The goal of rehabilitation of orphaned raptors is to provide these youngsters with the best possible chance of survival. An important part of successful wildlife rehabilitation is to prevent the chicks from imprinting on humans, which is an irreversible process.
Imprinting is an important, natural part of a young animal’s development where it learns to recognize its own species. Imprinting utilizes the senses of sight, touch, and sound. Imprinting via sound probably begins in the egg during the pip-to-hatch stage when the parent and chick vocalize back and forth. After hatching, sight becomes an important factor in imprinting as the chick’s visual ability improves. The chick associates the images it sees with the sounds and tactile sensations with which it is already familiar.
It is not enough to prevent imprinting on humans. Instead steps must be taken to ensure the chick actively imprints on its own species during this crucial period. A young bird deprived of the sight, sound, and touch of conspecifics during this developmental stage will be unable to interact with its own kind in a normal manner.
What can be done to encourage normal imprinting? Return the chick to the parent birds whenever possible. At the time of admission, question the presenters carefully about the precise location, date, and time the bird was found as well as the location of the nest. If the chick requires supportive care it may be potentially returned to the nest after a few days of captivity.
If the nest cannot be found or the parents have been killed, then the second best way to prevent imprinting to humans is to place orphans with surrogates of the same species. Local wildlife officers, bird watchers, and naturalists can be extremely helpful in locating a nest with foster parents. Chicks already present in the nest must be approximately the same age as the orphan. Band the chicks for future identification. It is extremely important to apply the correct size band that will not constrict the leg as the bird grows. In the United States, the Fish and Wildlife Service regulates banding of migratory wild birds.
The ideal rehabilitation facility should also have non-releasable adult birds available for fostering. During the breeding season, these individuals are allowed to build nests and lay infertile eggs. Surrogate birds must be carefully selected and their health must be routinely screened. If the rehabilitation center does not have a bird of the required species available, then every attempt should be made to locate a facility with an appropriate adult.
Vultures are extremely difficult to hand-raise without the imprinting on humans. These birds are highly intelligent and they have a comparatively long nestling phase. It also takes them longer to become fully independent. Some rehabilitators employ hand puppets to forcep feed; others wear sheets to camouflage themselves; however the strong sense of smell present in these scavengers may render these tactics useless. Encourage vulture chicks to self-feed as soon as possible and place them with a suitable surrogate.
If adult foster parents are not available, a single chick intended for release must never be raised alone. Instead raise single chicks with conspecifics or at least within view of conspecifics.
Stage 1: Hatchling to nestling
Hatchlings and nestlings possess no contour feathers, only down feathers (Fig 1). Offer nestlings muscle meat and organs—no intestines, no tail. Add pieces of bone crushed with a mortar and pestle. Crush bone finely during the first few days of life). Do not include the skull or teeth. All prey items should be skinned, and then cut into tiny pieces with sharp scissors. (Supplement food with vitamins (i.e. Vionate® vitamin mineral powder, Rich Health) and a calcium supplement. Feeding unsupplemented meat for even a short number of days may induce metabolic bone disease in raptor chicks. Calcium carbonate is a much more effective calcium supplement than bone meal, which also includes substantial amounts of phosphorus. Never feed frozen or partially thawed food.
Feed hatchlings frequently, up to every 2 hours. Gradually reduce some of the feedings during the middle of the day until nestlings are fed three to four times daily. Owlets seem to do perfectly fine with a daytime feeding schedule, and I am not aware of any rehabilitators who do nocturnal feedings for owl chicks.
Most chicks will refuse food once full, but monitor the size of the crop in hawks. Owls lack a true crop. Also check the crop beforehand to be sure that it has emptied and to avoid overfeeding. The crop should empty within 2-3 hours. Weigh nestlings at least every other day. Weight gain will be slow but steady initially, but after the first few days weight gain will quite rapid. In fact, the chick should double in weight within the first 5-7 days of life.
House nestlings in small, ventilated containers or crates. Do not use a wire cage, as this will damage feathers. The cage should be tall enough for the bird to stand fully erect and wide enough to allow the chick to fully extend its wings without damaging the plumage. Place a towel on the floor for traction. A towel can also be rolled and fashioned into a doughnut shape to simulate a nest.
