The Effect and Value of Raptor Rehabilitation in North America

Patrick T. Redig D.V.M., Ph.D., and Gary E. Duke Ph.D.
The Raptor Center
at the University of Minnesota,
1920 Fitch Avenue, St. Paul, MN 55108

Problems Affecting Raptors
Guidelines For Rehabilitation and Management
Numbers of Raptors Rehabilitated in 1994 and Cumulative by 32 Centers in the U.S.

Since very early in its inception, the underpinnings of raptor rehabilitation and other forms of wildlife rehabilitation have consisted of medical treatment (including convalescence and preparation for return to a free-living environment), research and education. All of these elements are necessarily integrated and important to the effective conduct of a rehabilitation program. The effectiveness of any program is greatly diminished if any one of these elements is not present and maintained. The effects and value of RR can be regarded in terms of direct and indirect impacts. The direct impacts are those that derive from 1) the contribution to raptor populations by the restoration of individual birds back to the wild, 2) by medically supported research which identifies causes of morbidity and mortality as defined by birds admitted for rehabilitation, and 3) legislation and regulatory changes that are formulated on the basis of problems identified by rehabilitation. The direct effects are tangible and quantifiable within the limits of data collection abilities. The indirect effects are those that derive from 1) public and professional education about various facets of wildlife that come to light through the process of conducting wildlife rehabilitation, 2) avenues for hands-on involvement by people with wild animals, and 3) the public education efforts that accompany most rehabilitation efforts. These effects are less amenable to quantification and assessment. The purpose of this paper is to examine the direct and indirect effects in order to draw a conclusion about the role played by RR in raptor conservation.

It is typically argued in any analysis of rehabilitation that the number of birds released back to the wild is so small that it has no impact on wild populations. Allowances are made however, for endangered species of birds such as peregrine falcons (Falco peregrinus) or long-lived birds, such as bald eagles (Haliaeetus leucocephalis) and California condors (Gymnogyps californianus), where adult survivorship has a major impact on population dynamics (Grier 1980). It has also been stated that if rehabilitation were to occur on a large enough scale, the numbers of birds returned to the wild could indeed have an impact on wild populations, particularly where adult, breeding-aged birds are returned (Duke et al. 1981). Several attempts have been made to assess the scope and impact of raptor rehabilitation. No recent survey has been undertaken to determine present and past impact of raptor rehabilitation. For the purposes of this presentation we prepared a questionnaire which was sent to 65 of the approximately 250 rehabilitation facilities in the U. S. Respondents were selected on the basis of their focus on raptors, longevity, and organizational size. Questions were based in part, on a questionnaire sent to members of the National Wildlife Rehabilitator's Association in 1986 (Horton 1987).

Thirty two questionnaires were returned. Questions were designed to obtain an overall picture of the numbers of different species of raptors handled in 1994 and in the total aggregate since program inception, release rate, post-release information, recognition of special morbidity and mortality causing factors, training and educational programs affiliated with the rehabilitation operation, and impacts on policy and regulation at various levels of government organization. The data from these surveys was combined with similar data from The Raptor Center at the University of Minnesota (TRC) to generate a window by which to gain a broad overview of the present scope and nature of rehabilitation operations. The effort also identified areas in which improved record keeping and further analysis would lead to improved results in any future endeavors of this type.

RESULTS
The first question dealt with the numbers of raptors treated in 1994 and over the total time each organization had been operational. The range of operational time was 2 years to 26 years with the mean time being 11.5 years for the 32 respondents. Species of raptors about which information was sought included high profile and endangered species (bald eagle, golden eagle [Aquila chrysaetos]), peregrine falcon), common, widely distributed species (great horned owl [Bubo virginianus], red-tailed hawk [Buteo jamaicensis], American kestrel [Falco sparverius]) and species finding urban environments well-suited to their existence (coopers hawk [Accipiter cooperi]). The data is presented in table 1.

The second question dealt with the causes of injury. Respondents were asked to list and rank the top five or six causes. Over half listed vehicle collisions as the most common cause of injury. Other causes in order were miscellaneous trauma, especially windows and powerlines, followed closely by orphaned birds encountered by the public at fledging time or birds whose nests had been destroyed by storms or human activity. Shooting and toxicity were the remaining categories in the top five, except for one respondent who reported that shooting injuries accounted for 70% of their admissions. Post-Release Survival and Reassimilation of rehabilitated raptors.

