Review
An assessment of the published results of animal relocations

https://doi.org/10.1016/S0006-3207(00)00048-3Get rights and content

Abstract

We reviewed 180 case studies and a number of theoretical papers on animal relocations published in 12 major international scientific journals over the last 20 years. The study focused on re-introductions, supplementations and translocations (sensu IUCN, 1996. IUCN/SSC Guidelines for Re-introductions. 41st Meeting of the IUCN Council, Gland, Switzerland, May 1995. Http://iucn.org/themes/ssc/pubs/policy/hinte.htm.). We did not assess introductions. Re-introductions were the most common type of relocation (116/180); three quarters of these were conducted for conservation purposes. Supplementations (48/180) and translocations (36/180) occurred less frequently, and both were commonly carried out for reasons other than conservation. Simple descriptive statistics were used to analyse factors influencing relocation success. Translocations that aimed to solve human–animal conflicts generally failed. Re-introduction success was not found to have changed over the last two decades, but re-introductions appeared to be more successful when the source population was wild, a large number of animals was released (n>100), and the cause of original decline was removed. More complex trends were found for the effect of predation and the use of supportive measures such as provision of food or shelter, or predator control prior to release. The success of 47% of re-introductions was uncertain at the time case studies were published in journals. This was partly due to the lack of generally accepted and widely applied criteria to assess success. Very few case studies (3%) reported the cost of the relocation attempt. We conclude that there were three primary aims for animal relocations. These were to solve human–animal conflicts, to restock game populations, and conservation. Our extensive review of the present literature leads us to conclude that the value of animal relocations as a conservation tool could be enhanced through (1) more rigorous testing for the appropriateness of the approach in a given case, (2) the establishment of widely used and generally accepted criteria for judging the success or failure of relocations, (3) better monitoring after a relocation, (4) better financial accountability, and (5) greater effort to publish the results of relocations, even ones that are unsuccessful.

Introduction

Relocating animals within their range, or to parts of their former range, has become a popular tool in wildlife management, both for conservation and other purposes (16, 21, 48, 56). However, several previous studies suggest that many relocations are not successful (16, 21, 13, 44, 56), and can be very expensive (e.g. 22, 25, 40). This has led to an increased interest in what factors influence the success of relocations.

Investigations by Griffith et al. (1989) and Wolf et al. (1996) used mailing surveys to wildlife managers in selected countries in an attempt to identify some of the ecological factors influencing the success of bird and mammal relocations. Reading et al. (1997) employed a similar approach to evaluate the importance of anthropogenic factors. Although these reviews provide excellent summaries of some of the important issues, they are based on data not generally accessible to wildlife managers — people who are typically reliant on published material. Moreover, most previous reviews have (1) been limited geographically and addressed only ecological or anthropogenic issues (16, 56, 41), (2) have lacked a systematic empirical approach (21, 48), and/or, (3) have dealt with certain taxonomic groups (13, 48, 44).

We employed an approach different from earlier reviews where mailing surveys were used, and we assessed a large number of case studies as well as theoretical papers on animal relocations that have been published in major journals throughout the world over the last 20 years. Thus, our overarching objective was to explore the outcomes of relocations through a detailed literature review and summarise important unifying key themes. We acknowledge that by using published material, our sample of case studies may be several years older than assessments from mailing surveys. Also, our sample may only be a subset of all relocations because the results from a large number of relocations are never published. However, we took this approach because there are abundant published case studies on animal relocations. Therefore, an analysis and summary of the large existing body of published work may be a useful starting point for conservation biologists and wildlife managers, especially those relatively unfamiliar with the topic.

The scope of this study was considerably wider than in previous reviews — we reviewed publications dealing with all kinds of animal species in all countries of the world. In addition, because information available from published case studies often lacks detail, the questions addressed in this paper were considerably broader than those asked in previous mailing surveys.The key aims of this paper were to identify (1) where relocations have taken place, (2) what the purposes of relocations are, (3) what types of animals are commonly relocated, (4) what factors influence the success of relocations, and (5) what issues need to be addressed to make animal relocations a more efficient conservation tool in future. We are acutely aware that both mailing surveys and reviews of published literature are likely to be biased toward successful relocations (Reading et al., 1997). As the methods in this study were different from those employed in earlier assessments of animal relocations, an important additional objective was to compare and contrast the results of the two approaches and search for unifying themes common to both. Animal relocations were the focus of our review. While we acknowledge the potential importance of relocations of plants as a conservation tool (Maunder, 1994), it was beyond the scope of this study to examine them.

Section snippets

Definition of terms

In this paper, we define relocations as any intentional movement by humans of an animal or a population of animals from one location to another. In doing this, we attempt to create a neutral overarching term, and thus hope to avoid the confusion which other terms may cause [“translocation” for example has been used as both the overarching term (e.g. Griffith et al., 1989) and for a particular type of relocation, i.e. the “capture and transfer of free-ranging animals from one part of their

General trends

The database comprised 180 studies from 124 journal articles (including the review article by Short et al., 1992; Table 1). Most case studies (116/180) dealt with re-introductions, and fewer with translocations (36/180) or supplementations (48/180). (Note that the potential overlap between translocations and supplementations made it possible for case studies to fall into more than one category; hence the different categories do not sum to the total number of case studies.) Birds (79/180) and

Discussion

Our analysis of case studies showed there were three primary aims of animal relocations. These were (1) to solve human–animal conflicts, (2) to supplement game populations, and (3) conservation. This distinction has rarely been made explicitly, but is useful because the problems encountered during a relocation are likely to be fundamentally different for these three categories. We will briefly discuss the first two categories, but then focus mostly on relocations for conservation. These are our

Conclusion

Relocations are a commonly used, popular, and potentially powerful tool for the conservation of biodiversity. However, they are often carried out in an ad hoc fashion, and are not carefully monitored. In addition, most relocations are poorly documented in the published literature. Given the high publicity many relocation programmes attract, this approach has much to gain by following some simple steps to ensure that scarce conservation dollars are used in an ecologically and financially

Acknowledgements

We are grateful to M. Boyd for her assistance with collecting relevant papers. We would also like to thank Dr. K. L. Viggers and two anonymous referees for their constructive criticism of earlier versions of this manuscript.

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