Action: Translocate raptors
- Six studies of three translocation programmes in the UK and the USA found that all three successfully established populations of white-tailed eagles Haliaeetus albicilla, red kites Milvus milvus and ospreys Pandion halieatus. However, the latest review of the programme to reintroduce red kites to England and Scotland reported that one of six populations was very small, with only four pairs, despite 90 birds being released.
- A replicated study in Spain found high survival and establishment of translocated Montagu’s harrier Circus pygargus fledglings.
Raptor populations across the world have been lost to persecution, pollution (e.g. DDT contamination) and other threats, and have therefore been subject to many reintroduction programmes, using both captive-bred (see ‘Release of captive-bred individuals’) and wild-bred individuals. These programmes can be controversial as large birds of prey can take livestock, but also have the potential to restore ‘flagship’ species and boost interest in conservation.
Supporting evidence from individual studies
A replicated study on the Isle of Rùm, western Scotland (Love & Ball 1979), found that, of 14 white-tailed eagles Haliaeetus albicilla translocated from Norway in 1975-7, 13 were successfully released. The remaining bird (a male) died of kidney failure after five weeks in captivitiy. Of the released birds, two (15%) were found dead but the others appear to be survive well (at least until publication in 1979). The eagles were collected at five to eight weeks old and kept for two or three months at the release site. After release, food was provided from ‘food dumps’ until the birds were able to feed themselves. This translocation programme is discussed further below.
A replicated trial (Pomarol 1994) found that, of 87 Montagu’s harrier Circus pygargus fledglings released at a marshland site in southeast Spain between 1988 and 1992, 83% successfully established in the wild (from 66% of 29 birds released in 1992 to 100% of 13 birds released in 1988-9). A further six chicks died during their first flights at the release site. Birds were taken from recovery centres (mainly chicks rescued from agricultural fields) and agricultural fields in Spanish regions with large harrier populations. They were moved to an enclosure at the release site at 20-30 days old and fed there. Five to eight days later the enclosure was opened and the birds could leave. They were then fed until they reached independence (i.e. stopped returning to be fed), an average of 30-37 days after release, depending on the age at release.
A replicated study reviewing a translocation programme for red kites Milvus milvus into southern England (Evans et al. 1998) found that translocated and newly recruited birds fledged a total of 60 young from 35 breeding attempts between 1992 and 1994. A total of 73 birds were translocated between 1989 and 1994 and first breeding was attempted (unsuccessfully) by two pairs in 1991. Five of the breeding attempts were by pairs containing at least one one-year-old bird, of which three were successful. Translocated birds came from Spain (62 birds), Wales (seven birds, taken from the wild as eggs and hatched in captivity) and Sweden (four birds). A further 20 birds from Spain were released in 1994 but their breeding attempts are not analysed here. This translocation programme is also discussed below.
A study (Evans et al. 1999) reviewed the success, until 1995, of the same red kite Milvus milvus translocation programme as Evans et al. 1994 as well as translocations to northern Scotland and found that survival and reproductive productivity were higher in England than Scotland. Between 1989-94, 93 juvenile kites (48 males, 45 females) were released in southern England and had an average first-year survival rate of 76%, increasing to 91-2% in second and third years and 100% for fourth and five years after release. There was a slight difference between male and female survival, leading to a gradual change in the sex ratio. During 1989-93, 93 juvenile kites (all from Sweden) were released in northern Scotland and had an average first-year survival rate of 52%, increasing to 67-88% in second and third years and 75-91% for fourth and five years after release. Early breeding attempts in England are described in (3) and by 1995 there were 24 breeding pairs fledging at least 115 young during 1991-5. In Scotland, breeding was first attempted (successfully) in 1992, with 15 breeding pairs in 1995. During 1992-5, 29 clutches were laid, fledging 47 chicks. Survival rates of wild-raised birds in both regions did not differ significantly from released birds during 1992-4. Main causes of mortality were poisoning and collisions in Scotland, with poisoning also being important in England.