Provide a quiet environment away from facility noise and activity since this developmental stage is particularly prone to imprinting . Provide natural levels of lighting and a normal photoperiod. Nestlings also require supplemental heat. Provide a target temperature of 28-30ºC (82-86ºF ) for nestlings; maintain newly hatched chicks between 29-32ºC (85-90ºF) and at 40% relative humidity.
Stage 2: Pre-fledge
Hatchlings and nestlings possess no contour feathers, only down feathers. Offer nestlings muscle meat and organs—no intestines, no tail. Add pieces of bone crushed with a mortar and pestle. Crush bone finely during the first few days of life). Do not include the skull or teeth. All prey items should be skinned, and then cut into tiny pieces with sharp scissors. (Supplement food with vitamins (i.e. Vionate® vitamin mineral powder, Rich Health) and a calcium supplement . Feeding unsupplemented meat for even a short number of days may induce metabolic bone disease in raptor chicks. Calcium carbonate is a much more effective calcium supplement than bone meal, which also includes substantial amounts of phosphorus. Never feed frozen or partially thawed food.
House birds in an airliner crate or a similar cage that can be easily transported, and provide a perch such as a sturdy log.
Stage 3: Pre-fledge II
When the pin feathers begin to unfurl but down feathers are still present (Fig 2), feed the chick once or twice daily. Begin to offer whole prey sliced open with the fur intact. The bird will now regurgitate a cast or pellet of the indigestible components such as bone, fur, or feathers.
Weigh and reevaluate chicks every 4 days. The weight of some chicks may be near that of the average adult by this stage. Continue to house the chick in a crate, but move the cage to an outdoor aviary or flight cage .
Stage 4: Fledgling I
Fledgling chicks only have a small amount of down feathers remaining. At this stage, feed the whole prey sliced open once daily. Gradually leave the prey item less open until the bird is feeding like an adult. Feed nocturnal birds in the evening, and feed diurnal birds in the morning. Weigh chicks twice weekly .
Begin leaving the crate door open. The enclosure in which the cage sits should allow exposure to sunlight and rain but should also provide shelter from the elements. Also provide hiding places such as nest boxes and partitions. Shrubs or trees inside the enclosure will also provide additional hiding and roosting areas.
Stage 5: Fledgling II (Juvenile)
When no down feathers remain and full juvenile plumage is present, move the bird to a flight pen or large aviary—ideally with adult birds. The enclosure must be large enough to allow sufficient exercise. Provide perches that “give” upon landing to better mimic natural conditions. Feed juvenile birds once daily as in adults. Weigh birds once weekly.
Preparation for release: “Prey School”
Prey school is initiated after the juvenile has demonstrated consistently strong flight. Flight ability is judged by daily exercise trials which endurance, altitude, perching, as well as species-specific criteria such as silent flight in owls.
Normal, adult raptors only catch prey during one out of seven attempts, and up to 75% of first year raptors do not survive their first winter. Therefore it is crucial for juveniles to learn to hunt and/or scavenge food before release. Birds should attend “prey school” for a minimum of 6-8 days. Release a limited number of small, live, natural-colored prey such as quail, hamsters, or mice into the enclosure. To help monitor a juvenile’s progress, place prey in a large open container with some dry leaves for camouflage and high walls to prevent escape. As birds hone their skills, release more prey at a time. Medium-sized, natural-colored rabbits may also be offered to larger birds like great horned owls (Bubo virginianus), red-tailed hawks (Buteo jamaicensis), and Golden eagles (Aquila chrysaetos). Owls tend to be relatively slow learners when compared to hawks, and great horned owls remain with parent birds until late fall.
Before final release, check the plumage for broken flight feathers. Every attempt should be made to release the raptor as close to where it was found as possible. Release birds in good weather. Release diurnal raptors in the morning and release nocturnal raptors during the late afternoon or early evening hours.
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Dzialak MR, Lacki MJ, Carter KM, et al. An assessment of raptor hacking during a reintroduction. Wildlife Society Bulletin 34(2):542-547, 2006. Available at www.jstor.org. Accessed April 23, 2010.
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Ueblacker SN. Imprinting, nutrition, and rearing of orphaned raptors. National Wildlife Rehabilitator’s Association Annual Symposium. Houston, TX 1996. Available at wildlife.state.co.us. Accessed April 7, 2010.