander