Tim Birkhead discusses how after an hour of attempting to locate an incubating pair of European nightjars Edmund Selous decided it was better to observe living birds rather than kill them for Smithsonian Magazine:

Selous made empathy for birds respectable and, in doing so, changed the world. Bird-watching became one of the most popular pastimes globally, eventually making birding scientific and playing a pivotal role in the animals’ conservation. Dispassionate killing was gradually displaced in favor of a gentler, more intimate approach whose aim was to better understand the nature of a bird’s world. It was a shift enhanced, naturally, by the appearance of decent binoculars, which in the early 1900s enabled watchers to observe birds from a distance without disturbing them.

As the interest in watching birds rather than shooting them increased, a view espoused by ornithologist Max Nicholson came to dominate the field. Nicholson believed that bird-watching should be “useful,” and he wanted bird-watchers to direct their energies toward an even greater understanding of birds’ behaviors, especially in terms of their numbers—and so started the practice of monitoring bird populations.

Read more to learn about the social hierarchy of birding and birdwatching from the ’40s through the ’80s.