Humans are sometimes said to occupy a “pecking order,” but of course the term actually refers to chickens and other poultry. Mild pecking is normal behavior in the flock, employed by dominant birds (or “despots”) as a way to remind subordinates of their lower social position.

But the practice can turn gruesome when thousands of birds are packed wing to wing. Then, some bottom-of-the-order birds are pecked to death — and eaten. As poultry and egg farms increased in size in the 1920s and 1930s, feather-pecking and cannibalism, known in the trade as “pick out,” became serious threats.

In 1939, Joseph Haas, founder of the National Band and Tag Company, devised a fashionable method to deal with cooped-up cannibals: mini sunglasses equipped with red celluloid lenses on a hinged aluminum frame. Poultry farmers were informed that having their chickens see the world through rose-tinted cheaters would “make a sissy of your toughest birds.”

Until relatively recently, the party line among scientists was that cannibalism occurred in only a few species in the wild, like black widow spiders and praying mantises. Cannibalism, researchers felt, was an aberrant behavior resulting from a lack of alternative forms of nutrition or the stresses associated with captive conditions.