From a soundsnap.com article: 5 Most Identifiable (and Overused) Sound Effects in Cinema
The gorgeous eagle that has awed us on-screen is an imposter. Let me explain: that sound that everyone associates with an eagle as it soars into view in a movie? Yeah, it’s actually not an eagle at all. That screech that the sly eagle has been passing off as his legendary call is actually the screech of a red-tailed hawk.
The sound that the eagle actually makes is…well, let’s just say it’s far more adorable and not nearly as impressive as that of the hawk. Which is why it’s been traded for an eagle call in movie scenes; filmmakers have all agreed that it just sounds cooler and goes with the impressive beauty of the soaring eagle. Poor hawk though.