Definition of "birdwatcher"

Alec Warner was gazing like a bird-watcher at Charmian, who plucked at the rug round her knees, waiting to tell her own story.

1959, Muriel Spark, chapter 5, in Memento Mori, London: Macmillan

In fact, on this night, the birdwatching is over for everyone, for the firing is cancelled. Nobody notifies birdwatchers officially, of course, so the exodus is scattered and gradual.

1957, Skyline, volumes 15-18, page 7

[…] particularly those carrying astronauts, are the area's major drawing power, and each "advertised" shoot brings thousands of space age "birdwatchers".

1961, Canadian Motorist, page 15