A lot of people ask about the ethics of eating endangered animals. Eating endangered livestock encourages farmers to raise endangered breeds and this is the only effective way to prevent the extinction of the breeds. Chickens can’t be released into the wild and most zoos aren’t interested in raising chickens for exhibit. Chickens are farm animals, but farms have to make a profit or they go out of business. Therefore, farm livestock have to be sold.
When raising endangered livestock, farmers keep the best of the breed for breeding more and better animals and sell off the culls or the animals that aren’t perfect (e.g. a Dorking with four toes instead of five would be a cull). The culls are the ones that get eaten. This practice keeps the breed strong and healthy just as what would happen naturally in the wild. Any animal in the wild who isn't strong enough to survive gets eaten.
Read this great New York Times article:
An Unlikely Way to Save a Species: Serve It for Dinner