DROPPING THINGS [Ref]
The story is well known, being recorded by Pliny, of how the poet Aeschylus came to his death through a bird mistaking his bald head for a rock and dropping a turtle on it. The bird was evidently the lammergeier or "lamb vulture," one of the largest and most magnificent of the Old World birds of prey; nearly four feet long. In the Atlas Mountains of North Africa its normal food is turtles, and these it cracks open, so that it can get at the meat, by carrying them up into the air and dropping them on a rock. Now it lives in the Himalayas and in Africa, having been almost if not completely exterminated from Europe because of its alleged predation on sheep. Not only turtles but bones are treated in the same manner, to get at the marrow. Though the habit is well known, it is surprising how difficult it is to find a firsthand description of it. So far I know of only one description written by an eyewitness. And yet, in East Africa recently a stony mountaintop was found littered with broken bones that seemed to be the result of the lammergeier's habit.
GULLS DO IT As I have mentioned, gulls open clams and mussels in this way; and crows, which are among the most intelligent of birds, do it also. They pick up the mussels left exposed by the falling tide, fly up above a hard stretch of beach, a big rock, or a stretch of nearby paved road, and drop the shellfish there. While in general this practice is restricted to a few groups of birds, it is practiced by them in many far parts of the world. The Pacific gull of Australia, widely separated from its near relatives, has the same maneuver for opening shellfish as has our herring gull.
It's hard to understand just how this habit came about. One can imagine that some birds found it out by accident when flying about with a stubborn "nut" they were unable to crack. Or perhaps it was in play they found it. The raven is known to fly about carrying and dropping things in play.
SPARROWS DO IT TOO Often, to find a background if not an explanation of a habit, we look about to see if it's used in some other connection. I've already mentioned the play of some of the crows. Only one other "dropping" habit has come to my attention, and that is a single record for the very common house sparrow. Edmund Jaeger writes that in Nebraska, and again in Riverside, California, he saw house sparrows on gravel roofs, dropping small stones over the edge. The pebbles, or small bits of crushed stone, were carried to the edge of the building by the sparrows, dropped, and as each pebble was dropped the sparrow turned its head, apparently the better to watch or listen to the pebble fall and strike. No obvious utility appeared in these actions. It, too, looked like pastime. Perhaps there was no better reason behind them than that behind small children dropping stones down a well.