what did legolas shoot at?

[Hot, crispy nice hobbit]

Is this what you guys mean?

"The Winged Messenger!" cried Legolas. "I shot at him with the bow of Galadriel above Sarn Gebir, and I felled him from the sky. He filled us all with fear. What new terror is this?" "One that you cannot slay with arrows," said Gandalf. "You only slew his steed. It was a good deed; but the Rider was soon horsed again. For he was a Nazgul, one of the Nine, who ride now upon winged steeds. Soon their terror will overshadow the last armies of our friends, cutting off the sun...."

Which also brought the question: How many "winged steeds" did Sauron breed? Surely, if there are more than enough of them to re-horse a Nazgul, there would have been enough to horse other of his servants?