Flight Enclosures

Introduction

Raptors require large enclosures in which to exercise prior to release. The use of wire, such as chain link, vinyl-coated chain link, or similar material is unsuitable for raptors such as eagles, hawks, falcons, and accipiters. A more substantial visual barrier must be provided to avoid damage to cere, feet, and feathers.

Large enclosures omit 90 percent of bird handling and therefore reduce stress and/or taming, while allowing birds to practice survival skills.

Flight enclosure dimensions for various species of raptors are listed below. They vary from the new NWRA/IWRC requirements for certain species, such as falcons, buteos, and some owls.

Methods and Materials

Posts, crossbeams, supportive construction, and the actual enclosure of the flight cages are made of cedar or treated wood. The main posts are embedded in concrete to a depth of four feet to protect the structure from high winds of up to 120 miles per hour, as often occur in Boulder County, Colorado. Cross beams are made strong enough to support heavy snow loads. The actual enclosures consist mainly of cedar wood slats (1″ x 2″). Welded wire mesh is attached to the outside of the cages for protection from predators, such as raccoons.

Protection from the Elements

Shelter from wind, sun, rain, and snow is provided with solid wooden panels on the north and west sides of enclosures, as well as on northwestern ends of cage roofs. All other sides of a cage are enclosed with wooden slats only. The birds have a choice of seeking shelter, enjoying a cool summer rain, or perching in the sun after bathing to preen. This natural material provides privacy and security, yet allows the sun to enter freely.

During the summer months, temperatures inside the cages are often ten degrees cooler than outside. Since they provide shelter from northwesterly winter winds, cage interiors are often warmer during frigid temperatures. Wood appears to be the perfect medium. Each compound is carefully spaced from the next, leaving room on southern exposures to allow plenty of sunshine to enter during cold winter months.

Specific Enclosure Information

One of the most amazing things about the enclosures is their size. There are very few such facilities in the world.

Birds of Prey Foundation Enclosure Dimensions

Standard Minimum Housing for Raptors

The Loafing Shed

Seven cages were built from an existing horse (loafing) shed and provide useful space for intermediate housing of birds that need additional shelter during the cold winter months, daily treatment, or close observation. Three sides of each cage are solid wood, with a south facing side enclosed with wooden slats to let the winter sun in.

These cages are suitable for housing excitable accipiters who are often unable to tolerate open slatted cages.

Three cages measure 20 x 15 feet; the remaining four measure 10 x 15 feet. All are 12 feet high. Birds whose injuries allow them to be outside are moved into this area first from the intensive care unit. Contact with humans is avoided which reduces stress.

The Eagle Flight

The eagle flight cage measures 108 x 25 feet and is 18 feet high. This is the minimum requirement for eagles to recover from a fractured wing, without the use of creance. Chicken wire on the outside lower two feet of the cage keeps rabbits (only dark colored animals are used for this purpose) inside for pre-release hunting experience.

Cherokee Flight

The Cherokee Flight houses primarily foster parents and educational birds. It consists of six cages, two measuring 16 x 24 feet, four measuring 12 x 24, and one cage measures 45 x 20 feet. All cages in this compound are 12 feet high.
Also attached to Cherokee is a roofed enclosure containing four outdoor hospital cages. These are occupied by birds who have no open wounds or pinned bones, and are capable of eating on their own, but still need their movements confined. Hospital cage designs were derived from Katherine McKeever’s Owl Foundation* hospital cages.

Tresemer’s Treasures

The Tresemer compound consists of six enclosures that house the smaller owls such as Long-eared (Asio otus), and Short-eared (Asio flammeus), Screech (Otus asio), and Saw-whet owls (Aegolius acadicus). The design for this and the Burrowing owl compound is taken from Katherine McKeever’s efficient designs*.One third of this compound, 12 x 24 feet, is reserved for American Kestrels (Falco sparverius), and Merlins (Falco columbarius). Since these species cannot tolerate wire enclosures, this cage is enclosed with wooden slats, which provide a greater visual barrier. The Ima and Tresemer are the only compounds which incorporate some wire, as some owls can tolerate it.

Coming In On a Wing and a Prayer

Wing and a Prayer is divided by an observation hall constructed of solid plywood, and equipped with doorways for entering the individual cages on each side. This double-door entry system prevents accidental releasals, and is incorporated into each cage compound at the BOP facility. Narrow viewing slits are cut into the walls of the hall or closet-like sheds so that birds can be observed for an indefinite time without disturbance.

