Should we Reintroduce Locally Extinct Species to their Historical Habitat?

The Implications of Species Reintroduction Using the Case Study of the White-tailed Sea Eagle (Haliaeetus albicilla, L.) in West Scotland


According to the International Union for Conservation of Nature (IUCN): reintroduction projects “attempt to re-establish species within their historical ranges through the release of wild or captive-bred individuals following extirpation or extinction in the wild1. With the increasing human impact on the natural environment, a growing number of species worldwide are threatened with declining populations and extinction2. Therefore, reintroduction programs are becoming increasingly used in an attempt to reestablish populations of threatened species3, 4, 5.

In 2005, an IUCN Reintroduction Specialist Group (RSG) website reported 489 animal species which are part of recent, current or planned reintroduction projects for conservation purposes6. However, only 11-62% of reintroduction programs are successful6, and many animals die soon after release7. Additionally, reintroduction programs are expensive, possibly costing several thousand dollars, to up to 1 million dollars annually8, 7.

Therefore, controversies around reintroduction projects are frequent, and scientists and conservation managers have to have strong scientific, cultural and/or aesthetic justifications for a reintroduction. The following paragraphs will be exploring the different issues around animal reintroductions through the case of the white-tailed sea eagle (Haliaeetus albicilla) in West Scotland; its history, the reintroduction process and the problems encountered.


In the 18th century, H. albicilla (Click Box 1 below for Case Species Overview) was fairly common and widespread in Scotland10.  In the UK they have been recorded in ancient art and local folklore:  in Orkney the bird was treated as a totemic symbol, regarded with superstitious respect11.  During the Dark ages, the felling of woodlands and drainage of wetlands to establish farmlands led to the decline of H. albicilla habitat11. Persecution on these new farmlands started due to lack of tolerance, and so began the decline of H. albicilla in the UK11.

Due to illegal killing, H. albicilla went extinct in the UK during the early 20th century10. They were persecuted by shepherds, gamekeepers, fishery owners, skin collectors and as the birds became increasingly rare; egg collectors10.  The spread of sheep farming in the Western Highlands lead to a conflict between H. albicilla and farmers scared of losing livestock – and using poisoned baits and firearms, the farmers had a devastating advantage11.

Box 1 Sea Eagles


Following previously failed reintroduction attempts of H. albicilla, in 1975, the Nature Conservancy Council (now the Scottish Natural Heritage) began a more long-term project based on the Isle of Rum in the Inner Hebrides11.

Over the next ten years, 82 eaglets were imported from Norway (where the H. albicilla population was still expanding) to the Isle of Rum11. It takes a couple of years for H. albicilla to reach maturity and be able to breed. Therefore, it was only in 1983 when the first eggs were laid, and 1985 was the first year to see a successful breeding11.

In 1993 and 1998 an additional 58 Norwegian H. albicilla were released. By 2003 just over 30 pairs were established and 26 eaglets successfully fledged. There is now an established population of H. albicilla with 50 breeding pairs in the west coast of Scotland10. The third phase of the reintroduction is to bring the birds to East Scotland10.

All of the birds released are fitted with radio tags, allowing them to be continuously monitored through radio-tracking and public sightings10.


European Union legislation is very supportive of reintroduction projects; The Convention on the Conservation of European Wildlife and Natural Habitats (1979) was the first wildlife treaty to encourage parties to reintroduce species for conservation.

As with all other birds of prey in the UK, H. albicilla is given the highest degree of legal protection under the Schedule 1 of the Wildlife and Countryside Act 198110. Along with the Nature Conservation (Scotland) Act 2004, it is an offence to intentionally take, injure or kill an H. albicilla or to take, damage or destroy its nest, eggs or young10. It is also an offence to intentionally or recklessly disturb the birds close to their nest during the breeding season, and violation of these laws can cause a fine of up to 5,000GBP and/or a prison sentence of up to 6 months10.

SNH and RSPB staff are constantly working to identify persecutions of H. albicilla. Eagle nests are closely watched to ensure minimal disturbance during breeding10.


H. albicilla is now very much threatened throughout most of its historical range due to habitat loss, human disturbance and pesticides12. As the species has declined due to human impacts, it is widely agreed from the conservationists’ side that it should be encouraged to return12. If humans were the main cause for a species’ demise, we are then arguably responsible for its return.

Due to its slow re-colonization ability, this is a further reason for human interference13. As the West of Scotland is relatively undisturbed, it seems an appropriate area for reintroduction12. As the peregrine Falco peregrinus, H. albicilla can also act as an indicator of health of the marine environment12: valuable especially in these times of great environmental change. Lastly, eagle tourism was calculated to be worth 1.4-1.6GBP million annually on Mull13 – a strong economic reason for its reintroduction.


There are some challenging questions regarding re-introduction projects. For instance, at what point in history should we start considering animals for reintroduction? Bison, reindeer, wolf and lynx were all once found in the Peak District14. Brown bears survived in Scotland to around 1057. Should all these animals be considered for reintroduction projects? Further questions arise regarding the definitions of ‘native’ and ‘introduced’ species14, especially as EU legislation is supportive of introduced species control – can the brown hares (introduced by the Romans to the UK around 2,000BP) still be considered as a strictly introduced species to therefore be controlled? Why should we prioritize some species for reintroduction over others, and how do we make these decisions?

We also have to question whether the often high mortality rate15 during the re-introduction process is acceptable. The large resource use in these programs furthermore have to be justified; is a reintroduction program worth more than allocating the resources used for protecting nature reserves15?

