The most important thing for you to do when you see an injured or possibly orphaned animal is to get expert advice and help. The best advice will come from a wildlife rehabilitator. Vets and wildlife officers may also be helpful. Remember that all wildlife rehabilitators are volunteers who may also hold full time jobs. Persevere and have patience, for the animal's sake.
Here is some information on what you may need to do to assist an injured raptor- you are responsible for it's survival until it is in the care of a wildlife rehabilitator.
Does it Need Help?
When a raptor is able to be approached, there is something very wrong. Some birds will exhibit little fear of people, but they will not be approachable enough to catch if healthy. Even if the raptor is not obviously injured (ie. bleeding or laying beside a road), it may still be injured or ill.
Orphan raptors may also be fearless, but usually they will only approach people when starving. Nestlings should be put in a substitute nest near an old collapsed one, so that their own parents can continue to raise them. Parent birds do not reject their young if they have been handled- they will even accept them back after a day or more of absence.
If the raptor does need assistance, assess the situation and do only what needs to be done. If possible, contain the bird for it's safety, and so that it does not wander off to die before a carer arrives. An owl that is down and being mobbed by large birds can be assisted by dropping a box over it. A raptor caught in a barbed wire fence can be cut free and put in a box. Additional treatment may not be as straight forward as you think, so refrain from trying to feed it, don't cuddle it, and don't take it to your dog and cat vet without a carer's advice.
Once the initial threat is removed, call a wildlife carer immediately.
Catching a Raptor
If you are able to capture the raptor, you will greatly increase its chances of survival. However, your own safety must be considered first. The best container for the captured raptor is a cardboard box just big enough for the bird to stand in. It should have air holes punched in the sides and a secure lid, with an old towel in the bottom for the raptor to grip. In the absence of a box, a laundry basket or hamper can be used, but it must be completely wrapped up with blankets or sheets. NEVER use wire cages to contain raptors!
Capturing the raptor should be done with care. The major threat to you is the bird's feet and talons, not the beak. If the following approach is used, it is unlikely that you will be injured.
Approach quietly, without staring straight at the bird. Walk the bird into a corner if possible (if they are on a road verge, put yourself between the bird and the road). Have a thick towel draped over your hands, and quickly throw it over the entire bird. Aim especially for the head, so the raptor won't be able to see you. Remember that it will also be able to hear you moving. Once the head is completely covered, you may 'pin' it's body gently but firmly to the ground. You can pause once the towel is over it to take aim, but the pinning has to be done in one decisive move. This will stop it being able to raise it's feet to strike at you in self defence. Beware the raptor that rolls onto it's back - if this happens, you may have to remove the towel and step back until the bird rights itself, then try again.
Keeping one hand pressed on the bird's back, work the other under the body (between the folded wings on large eagles) until you can feel the 'elbows' on the legs. Take a firm hold of both legs. Once they are secure in your grip, gather the bird's wings and body in the other arm and lift it into the waiting box. It is best to remove the towel from the bird's body, but leave it's head covered until you have removed the hand (that was restraining the legs) from the box. Close the lid most of the way, and pull the towel off of it's head so that it can breathe freely. Secure the top of the box.
If you have any doubts about handling a raptor, get assistance. Rehabilitators and DEC Wildlife Officers are experienced animal handlers who may be able to help, usually by giving advice over the phone.
If you are having difficulty locating someone to come get the raptor, and you do not want to handle the injured bird, find a large box and upend it over the bird. Make sure there are lots of air holes, and the box is out of the sun. This will protect the bird and keep it calm. Swimming pool nets can be used to cover or catch smaller raptors. If this isn't possible, leave the bird alone, but keep an eye on it's location until help arrives.
When a rehabilitator can not get to you immediately (remember- all carers are VOLUNTEERS who receive no government assistance), they will still be able to advise you on how to care for the animal until either you or the carer can transport it.