There are many different predators that will try to harm your chickens including:
Birds of Prey
Dogs, cats, foxes etc.
You can either fence the area around your cages so that they cannot get to them or the ones that can get through a fence can be eliminated by raising the cages off the ground.
Shade netting is an inexpensive way that can be used to keep the chicks inside and the smaller predators out.
You will have to react immediately to ensure the safety of your chickens when an alert for a predator is detected.