Here is an overview of the types of housing a raptor carer needs, if they are planning to care for the birds through the whole process. Because these birds are so reliant on their fitness to be able to catch prey, pre release conditioning is very important. Of course, not everybody can fit a 30 meter (100 foot) pen in the back yard, so many carers cooperate so that large aviaries are shared.
Building Materials and Construction
The major points to remember are that there should not be anything sharp, like the ends of nails or staples. All the wood or steel used must have soft rounded edges, with no splinters. Wire mesh should be avoided at all costs, except at the base of large enclosures for security. Chicken wire should never be used, as it will cut up a raptor when it tries to escape, and can mangle feathers in minutes. Two layers of mesh together can act as a death trap, where the raptor can catch a leg between the layers.
Framing is best on the outside of the enclosure, so that the bird can't get anything (feathers, legs) stuck between the frame and the walls. Material that is used for walls needs to either look substantial and solid, so the bird does not try to fly through, or be soft so the bird can't hurt itself. (Wire mesh does not appear 'solid' to a raptor that is trying to escape.) Wooden slats or bars are the best, along with solid walls. These are always made vertical (up and down) so that the raptor does not have anything to climb on. This is the other reason for putting the frame on the outside- so the birds can't hang on the horizontal parts of the frame. If they climb the walls of an enclosure, raptors can break or wear their feathers, and bruise wings and feet.
The alternative to solid walls or slats is a material that is soft or will 'give' when the bird runs into it. Examples are netting, shadecloth and hessian. These generally stop the bird damaging itself, but can result in cere damage when birds panic, and frayed, worn feathers if they hang on it often. Feather damage usually takes months with netting, but may be faster with shadecloth. Most birds quickly learn not to fly face first into netting, thus avoiding cere or brow damage. Many raptors make a game of 'trampoline-ing' off the sides of the enclosure using their feet. Netting is a good material to use on large enclosures as it is light, strong and relatively cheap. However, loose netting can get tangled around a bird's foot if it hangs and turns the foot while still holding on. Netting is also easily damaged by tree branches, rats and mice, and predators, so maintenance is important. Hessian does not last long, but is good for smaller enclosures, as long as there are no frayed edges that the bird can get tangled in. Shadecloth has been used inside a wire frame, and seems to work well as long as the raptors are not inclined to hang from it. It will tend to fray, especially if being hung on by eagles, so may not be safe for larger raptors.
A standard hot box for medium to large birds can be used for raptors that need heat. This box should have a plastic or glass front, rather than wire mesh, which will damage the bird. Humidicribs and the incubators used to grow bacterial cultures in labs can also be modified and used. Any clear portions of the box need to be covered with a towel to make the raptor feel secure.
The most commonly used hospital cages for raptors are plastic airline kennels (pet packs) made for dogs. They store relatively easily and are very cleanable. An electric blanket under or draped over the outside can be used for heat. Blocks of rough wood can be used in boxes for perching.
If small holes are drilled in either side of the bottom half of the pet pack, a 1 x 2 inch or similar piece of wood can be temporarily bolted into place. These perches should either be well textured or be covered with astroturf. Towels or blankets should cover the holes at the sides of the box and the door if needed.
Birds will quickly break their feathers if they are allowed to lunge at a wire door or the holes on the side of the box. To make a pet pack really feather friendly, flip it upside-down, and use the existing air holes to bolt in the perch. Use a piece of outdoor carpet (flat synthetic 'felt' like stuff) to cover the inside of the door, attaching it with electrical zip ties.
In raptor circles, smaller holding aviaries are called mews. These enclosures are used after the bird comes out of the hospital situation. You can convert the room of a house into a mew, but birds should be acclimatised to the outdoors before they go into a large flight pen. (I consider any cage bigger than the hospital box, and smaller than 3 cubic meters a mew, although technically any raptor housing can be called mews.)
The purpose of the mew in rehabilitation is to give the raptor more freedom of movement than the hospital box, but still allow the carer to catch the bird up easily for medication or checkups. You can put a bird straight out into a giant flight pen, but if the bird is not ready for the move, you will cause it a lot of stress catching it again. The mew also lets birds that are still healing move around without giving them enough space to hurt themselves. Raptors often reach a point in their recovery where they will not sit still in a pet pack, and they will damage themselves if left there. This is when they go into a mew.
There are many different materials that can be used to build mews. Solid weather proof plywood is good for privacy and insulation, but corrugated steel works. Corrugated plastic or fiberglass should be avoided as a structural part of enclosures, because it can deteriorate in the sun and shatter suddenly if a bird hits it. All walk-in mews need to have double doors, or alternatively, shadecloth hanging just inside of the door to prevent 'premature releases'. The open part of the mew is best made from vertical wood slats or 'bars' of electrical conduit. This means the bird can see out, but can also see that it can't fly through. Another option is to use shadecloth. For an eagle mew, this would need to be heavy duty. Shadecloth is reinforced on the outside by wire mesh, and is hung inwards a bit from the wire so that a bird that flies into it bounces off the cloth, and doesn't hit hard wire on the other side. Wire mesh on it's own is just not good enough for rehabilitation facilities, and it has resulted in the death of raptors due to injury. I don't recommend netting for smaller mews, as it tends to be drum tight over these short spans, and can do damage to a raptor's cere more easily in this situation.
If you wish to rehabilitate raptors through to release, then large flight pens will probably be your greatest single expense. There are minimum suggested standards published by the IWRC that can be used as a guide to the size needed for different birds. AS LARGE AS POSSIBLE is the most important rule. A good size for all the large species and the fast falcons is 30 x 8 x 8 meters (100 x 20 x 20 feet). These large flights can also be built adjacent to each other and connect up by opening large doors. For example, two 30m flights that join at their ends and form an 'L'. A door that separates them can be opened to form a single 'L' shaped 60m flight. Another design uses flights that run side by side. A door between them at either end makes them into one 'circular' flight. The adjacent walls and doors must be designed so that a raptor on one side can't grab a raptor on the other side. There are several good web sites that show flight pens. Try searching for 'bird of prey rehabilitation' for these sites.
If you are not capable of providing a huge flight pen, a smaller one can still be useful. Build the largest pen you can. An 8 x 8 x 4 meter (20 x 20 x 10 foot) pen is good enough for Kestrels or Boobooks. A small flight can also be used as an intermediate step, until a larger one has space. Because it is unsafe to house all the different species together or overcrowd them, more than one flight pen will be needed. It is most productive to cooperate with other raptor carers and share birds according to who has space available for the species.
Flight pens can be made of the same materials described for mews. The most popular and cost effective material in W.A. is orchard or trawler netting and telegraph poles. The bottom 2 meters of the tall enclosures can be made of bird wire or 'chain link' (cyclone) fencing (normal size chain link will not hold the smallest raptors). This is buried into the ground, to keep predators out. The reason wire can be used here is that any bird put into a big flight should be able to fly up. The bird's natural inclination when trying to escape is to go upwards, so they should never come in contact with the wire. It is a good idea to wrap the top edge of the wire so that it won't hurt a raptor if the bird falls on it for some reason. Ideally, though, the netting should go all the way to the ground and have the wire on the outside. It is wise to choose a netting with as large a spacing between 'threads' as possible. This is because some birds have a habit of hanging from the top and twirling. This can result in the bird's foot getting caught, and is a life threatening situation if the bird is not untangled or cut loose. This happens more often with older netting that sags as it stretches. If you have netting enclosures, you should be prepared with a ladder and netting cutter in case of emergencies.