Birds of Prey: Many Birds of Prey feed on chickens, most notably Hawks and Falcons. Because of this, defending chickens from them is needed especially if you live in places where Birds of Prey flourish

Canids: Coyotes naturally prey on a lot of farm animals such as Cows and Pigs so chickens are their prey. Other Canids such as Foxes and Wolves also prey on Chickens so watch out for them.

Felids: Wild cat species are notorious for eating Chickens and traditional fences may not work to deter them.

This list is incomplete. Please add info if needed

Cats: Chickens may hold their ground against domestic cats and they may get injured while defending themselves.

Dogs: Most Dog breeds don't really do anything with chickens.

Non-Fowl Birds: Silkies are sometimes used to hatch other species' eggs.Broody hens may get injured when Territorial Parents find a chicken hatching their eggs. Chickens may do well with other bird species such as Parrots and Pigeons. Chickens and parrots are both susceptible to PBFD (Psittacine Beak and Feather Disease)

Small Mammals: Most small mammals such as mice and Ferrets are usually kept away from chickens in hamster cages or ferret cages. However ferrets do like to eat whole eggs, raw or cooked.

Rabbits: Chickens and rabbits are perfect for people raising animals in small spaces but Rabbits and Chickens carry diseases that can spread to each other. Rabbits may also seriously injure chickens and even kill them if they become territorial

Ducks: Ducks and chickens go very good together! Having a mixed coop is difficult though, due to the different health and dietary needs for chickens and ducks.

Turkeys: When Raising Turkeys and chickens together, histomoniasis or Blackhead disease, is a concern since Turkeys are susceptible to Blackhead unlike their Chicken counterparts

Peafowl: Like Turkeys, Peafowl are susceptible to histomoniasis and chickens may carry worms and protozoa that spread histomoniasis in their droppings.