It is becoming increasingly common for conservationists to move individual animals or entire species from one site to another. This may be either to establish a new population where a population of conspecifics (animals or plants belonging to the same species) has become extinct or to add individuals to an existing population. The former is termed reintroduction and the latter reinforcement. In both cases, wild individuals are captured in one location and translocated directly to another.
Direct translocation has been used in a wide range of plants and animals and was carried out to maintain populations as a source of food long before conservation was a familiar term. The number of translocations carried out under the banner of conservation has increased rapidly, and this has led to criticism of the technique because of the lack of evaluation of its efficacy and because of its potential disadvantages. The nature of translocation ranges from highly organized and researched national or international programs to ad hoc releases of rescued animals by well-intentioned animal lovers. In a fragmented landscape where many populations and habitats are isolated from others, translocations can play an effective role in conservation strategies; they can increase the number of existing populations or increase the size, genetic diversity, and demographic balance of a small population, consequently increasing its chances of survival.
Translocation clearly has a role in the recovery of species that have substantially declined and is the most likely method by which many sedentary species can recover all or part of their former range. However, against this is the potential for reinforcement translocations to spread disease from one population to another or to introduce deleterious or maladaptive genes to a population. Additionally, translocation of predators or competitors may have negative impacts on other species, resulting in an overall loss of diversity. Last but not least of these considerations is the effort and resources required in this type of action, which need to be justified by evidence of the likely benefits.
Despite the large number of translocations that have taken place, there is surprisingly little evidence of the efficacy of such actions. This is partly because many translocations have not been strictly for conservation; neither have they been official nor legal, let alone scientific in their approach. Successful translocations inevitably get recorded and gain attention, whereas failures may never be recorded at all. This makes appraisal of the method very difficult. One key problem is a definition of success. Is translocation successful if the individuals survive the first week or a year, or do they need to reproduce for one or several generations？Whatever the answer, it is clear that a general framework is required to ensure that any translocation is justified, has a realistic chance of success, and will be properly monitored and evaluated for the benefit of future efforts.
An example of apparent translocation success involves the threatened Seychelles warbler. This species was once confined to Cousin Island, one of the Seychelles islands, and reduced to 26 individuals. Careful habitat management increased this number to over 300 birds, but the single population remained vulnerable to local catastrophic events. The decision was taken to translocate individuals to two nearby islands to reduce this risk. The translocations took place in 1988 and 1990, and both have resulted in healthy breeding populations. A successful translocation exercise also appears to have been achieved with red howler monkeys in French Guiana. A howler population was translocated from a site due to be flooded for hydroelectric power generation. The release site was an area where local hunting had reduced the density of the resident howler population. Released troops of monkeys were kept under visual observation and followed by radio tracking of 16 females. Although the troops appeared to undergo initial problems, causing them to split up, all the tracked females settled into normal behavioral patterns.
Unfortunately, the success stories are at least matched by accounts of failure. Reviewing translocation of amphibians and reptiles, researchers C.Kenneth Dodd and Richard A. Siegel concluded that most projects have not demonstrated success as conservation techniques and should not be advocated as though they were acceptable management and mitigation practices.
环境主义保护者把动物个体或某个物种整体从一个地方迁移到另一个地方的现象已经越来越普遍了。这样做，可以在那些同种个体（属于相同种类的动物或植物）已经灭绝的地方发育出新种群，或者是为现存种群增添新个体。前者被称为“重新引入”，后者则为“强化”。在两种情况下，一个地方的野生个体被捕捉到后，直接转移到另一个地方。 在环保被人们熟知之前，直接迁移就被用于大量植物和动物中，用来维持作为食物来源的种群数量。打着环境保护旗帜的迁移数量迅速增加，因为缺乏对这种方式有效性的评定以及它潜在的缺陷，也导致了人们对这种方式的批评。迁移发生的范围从高度组织化和研究性的国际国内项目到临时放归的那些被善良的动物爱护者所救助的动物。在那些有许多种群及栖息地都与其它物种隔绝的区域，迁移在环保方面起到了非常有效的作用：可以增加现存种群的数量，或者是增加小种群的规模、基因多样性并均衡小种群的数量，从而提高其生存概率。 迁移对恢复数量已大幅减少的物种所能起到作用非常明显，也是最有可能把许多固着物种完全恢复到以前的规模或是恢复到部分规模的方式。但是，反对它的原因是它潜在的危害：强化迁移可能会使疾病从一个种群传播到另一个种群，它也可能把有害的或适应不良的基因带入种群。此外，捕食者或竞争者的迁移可能会对其他物种造成不利影响，造成整体多样性的损失。最后但并不是最不重要的考虑是为这种行动所花费的努力和资源必须和可能获得的益处相当。 尽管有大量迁移已经发生了，但是关于此类行动有效性的证据惊人地少。部分是因为许多迁移并不是完全为了环保，这些迁移既不正式也不合法，更不要说其中的科学性。成功的迁移必然会被记录下来，也会获得关注，而失败的迁移可能永远都不会被记录。这就使得评估这种方法非常困难。其中一个关键问题是成功的定义。个体在第一周或第一年存活就意味着迁移成功了吗？或者它们需要繁育一代甚至几代才算成功？无论答案是什么，有一点非常清晰：需要一个整体框架来确保任何迁移都是付出和收益相当的，都有望成功，并且可以恰当地检测和评估未来努力的益处。 明显的迁移成功例子中有一个是受到威胁的塞舌尔刺嘴莺。这个物种曾经只存在于库金岛（塞舌尔群岛中的某一座），个体数量减少至26只。谨慎管理栖息地使得它的数量增加到了超过300只，但面对当地灾难性事件时，该种群依然脆弱。人们决定将刺嘴莺迁移到附近的两座岛屿，以降低风险。迁移发生在1988年和1990年，两次迁移都繁殖出了健康种群。成功的迁移经历似乎还在法属圭亚那地区的红吼猴身上发生过。因为水力发电厂淹没了这个地区，一个猴群从这个地方迁移出来。放归地是一个因当地狩猎而导致猴群密度降低的区域。被放归的猴群一直处于被观察之中，其中还有16只雌性被无线电追踪。尽管猴群一开始似乎存在一些问题，还导致了它们的分裂，但是所有被追踪的雌性都已经有了正常的行为模式。 不幸的是，成功故事的数量和记录在案的失败数量至少是相等的。回顾两栖动物和爬行动物的迁移，研究人员C.Kenneth Dodd和Richard A. Siegel总结发现大部分项目并没有展示出环保技术的成功，因而不应该被提倡，尽管它们好像是可接受的管理方式和缓和措施。