Reintroduction Guidelines

By Richard Hudson

Relocation, repatriation, and translocation (RRT) programs involving reptiles have become an extremely popular conservation strategy to mitigate the loss of habitat, individuals, or populations in areas that have experienced declines or extirpations (Dodd and Seigel 1991). However, few reptile RRT programs have been successful or properly monitored to determine success or failure. Some notable exceptions include the introduction of captive-reared gharials, Gavialis gangeticus, to areas where they had been reduced or eliminated (Choudhury and Choudhury, 1986); the release of over 600 headstarted Orinoco crocodiles, Crocodylus intermedius, in Venezuela (Thorbjarnarson, 1997); the restoration of Galapagos land iguanas, Conolophus subcristatus, and Galapagos tortoises, Geochelone elephantophus, to areas of former abundance (Cayot et al 1994); and the reintroduction of Anegada iguanas to part of their former range (Goodyear and Lazell 1994). Preliminary observations by Tolson (1996) indicate a successful restocking of Virgin Islands tree boas, Epicrates monensis granti, to an island rendered free of introduced predators, and J. Behler (personal communication) reports successful reintroduction of a group of 76 Gopher tortoises, Gopherus poylphemus, to St. Catherine's Island, Georgia. While representatives from most reptilian orders have been successfully repatriated with encouraging results, the outcomes of other well-publicized headstart/release efforts, [e.g. Kemp's ridley, Lepidochelys kempi, and other sea turtles (Jacobsen 1993; Bowen et al., 1994) and the Puerto Rican crested toad, Peltophryne lemur (Johnson 1994)], have proved difficult to monitor and remain questionable.

While various authors disagree as to what constitutes a successful reintroduction (Burke 1991), it is clear that the fledgling science of conservation biology, including restoration ecology and RRT, cannot stand still while these issues are rectified. Given the enormous loss of biodiversity today, wildlife managers need to be willing to consider RRT programs as viable strategies to combat the impending extinction crisis. Although by no means a panacea, RRT programs should be considered an option in any recovery effort (Burke 1991). However, the technology needs to be refined and improved if these programs are to become widely utilized. The methodology and results of both successful and unsuccessful RRT experiments need to be presented in detail to ensure that future efforts benefit from past experience (Dodd and Seigel 1991).

For West Indian iguanas, it is apparent that at least three taxa, the Jamaican iguana, the Anegada iguana, and the Grand Cayman iguana, will require assistance from captive headstart/release programs if their wild populations are to recover and survive into the future. Both taxa have been reduced to critically low numbers and, given current circumstances and rates of decline, appear headed for extinction unless immediate action is taken.

General Concerns

Conservation biology has been described as a crisis science (Soulé 1985) and as such may not always be subject to the same statistical standards as other scientific fields (Burke 1991). Likewise RRT programs, an integral part of conservation biology, are in the experimental stages. Unfortunately, for some taxa the need to undertake active recovery strategies, including RRT programs, is urgent and little time remains for experimentation. There are few tested standards on which to rely, but this alone must not thwart well-conceived RRT plans. Bold actions, though exercised with due caution, must be taken within the next several decades if several of the more highly endangered large iguanas are to be preserved. Throughout this process, establishment of feedback loops to alter decisions based on new and changing data is critical.

Dodd and Seigel (1991) have addressed a number of topics that should be considered prior to advocating or undertaking RRT projects, including known causes of decline; biological, habitat, demographic, and biophysical constraints; population genetics and social structure; and disease transmission. Reinert (1991) has expressed concern regarding genetic as well as social considerations, citing examples of aberrant behaviors in translocated snakes. Burke (1991) questions whether RRT programs are cost effective for improving species survival, and both Reinert (1991) and Dodd and Seigel (1991) stress the importance of long-term monitoring to ascertain success. Prior to any reintroduction, the original threats to the population must be understood and potentially controlled.

The potential to introduce exotic pathogens into naive natural populations through release of captive reptiles is widely recognized. This route of transmission has been implicated in an epizootic outbreak of upper respiratory tract disease (URTD) in wild desert tortoises, Gopherus agassizii, in the Mojave Desert of California (Jacobsen et al. 1991). Jacobsen (1993, 1994) stresses that while reptiles can harbor an array of pathogens, the ability to screen for those few that are known to be significant is crude at best. The importance of developing pre-release health screening protocols and methods has been emphasized by a number of workers (Beck 1992; Dodd and Seigel 1991; Jacobsen 1994; Raphael 1994). Whenever feasible, in situ rearing and headstarting facilities are preferable to reduce the chances of introduction of exotic pathogens.