The Wing and a Prayer compound measures 132 feet in length and consists of three to four cages. One is used for buteos and measures 108 feet on the outside perimeter. Another enclosure houses large owls such as Great Horned Owls (Bubo virginianus) and measures 24 x 48 feet. The third cage is used for falcons such as Peregrine Falcons (Falco peregrinus) and Prairie Falcons (Falco mexicanus). This cage may be split into two cages, each measuring 24 x 48 feet. The upper half of the wall partitioning the cages is equipped, on each end, with a large sliding door. When these doors are opened, the birds can fly in a circle of 130 feet. Perches and shelves are arranged to encourage birds to fly in a circular pattern.

The Ima Compound

The Ima compound is reserved for Burrowing Owls (Tytospeo cunicularia) and measures 36 x 24 feet. It is furnished with eleven burrows, perching posts, shrubs and small trees. One burrow is equipped for underground viewing with a glass wall and a camouflaged shelter where humans may observe and photograph the owls inside their burrow without disturbing them. Since burrowing owls normally migrate south in autumn, all the burrows are heated with thermostatic units during winter months.

The viewing burrow was constructed by building a small hill inside the cage against framework to hold the glass into place, then excavating the burrow along the glass wall.

Vegetation

Vegetation, such as grasses, shrubs and trees, appear to thrive inside the cages and give the birds natural surroundings, while providing hiding places for ground-dwelling species. During the time when young birds are trained on live prey, the vegetation simulates conditions they may find in the wild.

Water and Pools

Large concrete pools provide the opportunity to bathe and drink. These pools are cleaned every other day. The shape and size of the pools is determined by the species housed in each particular cage. A water container should never be made of slippery material, and never deeper than the bird’s belly.

Most pools at the Birds of Prey Foundation are constructed out of concrete poured over a mold made from chicken wire stretched within a depression dug into the ground. Cleaning is accomplished by sweeping out the old water with a soft broom, rinsing, and sweeping again before refilling.

Ladders and Perches

Natural perches, such as large tree branches which are kept in the natural shape, make excellent roosting places. Astro-turf (daisy door-mat material) should cover all other perches, shelves, and stair cases to prevent bumble-foot. Ladders or staircases provide birds with the opportunity to climb, if not able to fly, to high places where they feel safe and comfortable.

The size and length of the cage is properly used when there are no obstacles (perches, etc.) in the middle of the flyway. Only then will a bird attempt to fly the full length of the cage. Each enclosure is equipped with a variety of perches, shelves and hiding places, including nest boxes for shy cavity dwellers.

The birds are not forced to roost together in one crowded area. Instead they have the option to socialize if they wish or to retire to a quiet corner that allows some privacy – they are given the choice. Under the most frequently used perches, a layer of sand three to four inches deep is deposited for easy cleanup.

Cleaning

Only trained volunteers or staff (individuals usually quiet, thoughtful, observant) are permitted to clean cages; one person at a time per cage. Each cage has its own cleaning utensils, brooms, and brushes for the pools and a rake for general ground clean-up, to prevent the spread of any contagions. In the hawk and eagle cages, solid portions of the enclosures are sprayed down with a high pressure water nozzle to remove feces.

Protection from Predators

Each cage is predator-proofed with welded wire mesh or hardware cloth. This material is fastened to the outside of each cage and then wrapped in an L-shape away from the cage, to about two feet out on the ground and covered with soil. This will prevent skunks from digging under a cage to enter. All perches adjoined to any outside wall are protected with coroplast or plyboard which is attached to the wall. This should prevent racoons from pulling a diurnal bird through the cage during the night, when the bird, unable to see, won’t fly from danger. All cages should be inspected often for any damage due to predators or weather. Unused food should be disposed of well away from the cage area.

Conclusion

The advantage of large enclosures for exercising birds is quite obvious. Handling produces great stress in a wild bird, and may weaken the immune system, resulting in disease and sometimes death. Only 7% of all birds admitted to BOP die, most within hours of arrival and due to severe injuries. The Colorado Division of Wildlife recently revised laws concerning rehabilitation, including a ban on the use of creance in lieu of flight cages for exercising raptors, except in special cases for research. The BOP facility is not open to the public, ensuring a captive environment of minimum stress for the birds to recuperate in. The average release rate documented from the BOP is 63%. Since 1982, an average of slightly under 200 birds per year have been released back to the wild.

Complete manual available by contacting the Birds of Prey Foundation.

*Katherine McKeever, Care and Rehabilitation of Injured Owls, Fourth Edition (Lincoln Ontario: W.R. Rannie, The Owl Foundation)