What does many a hero did it yield a prey to dogs and vultures mean

Heroes will still die one way or another.

Explanation:

The person that made that statement is Alexander the great.

Alexander the Great is a hero for many reasons. Through his military genius and courage, he united the entire ancient world under one rule. But he did more than just build the greatest empire the world had ever seen, Alexander spread Western philosophy, science and mathematics throughout that empire.

The reason for the statement and the meaning is after your heroic nature on Earth, one will still die one way or the other.