One of the factors that can inhibit the success of RRT programs is the potential inability of the progeny of captive populations to withstand the rigors of natural environments (Murphy and Chiszar 1989). Chiszar et al. (1994) defined competent offspring as those possessing the behavioral, anatomical, and physiological characteristics necessary for survival in natural habitats. The ability of captive-raised animals to find food and mates, avoid predation, locate refugia, and select appropriate microhabitats once released should be investigated (Chiszar et al. 1993). At least in part, deficits in competence may account for the lower success rate of reintroductions involving captive-born rather than wild specimens (Griffith et al. 1989). Stressing that factors such as strength, endurance, and immunological function are crucial to the success or failure of RRT programs, Murphy and Chiszar (1989) strongly advocate research that rigorously assesses competence. In some cases, releasing larger numbers of animals can at least partially compensate for reduced fitness and/or competence of captive-reared specimens (B. Johnson, personal communication).

Although it is commonly assumed that natural behaviors are innate in amphibians and reptiles and therefore present in healthy specimens regardless of rearing history, no research exists verifying that effective coping skills exist in captive-raised individuals (Chiszar et al. 1993). However, it appears that certain species of reptiles can, in the absence of any pre-release training, adapt, survive, and even reproduce following release into natural habitat. A recent example is the monitored release of captive Virgin Islands tree boas onto Cayo Ratones (Tolson 1996). More than half of the released snakes survived their first year, and at least four of these were neonates. One female released as an adult was recently recaptured gravid.

Several recent conservation programs for iguanas in the Galapagos and West Indies suggest that large iguanid lizards may be genetically hard-wired for many critical natural behaviors and should be considered viable candidates for reintroduction and population supplementation.

1. The release of 710 Galapagos land iguanas into the wild over a 10-year period was initiated in 1976 following the near extirpation of populations on Isabella and Santa Cruz by wild dogs (Cayot et al. 1994). A third island, Baltra, had not supported iguanas since World War II. The majority of repatriated iguanas were captive-bred from adults collected from declining populations and reared under captive and semi-captive conditions. The Baltra breeding stock was taken from a previously relocated population experiencing poor recruitment. The success of this program has been impressive, with nearly 400 juveniles and 21 adults repatriated on Isabella since 1982. Annual monitoring indicates a growing population. In 1991-92, 59 5-year old iguanas were established on Baltra, the first to have existed there in over 40 years. The success of these programs is encouraging and is closely linked to active predator control efforts. Dogs were eradicated prior to releasing iguanas, and cats are poisoned semi-annually (Cayot et al 1994).
2. The reintroduction of a group of wild-caught Anegada Island iguanas to Guana Island in the British Virgin Islands has resulted in the successful establishment of a second population reservoir for this endangered lizard (Goodyear and Lazell 1994). Between 1984 and 1987, three males and five females, two of which were gravid, were released on Guana. One female apparently nested successfully, as subadults were subsequently seen in 1987 and are believed to represent some of the adults seen in 1991-92. A reproducing population is now established, and a 1992 census estimates that about 20 adults and several juveniles now inhabit the cay. Although still preliminary, these results bode well for re-establishing iguanas within their former range. As on the Galapagos, this project has entailed the elimination of feral cats.
3. In 1990, the National Trust for the Cayman Islands initiated an integrated conservation program for the highly endangered Grand Cayman iguana, with the long-term goal of securing wild, reproducing populations in protected areas without the need for constant human intervention. The program includes five components: field research, captive breeding, public education, habitat protection, and supplementation of the wild population. All components are now in progress, including the first releases, which have proved successful (Burton 1994b). Although no evidence was found of wild iguanas at the potential release site, the Salina Reserve, the area supports suitable habitat. The first three releases were captive-bred, sterilized hybrid males with internal radiotransmitters. The releases occurred in June and July 1993, and the lizards were tracked at regular intervals. Although one animal was killed by a dog outside the reserve, the remaining two individuals were still well established at the study site in December, 1993. These results are encouraging in that naive captive-bred iguanas demonstrated a surprising ability to adapt to life in the wild, locate food and retreats, and exhibit characteristic territorial behavior. These results indicate that captive-bred iguanas can be successfully re-established in the wild provided adequate protected habitat can be secured.