Therefore, scientists and conservation managers have to ensure that their reasons for reintroduction are sound and scientifically supported. If not, conflict can arise with local people and other stakeholders. The following paragraphs will discuss further barriers and threats to reintroduction programs.


Population viability is important to consider in reintroduction programs – if the introduced population is too small, the resulting rates of inbreeding and loss of genetic diversity can reduce the long-term fitness of a population16, and lead to the inevitable failure of the program. Therefore, programs should try to create and maintain populations with high levels of genetic diversity by starting with the highest possible number of reintroduced animals and ensuring a high initial population growth rate17.

As the population of H. albicilla is still relatively small in Scotland, it is still vulnerable. It was reported that the first reintroductions done by that time (1975 and 1985) had a probability of 0.6 of becoming extinct in the next 100 years18. However, when modeling an addition of 60 juveniles, there was a significant reduction in extinction risk18. Therefore, the two additional reintroduction phases followed. The survival rate of the Scottish population of H. albicilla is now the same as that found in Norway and the birds seem to be establishing a self-sustaining population11.

This highlights the importance of long-term projects to monitor populations and their dynamics. There is the possible necessity of continued re-introductions years after the project was started, to ensure that stochastic events do not eventually lead to the extinction of the species trying to be reintroduced. This has understandable economic implications – a program will unlikely be a one-off investment.


As Tilt (1989) writes: The general public’s perception of an endangered species issue may not seem important to a wolf lover or a darter supporter. But if the general perception runs against an animal or plant’s continued survival, all the biological data in the world will be useless against the perception.”19

As animal introductions often cause a radical change to the status quo, there is great potential for controversy13. This can be related to damage claims, danger to human safety, and increase in the conservationists’ control over the natural environment, or the sense of encroachment on land rights13.

Since the 1990’s, the most controversial issue with H. albicilla introduction was their alleged predation on lambs13. This led to extensive research by the SNH on eagle diet on Mull which concluded a great variability in diet between breeding pairs13. Some eagles were found to scavenge on lamb carcasses, but these were mostly unviable animals13. While most birds do not pose a threat to livestock, some cases have arisen where individual eagles have caused a local problem10, and the SNH studies found one eagle pair actively killed lambs13.

To counteract these issues, conservation officers work closely with farmers and land-owners. SNH also offers positive management schemes to farmers with land containing eagles on Mull (The Natural Care Mill Eagle Scheme) and parts of Skye10.  There has been a notable change in local attitudes, especially with the increase of tourism due to the birds; on Mull, a small public viewing hide is operated by the islanders along with SNH, RSPB and the Forestry Commission11. Continuing efforts to liaison with the public is vital to ensure the future for the eagles in Scotland.


After the middle of the 20th Century, the danger of bioaccumulation to the eagles became clear. Organochlorine pesticides (DDT, DDE etc), polychlorinated biphenyls (PCBs) and heavy metals caused a significant decline in eagle populations11. H. albicilla sometimes predate on fulmars – a seabird thought to be the source of DDT and PCBs found in some eagle eggs10. Additionally, they fall victims to poisons illegally set for foxes and crows10.

H. albicilla continue to be deliberately killed, with their nests still targeted by egg-collectors10. As many as 40 birds can gather around a carcass, making them vulnerable to deliberate poisoning12. For such a small population, any nest or eagle losses have a direct impact on the whole population10.

Therefore, it is vital that protection and surveillance of the nest sites continues to prevent disturbance10. Local resistance to the project has to be mitigated as previously described. Research on the long-term effects of currently used pesticides and other chemicals is needed. Without knowing the effects of modern-day agriculture and industry on the birds, we will not be able to adapt conservation methods to maximise the success of the reintroduction program. It will further aid effective decision making and resource allocation.

This highlights the more general need of investment in monitoring of the reintroduced population, research into its interaction with humans as well as the current possible effects humans may still have on the populations.


The issues regarding species reintroduction are complicated, and this essay has only been able to highlight some of the main ones. With the H. albicilla, while the reintroduction project seems successful, issues such as further habitat loss, competition with golden eagles and loss of food sources (with a decreasing ocean fish stock) have to be further considered. It is clear that reintroduction projects have to be carefully planned, with complex ethical issues needing to be considered along with the requirement for socially acceptable arguments if a reintroduction project is to succeed. Conflicts can arise with local communities in the area, highlighting the need for effective stakeholder involvement and educational programs to minimise conflict. Investment in reintroduction programs is high: they are time-consuming and expensive, with active management necessary for years after the initial animal is released. However, in a world severely affected by increasing human populations and large scale environmental changes, reintroduction programs are possibly the last chance of survival for many species. If we want the iconic orang-utans, Bengal tiger or Sumatran rhinoceros to continue to survive in the wild, it is likely that these species’ only hope is to successfully design and implement extensive and expensive reintroduction programs. Lastly, research efforts should consider not only the current effect of humans (e.g. agricultural biocides) on reintroduced species, but also the effect of climate change: which will have increased implications for the long-term success of reintroduction projects worldwide.

Part of In Class Assessment for Edinburgh University’s 4th Year Ecological Science Field Course, November 2012


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  15. Teixeira CP, de Azevedo CS, Mendl M, Cipreste CF, Young RJ (2007) [online] Revisiting translocation and reintroduction programmes: the importance of considering stress. Animal Behaviour 73(1):1-13. Available at: <; [Accessed November 2012]
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