Aardvarks to Zebu: Post 1

Hello!  We have a new column here at IWRC.  Each month we will choose a challenging rehabilitation question and poll two to four experts on the topic.  In this, our first post, we chose the question “Would you release a one-eyed diurnal raptor?” and asked it of three long time raptor rehabilitators, Louise Shimmel, Randie Segal, and Marge Gibson.  If you have your own burning question, email me at director@theiwrc.org.  The question just might find its way into a future post!

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Aardvarks to Zebu:

Wildlife Rehabilitation Quandaries and Conundrums

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Would you release a one-eyed diurnal raptor?

Louise Shimmel – Cascade Raptor Center

No – with very few exceptions.  Turkey vultures, perhaps – though there’s increased risk of them being hit by a car on their blind side.  They are already clumsy getting off the ground, losing even a couple of seconds of awareness of the approach of a predator or car could be fatal.  However, since they are often on the ground in the company of others who could provide an early warning system, I would definitely consider releasing a one-eyed turkey vulture (we don’t get black vultures, and I know little about them).  I once thought harriers might be possible, but have had only one with an eye injury that was otherwise releasable, and she definitely ran into things.

I know of one case of an immature bald eagle in Alaska.  She did not have the personality for life in captivity, so it was decided to try releasing her down in the Skagit Valley of Washington, with telemetry.  The Seattle zoo and Washington DFW followed her for a couple of years, as I understand it, and she was eating more carrion than normal, but she did survive.  I tried it once with an adult female red-tailed hawk, on the assumption that she knew how to hunt, she probably had a mate to help feed her part of the year, she’s also a carrion eater.  She apparently did fine through the summer, either from a mate providing food and/or abundant prey or carrion – but she came back in starving, once the weather turned in October.  My main concern is the loss in the field of vision, especially for the falcons who hunt at speed and need particularly good depth perception.  Even more critical would be eyesight for the accipiters, who are not only hunting at speed but maneuvering through cover at the same time.  So, my basic response is no – a one-eyed diurnal raptor is not releasable.

-Louise

Randie Segal – Wind River Wildlife Rehabilitation Center

First, it would depend on the age of the bird. If it is a young bird (hatch year), then I would be very hesitant. I would be concerned that the bird is too naive to be successful without his depth perception . I would evaluate the bird with the same methods as an older bird. An older bird with more experience, I would be more likely to consider release. The experience of the bird could be enough to compensate for the loss of depth perception.I would suggest flying the bird with a Falconer or watching carefully in a large flight to see if the bird is hitting his perches with regularity. We also would want to know how alert the bird is in his surroundings.This way you could evaluate the effects of the depth perception loss. If you add live prey and the bird kills repeatedly, the bird would be released to enjoy life in the sky.

-Randie

Marge Gibson- Raptor Education Group Inc

In most cases, I would not.  However, as in other aspects of wildlife rehabilitation, it is hard to use a “cookie cutter” approach to this question.   It is good to think the question through for each patient. That way you will understand the issue thoroughly and feel satisfied in your decision on your patient’s behalf.

Your decision to release a one-eyed raptor depends on many things, including the age of the raptor, species, the type of injury or disease that caused the blindness, and even the habitat and climate zone in which  the raptor lives.  Ultimately the bird’s ability to hunt and demonstrate depth perception accurately in a large flight, will give you your answer.   We have admitted raptors owls, buteos and eagles that have old injuries to their eyes.  If they were in good weight when admitted and doing well in the wild, we may consider releasing them again. Admittedly, one-eyed patients released to the wild at R.E.G.I. are a low percentage.

It is important to begin with a basic premise, that your patient with one eyed blindness will have a shorter expectancy if released to the wild than a raptor with prefect vision.   If your patient has adjusted well to captivity and will be placed in a terrific education facility, consider that option first for your patient.  If the bird is not comfortable in captivity, the following list may help with your decision:

1. Was the injury to the eye only or was head trauma part of the initial injury?  One-eyed blindness may be only part of a larger diagnosis when head injury in the cause. Head injuries complicate existing blindness.  The bird is not generally a candidate for release.

2. Is the blindness caused by West Nile Virus?  Blindness caused by WNV is not always detectible by an eye exam.  WNV can compromise the area of the brain that controls vision. This condition may deteriorate over time.  The eye itself may appear quite normal.  Typically, a raptor affected by WNV blindness will run into things in a flight, not hit perches accurately or land short of a target.  A bird of this description should never be released to the wild.

3. Does the bird hold its head in a natural manner or is it tipped to one side?  Head injuries can affect not only the brain and eyes, but the auditory system as well. A bird with previous head injuries may hold its head in an unusual position. This patient should not be considered releasable both for medical reasons and for natural behavior (posture) which is important in the wild.

4. Will your patient be released in an area without severe weather conditions?   If you live in the far north and your patient is not a migratory bird, do not release it to the wild.  Eyes and the surrounding socket area loose tissue, fat padding and circulation after a traumatic injury or enuculation surgery.  The fore-mentioned problems make the area subject to pain and frostbite in severe temperatures.  If you cannot assure your patient will have temperate weather in which to hunt and utilize carrion do not release it.

5.  Young birds that have never hunted before their eye injury should not be released. The one exception is if the bird was first flown by a falconer for a year or more and proved itself to be a skilled hunter.

6. Was the patient older, had a healed eye injury and previously adjusted to hunting with its disability?  Does the patient have a mate?  An older patient that has learned to hunt successfully with its disability was in good weight and feather condition when admitted, is a candidate for release.

We have released one-eyed raptors and through banding records found, they lived many years in the wild with their disability.   Studies have shown one-eyed raptors eat more carrion than wild birds of their same species.  Our banding results indicate one-eyed birds often lose their life when hit by car or attacked by other predators.  Videos exist of both adult Bald and Golden Eagles on active nests where one parent bird has a blind eye.  It is assumed the eagles were already a mated pair when one was injured and developed one-eye blindness.   Most biologists assume a one-eyed bird would not be “selected” as a mate over a bird without a disability.

One-eyed blindness is a serious disability for a raptor.  In most cases, it is not a good option to release them back to the wild unless a special circumstance exists.

-Marge