Cayman Islands National Trust iguana headstarting facility at the Queen Elizabeth II Botanic Park, Grand Cayman.

Criteria for RRT programs

According to the IUCN (1995), translocation is the deliberate and mediated movement of wild individuals to an existing population of conspecifics. Re-introduction is an attempt to establish a species in an area that was once part of its historical range, but from which it has been extirpated or become extinct. Re-enforcement/supplementation is the addition of individuals to an existing population of conspecifics. Conservation/benign introductions are attempts to establish a species outside its recorded distribution, but within an appropriate habitat and eco-geographical area. These latter introductions should be attempted only when there is no remaining area within a species' historical range and enhanced survival of the species will result. Although reintroduction is often used to describe the release of animals into presently occupied habitat, the term translocation may be more appropriate in such circumstances. Kleiman et al. (1984) emphasize that the origin of released animals (wild versus captive) may have a major impact on the potential success of translocation efforts. The Reintroduction Advisory Group of the American Zoo and Aquarium Association has prepared a comprehensive set of guidelines pertaining specifically to animals born or held in captivity (Beck 1992).

According to the Guidelines for Re-introductions provided by the IUCN/SSC Reintroduction Specialist Group (IUCN 1995), the objectives of reintroduction are to: a) enhance the long-term survival of a species, b) re-establish a keystone species (in the ecological or cultural sense) in an ecosystem, c) maintain and/or restore natural biodiversity, d) provide long-term economic benefits to local people and/or national economy, or e) promote conservation awareness. The success of any RRT effort should be measured in terms of its goals and objectives. In most cases, success is defined as a stable, self-sustaining, viable population at the reintroduction site (Kleiman et al 1984; Dodd and Seigel 1991). Burke (1991) discusses concerns regarding the point at which a population can be called self-sustaining and how stability can be objectively determined.

Currently, recovery efforts are underway for two Critically Endangered West Indian iguanas, the Jamaican iguana and the Grand Cayman iguana. For both taxa, headstarting and supplementation of the wild population are among the primary goals, and preliminary releases have already been attempted.

The Cayman Islands National Trust program for the Grand Cayman iguana has multiple objectives, one of which is to generate sufficient offspring for release into suitable habitat. Unfortunately such habitat is becoming scarce on Grand Cayman, and feral predators are an increasing problem. Establishing a stable population on protected property is critical, and the proposed Salina Reserve site is promising in this regard. A Trust-owned property, the Queen Elizabeth II Botanic Park, is protected and may provide suitable iguana habitat as evidenced by the presence of a resident male over the past three years and a successful pilot release in 1994. Park development has improved habitat suitability in recent years, and the area lacks only nesting sites and associated retreats. It is hoped that the release of females within the park will attract roaming males, which usually maintain extensive home ranges, from outlying areas, thus providing a second area from which to repopulate other sites. While it is apparent that recovery of Grand Cayman iguanas will require a multi-faceted approach, reintroduction clearly constitutes a necessary component of this program.

A group of headstarted iguanas at the Hope Zoo in Kingston, Jamaica.

A similar situation exists for the Jamaican iguana. Considered extinct for nearly half a century, the Jamaican iguana was rediscovered in 1990 and has since become the subject of intense conservation and research efforts. Existing only in the dry limestone forests of the Hellshire Hills region of southeast Jamaica, a remnant population of perhaps 100 animals survives. Two active nesting sites were discovered in 1991, and field work has focused on protecting these sites and deterring hunters and charcoal burners from core iguana areas. High juvenile mortality associated with mongoose predation is widely recognized as the single most important factor keeping this population at low levels. A 1993 Population and Habitat Viability Assessment workshop indicated that without reducing juvenile mortality through headstarting, this small population was headed for extinction within 50 years. The recovery strategy includes guarding nests and harvesting 50% of the hatchlings for headstarting at the Hope Zoo in Kingston. Headstarted iguanas will be released after 4-5 years, when presumably they will be large enough to avoid mongoose predation. Control of feral dogs and mongooses will need to be implemented concurrently to increase survival of the released iguanas.

