What do I need to know about birds of prey if I keep chickens?
Birds of prey, including
Raptors (who hunt in daylight), and Owls (who hunt at night)
Many different sizes and colors, but raptors are carnivores and generally have sharp talons and strong, curved beaks designed for eating flesh.
Various species are found throughout the world
Unlike the most ground-bound predators of chickens (which may kill many birds or an entire flock at once), raptors will normally only kill one chicken at a time. Due to the predatory birds' long, sharp talons, the chicken killed will appear to have been stabbed with a knife, with many deep wounds and slashes, usually on the back and breast. The breast is often eaten. Owls will sometimes eat the head of your chicken, too.
By contrast, day hunting birds will cleanly pluck feathers. If you find feathers plucked with flesh still clinging to the ends, your bird died of some other cause, and the raptor was just scavenging. Sometimes, however, if the bird of prey is large and your chickens are small bantams or young birds, your chicken may just be carried off to be eaten elsewhere, with nothing remaining.
Birds of prey may defecate near the kill site, stripes or splashes of white. If you have a day hunting bird, for example, you might find feathers plucked and scattered, and then stripes of white wash from defecation on or close to a nearby fence post, tree or telephone pole. Owl defecations will be chunkier, chalkier (and they generally don't pluck feathers).
Many day-hunting raptors are migratory, and especially if you live in an urban area, will usually not stay in the area harassing your flock for long. Anecdotally, we tend to hear more reports of predation by hawks in the spring and fall, perhaps when many of these birds are on the move. If you live in a rural area, though, you may be in the summer or winter hunting grounds of this bird. Even then, chickens are not their preferred prey.
The raptor that most often preys on chickens is probably the Red Tailed Hawk, because it is relatively common for a raptor, and because it is large enough to prey on chickens easily. Bald and golden eagles and other larger birds may prey on your chickens, too. Even very small hawks like the sharp shinned may sometimes try to get one of your chickens, although they normally stick to hunting wild birds the size of sparrows and robins.
Protecting Your Flock
Raptors are not the most common predators in most cases to begin with, so keeping your flock safe from birds of prey is not terribly complex. However, there are a few important things to consider as you decide the most effective way to head off the threat in your particular situation.
First, lock your flock up at night, when owls are hunting. Since they hunt at night, owls preying on chickens that securely cooped will be very rare. For the daytime hunters like hawks, falcons, eagles and the like, you may opt for a covered run. No tall fence will keep out these flying hunters since they attack from the air, so the only way to exclude them is to cover your run with wire or plastic netting. Chicken wire is fine for this, and cheap plastic netting will work equally well. Tying brightly covered ribbon on the cover can help hawks to spot the barrier (otherwise they may dive right through without seeing it, and then get trapped in the run with your chickens!).
If your run is not covered and is very small, your birds have nowhere to run when a hawk comes. If that's the case, they can pile on top of one another in a panic, and trample one another like mobs at Christmas. So, even if the hawk doesn't make a successful kill, if your birds are penned in a small, open run, they may still get very hurt. You will almost always want to cover a very small run for that reason. Many small coops come with covered runs, so you can keep your chickens enclosed during times when there is some lingering danger and you can't be there to supervise.
With larger yards, of course, covering your run can be quite expensive! Plus, your flock is less likely to get hurt or trampled in a panic if they have places to run and hide. So, with a larger run, most people won't want to go to the expense of covering it entirely. In that case, you may choose instead to provide a partially covered run. This gives your chickens a place to hide and take cover from predators attacking from above, but does not provide complete protection. If your chickens don't spot the hawk, they can still be taken by surprise. Even providing a row of bushes for your chickens to hide beneath near the coop offers good help for them in case of flying predators. Birds of prey can't effectively swoop down through branches, and your chickens will (hopefully) still be able to see through them to determine when it's safe to come out again.
Last, if you live in a place where roosters are allowed, roosters are great in helping to keep your chickens aware of dangers from hawks; in fact, they have a specific cry to let the flock know to take cover from an air-borne danger. While the hens are foraging for tasty goodies, the rooster will keep an eye out for danger, and he will place himself in harm's way to give the hens time to escape to safety.
A Special Note:
Do not hunt or trap raptors. They are protected by international treaty. If you hunt or trap them, you could be looking at genuine jail time or humongous, life-crushing fines--sometimes even just for possessing a single feather (and even when you simply found that feather on the ground). Seriously, just do NOT. We can't stress this enough. If you do have a raptor hanging around your coop for a long period of time and your birds are not in a secure, covered run, you can normally call your local agricultural extension office to see if they will relocate it for you, or if they can point you to someone licensed to do so.