1. Too many (or too few) roosters.
It’s true that you don’t need a rooster to harvest eggs, but a gentleman tends to keep the ladies happier and helps to break up domestic squabbles between the hens. He’ll also alert them to good forage and save it for his ladies to win favor. That said, too many roosters can cause territory disputes and lead to abused hens. A good ratio is one rooster to every 8-12 hens.
2. Inadequate protection from predators.
They don’t say “smart as a fox” for nothing. Predators are intelligent, and if they’re not they don’t make it very long. Chicken owners need to plan in advance to protect their flock. Raccoons have been known to break through mesh chicken wire, or simply reach through and kill birds through the fence. Weasels, believe it or not, can slip through the small holes. Hardware cloth is better to use for a chicken’s overnight housing. They’ll also need protection from digging predators, such as foxes and coyotes, as well as climbing predators such as raccoons, that can carry a hen with them over the fence. Make sure the coop is fully protected top to bottom, and don’t underestimate your predators.