Pre-release considerations

In preparation for the eventual release of headstarted Jamaican iguanas into the wild, a pre-release medical screening protocol was developed in 1994 to assess the health status of the captive colony at the Hope Zoo. Cloacal cultures and fecal exams were conducted to screen for abnormal internal parasites and bacterial pathogens, and blood chemistry panels were performed to establish normal values. Attempts to sample the wild population in order to correlate captive values with those of free-ranging counterparts also need to be made. Similar health screening programs should be incorporated into pre-release preparations for any iguana species destined for release to the wild (Alberts et al., 1998). This is especially important if iguanas have been in captivity for a long period of time, or have lived in colonies that have experienced any health problems or disease. An Amphibian and Reptile Veterinary Advisory Committee, established under the American Zoo and Aquarium Association, has published recommended protocols for quarantine and pre-release health screening. This group is available to assist with this process, and information can be obtained from: Bonnie Raphael, D.V.M., Animal Health Center, Bronx Zoo/Wildlife Conservation Park, 2300 Southern Boulevard, Bronx, New York, 10460 U.S.A., Tel: (718) 220-7104.

Other forms of pre-release conditioning may be necessary as well. The original release strategy for Jamaican iguanas called for a hardening facility to be built in the Hellshire Hills for acclimating headstarted iguanas to wild forage and local conditions. Due to financial and logistical constraints, this idea was temporarily abandoned in order to assess the survival rate of iguanas taken directly from the Zoo. After five years of headstarting, the first pair of iguanas was fitted with radiotransmitters and released at their hatch sites in March 1996. Experiences from 1995 had shown that radiotagged hatchlings released near the nest site tended to remain in the same vicinity, and it was hoped that older iguanas would display a similar site fidelity. Results were mixed, with both animals experiencing some initial weight loss and the male losing his transmitter. Whether this was related to weight loss is unknown; the female also lost considerable weight and was recaptured so that her transmitter attachment could be secured. She was released again, and was apparently feeding and doing well soon afterward (N. Mitchell, personal communication). Six additional iguanas released in 1997 all appear to have adapted well.

Radiotracking released iguanas in the Hellshire Hills, Jamaica.

Significant differences exist in the feeding regimes of the Grand Cayman and Jamaican iguana headstart programs that may have serious implications for the survival of released iguanas. Captive Grand Cayman iguanas are raised almost entirely on commercially available alfalfa-based livestock pellets. Because they are unfamiliar with fruits and vegetables, they may be more inclined to feed on native vegetation once released. In contrast, Jamaican iguanas are primarily fed commercially available fruits and vegetables. This diet is highly palatable to the iguanas, and they consume it readily and grow rapidly. However, its high moisture content may predispose iguanas to substantial water weight loss following release. Furthermore, ingestion of a highly palatable fruit diet as a primary food source may cause iguanas to adapt more slowly to native vegetation. Given this, acclimation of headstarted iguanas to natural foods prior to release may be advisable.

Financial considerations

Based on limited experiences with iguana headstart/release programs on both Grand Cayman and Jamaica, it is apparent that practical financial considerations must be evaluated prior to developing a release strategy. Depending on the length of the program, the headstarting process itself represents a substantial monetary commitment, although this is reduced somewhat if done within the range country. Although over $20,000 was raised in the United States to fund the new iguana management facility at the Hope Zoo, the 2-year old facility is at capacity and needs expansion. The National Trust's new iguana facility cost a total of $14,700, donated from a single outside source. In addition to the expenses of pre-release conditioning and health screening, facility construction alone can impose a considerable financial burden on local conservation efforts.

Expenses do not end once animals have been returned to the wild. In fact, the most costly aspect of headstart/release programs may be field monitoring, which is critical to all RRT programs. If radiotelemetry is utilized, and this certainly appears to be the most effective method of gauging short-term survival, then costs increase considerably. Even after the initial expenses of equipment purchase, the annual cost of the Jamaican iguana field project is estimated at a minimum of $10,000 U.S., excluding an additional full-time employee. According to Kleiman et al. (1984), the most effective and successful RRT programs have been comprehensive efforts involving a large multidisciplinary team and considerable resources. These authors discuss 13 criteria that should be considered prior to implementing a reintroduction (Table 6).

RRT technology and its application to iguana conservation is in its infancy, and there is much to be learned as this process moves forward. But is it only by moving forward that we will begin to gain the experience and insights necessary to make these strategies successful. In particular, radiotelemetry techniques must be further developed and openly shared. Conservation strategies must be developed while time remains to refine the methodology and perfect the techniques that will ultimately prove to be an essential component of recovery strategies not only for endangered iguanids, but other taxa as well.

Table 6. Translocation/Reintroduction of Grand Cayman and Jamaican Iguana: Do appropriate conditions exist? (Scale 5=best).