Among the many things I love about the British is their wacky fondness for animals. And this is just one example. Battery Hens are hens kept to provide cheap eggs. Their lives are nasty brutish and short, as they are killed when they start producing fewer eggs, after really sad lives spent in cages in the dark.
So in tender-hearted Britain there are Battery Hen Rescue organizations, which buy them before they are killed and 'rehome' them. One problem is that many of them have lost their feathers. So, a number of clubs have been knitting sweaters to keep them warm until their feathers regrow. Here is one example I found on YouTube.