How 'natural' are nature documentaries?

The signature scene in the Oscar-winning 1958 Disney documentary “White Wilderness” features a mass suicide of lemmings. That scene was disturbing for the faint of heart, but that’s not why the film is now infamous. It turned out the whole thing was staged and the lemmings did not voluntarily jump to their deaths – they were pushed to their deaths by the film crew. Filmmakers have gotten better about not engaging in outright animal cruelty these days, but nature documentaries still fake quite a lot, like adding sound effects in post-production. Are filmmakers being dishonest or is a certain amount of fakery to be expected?