A replicated study, reviewing an osprey Pandion haliaetus translocation programme in the Twin Cities urban area of Minnesota, USA (Martell et al. 2002), reported that a total of 143 juvenile ospreys were released by hacking (see ‘Release captive-bred individuals’) between 1986 and 1995. Breeding was first attempted in the area in 1986, with the first successful nesting in 1988. By the end of 2000, 131 nesting attempts were recorded, with 69% of them successful, producing 194 chicks in total (with an average of 1.6 fledglings/nest or 2.2 fledglings/successful nest). A small number of individuals and sites were responsible for a disproportionate number of chicks, with 85% of successful nest sites being in parks or backyards and 15% in industrial areas. This study is also described in ‘Provide artificial nesting sites’.
A 2004 review (Carter & Newbery 2004) of the same red kite Milvus milvus translocation programmes to the UK as in (3,4) found that the release of 518 subadult birds (between 69 and 103 at each site) between 1989 and 2004 resulted in the establishment of one population of at least 177 breeding pairs (from 93 birds released), four populations of between 16 and 35 breeding pairs and one population of just four pairs (90 birds released, beginning in 2001). Productivity in 2003 was comparable to other parts of their range (1.8-2.0 young/breeding pair) for all populations except the smallest (0.25 young/breeding pair). High mortality rates in the less successful sites are thought to be due to illegal poisoning. Birds were taken from large populations across Europe when 4-6 weeks old, kept in aviaries for a further eight weeks (with minimal human contact) and then released. This paper also discusses the release of captive-bred corncrakes Crex crex, discussed in ‘Release captive-bred individuals’.
A 2009 review of two white-tailed eagle Haliaeetus albicilla translocation programmes in western Scotland (Evans et al. 2009) found that the release of 82 individuals in 1975-85 and 59 in 1993-8 led to the establishment of a population of 42 territorial pairs in 2007, with the number of territorial adults increasing at 9.7%/year during 1997-2007. Survival rates of released birds were significantly lower than those of wild-bred birds, particularly during the first three years of life (74% survival for one year-old released birds vs. 82% for wild-bred; 94% survival for released birds aged four or more vs. 97% for wild-bred birds; overall probability of surviving until five years old of 37% for released birds vs. 53% for wild-bred). Breeding success of the established population is similar to that of the Norwegian population (in similar environmental conditions) but lower than populations elsewhere in Europe. Overall, breeding success and productivity have increased with time, as reintroduced birds get older (which significantly increases the probability of fledging young) and a higher proportion of the population consists of wild-bred birds (0.61 young fledged/territorial pair in 1993-2000 vs. 0.76 young fledged/territorial pair in 2003-7).
- Love J.A. & Ball M.E. (1979) White-tailed sea eagle Haliaeetus albicilla reintroduction to the Isle of Rhum, Scotland, 1975-1977. Biological Conservation, 16, 23-30
- Pomarol M. (1994) Releasing montagu's harrier (Circus pygargus) by the method of hacking. Journal of Raptor Research, 28, 19-22
- Evans I.M., Cordero P.J. & Parkin D.T. (1998) Successful breeding at one year of age by red kites Milvus milvus in southern England. Ibis, 140, 53-57
- Evans I.M., Summers R.W., O'Toole L., Orr-Ewing D.C., Evans R., Snell N. & Smith J. (1999) Evaluating the success of translocating red kites Milvus milvus to the UK. Bird Study, 46, 129-144
- Martell M.S., Englund J.V. & Tordoff H.B. (2002) An urban osprey population established by translocation. Journal of Raptor Research, 36, 91-96
- Carter I. & Newbery P. (2004) Reintroduction as a tool for population recovery of farmland birds. Ibis, 146, 221-229
- Evans R.J., Wilson J.D., Amar A., Douse A., MacLennan A., Ratcliffe N. & Whitfield D.P. (2009) Growth and demography of a re-introduced population of white-tailed eagles Haliaeetus albicilla. Ibis, 151, 244-254