Few respondents had data about post-release survival rates among rehabilitated raptors. Time, expense, and lack of other resources were the major hindrances to any large scale and conclusive studies utilizing radio telemetery. Additionally, the Bird Banding Laboratory and many state regulatory agencies have not allowed banding of rehabilitated raptors. The longest standing and largest database derived from banding is held by The Raptor Center at the University of Minnesota and we have information on about 140 returns from bands placed on about 900 birds since 1985. We previously published information on rehabilitated and released raptors from the period 1974 through 1979 (Duke et al. 1981). Examples of several cases of long-term survival of eagles and other raptors are as follows:

1. A bald eagle first banded as a nestling on 6/1/83 was admitted to TRC on 10/3/85 with a gunshot fracture of its right ulna and a near lethal case of lead poisoning (1.5 ppm in the blood). It recovered from both of these problems and was released. It was recovered again on 3/31/90, 4 years and 3 months after its previous release, this time with shotgun injuries to its left metacarpus. It was not recoverable the second time.
2. Another documented case involved an adult bald eagle photographed and identified by bandnumber in 1989 and again in 1990 in Michigan's Upper Peninsula by a wildlife photographer operating out of a blind. The band number was read from a photograph and it was learned that this particular bird had been admitted to TRC in the fall of 1981 with a rifle bullet injury that had fractured its right humerus. It was released along the Mississippi River in the winter of 1982 and was not seen again until encountered at the photographer's blind 7 years later.
3. Another documented case involved an adult bald eagle recovered near Grantsburg, Wisconsin, in the spring of 1994 with organophosphate poisoning. Released 4 weeks later at a refuge near Fargo, North Dakota, it was found a year later within 1 - 2 miles of the site of the original poisoning in Wisconsin, poisoned again, this time dead.
4. An adult bald eagle was released Feb. 7, 1988, near St. Paul and was resighted Sept/ 24, 1989 at Cheyenne Bottoms Refuge near Great Bend, Kansas.
5. A great horned owl admitted in 1984 after being tangled in a fence and sustaining a fractured digit and corneal abrasion, was released the following June. It was recovered 8 years later after a fatal collision with a car.
6. The Wildlife Center of Virginia reported one rehabilitated bald eagle nesting and fledging young the year following its release and still present 3 years later (Porter, personal communication).
7. The Raptor Trust in Millington, NJ reported a red-tailed hawk, Eastern screech owl (Otus asio) and a barn owl (Tyto alba) all known to have survived 2, 3 and 4 years, respectively, following release.
8. Treehouse Wildlife Center in Brighton, IL reported a red- tailed hawk and a barred owl (Strix varia) to be still surviving five and 7.5 years, respectively, after release.
9. A center in New York reported a great horned owl, blind in one eye, still surviving after four and a half years.
10. Tufts Wildlife Clinic reports a bald eagle still surviving seven years after release.
11. An adult bald eagle had been recovered in Arkansas on January 15, 1995 (K. Yaich, personal communication) with a USFWS marker that had been attached to a former patient at TRC. This bird had been admitted as an adult in July of 1988 from St. Louis County in Minnesota with a severe, debilitating bacterial infection (Edwardsiella tarda). It was released on August 19, 1988, near the site from which it had been recovered. It most recently had become caught by the halux in a steel-jawed trap. The injury was successfully treated and the bird was released on 16 February 1995.

Further information about survival is gained from marked and monitored peregrine falcons that have been rehabilitated and released. Four peregrines belonging to the captively-propagated and hacked founder population in the Midwest have been injured and released. Two are members of active pairs and each has produced two or more clutches of offspring since release. Additionally, a female in Colorado was injured, released, and alive for three years, producing young in two of those years.

Despite the lack of large-scale follow-up on the success of released birds, there is good evidence of survivability among birds that have been radio-tagged and/or banded suggesting that post- release survivorship of a rehabilitated raptor is a reasonable expectation provided strict criteria for performance ability are observed prior to release (Redig, et al. 1988 and appendix). Whether such survivorship is on par with that of raptors which have not sustained injury or other life-threatening events hasn't been examined, however, urban environments might provide an opportunity for such comparative studies. Discussion of Direct Impacts of Rehabilitation

Critics maintain and proponents, lacking evidence to the contrary, are compelled to agree that the rehabilitation and release of the relatively small number of individuals of a species may have little or no impact on a population and some maintain that it might