The scene may have been staged, but Wiki's entry on them suggests the demonstrated behavior is completely authentic, instead taking a more semantic argument about the term suicide: --- "Lemmings have become the subject of a widely popular misconception that they are driven to commit mass suicide when they migrate by jumping off cliffs. It is not a deliberate mass suicide, in which animals voluntarily choose to die, b…
Or find a way to watch that segment of the documentary. Those few lines of the narration don't really capture the narrative of the visual story-telling. (Though it was somewhat sickening to watch even before we knew the filmmakers were torturing and killing the lemmings rather than just observing them.)