20 October 2010
Image: Kevin Lewis
A small number of pairs of eagle owls are known to breed in Britain. While the origin of these birds is difficult to prove with certainty, there is no evidence that birds other than from released stock, or their offspring, have bred in Britain in recent times.
As a probable introduced species, eagle owls have been the subject of a government risk assessment to determine their likely impacts on economic interests, society and the conservation status of native wildlife.
The risk assessment concluded that an increasing population of eagle owls in Great Britain may pose a significant threat to species of conservation concern, such as hen harriers. Eagle owls are not the reason that hen harriers are absent from large parts of the UK’s uplands – that is due to sustained persecution over decades – but they do occur in places where hen harriers are hanging on.
The RSPB welcomes the publication of this risk assessment. We await Government’s response, and believe it should consult interested groups on its recommendations.
The decision as to whether a species is included on the British List rests with the British Ornithologists' Union. The BOU Records Committee compiled a dossier on the eagle owl during an assessment of its status in 1996. An extensive review revealed at least 79 reports of this species since 1684. After careful consideration, the BOU Committee concluded unanimously that many of the descriptions (where available) were not adequate to prove that eagle owl was the species concerned.
The eagle owl has been known in captivity in this country since at least the 17th century
Of those where the Committee accepted the identification as eagle owl, members were equally united in believing that the possibility of escapes and releases could not be dismissed. Nevertheless, as a European species, the eagle owl is fully protected in Britain when they occur in a wild state, unless it can be shown they were bred in captivity.
The eagle owl has been known in captivity in this country since at least the 17th century and many were brought from India during the 19th century. Eagle owls are very commonly kept in captivity - often by people who are not falconers. There is no formal requirement to register these birds, but a certificate is required if a captive bird is sold. In the 10 years to 2007, 3,370 such certificates were issued. The number of eagle owls kept in captivity is likely to be considerably higher than this.
Of the 440 captive eagle owls registered with the Independent Bird Register between 1994 and 2007, 123 (28%) were reported to have escaped. Of these, 73 were reported as not having been recovered. This equates to 9-10 escapees per annum, of which 5-6 were not recovered. If the same escape rate is applied to a conservative estimate of the British captive population over the same 13-year period, around 65 birds could be expected to escape each year.
There is some limited fossil evidence of eagle owls in Britain, and a review of these records suggests that they may have been present soon after the end of the last Ice Age. However, they appear to have died out around 9,000 years ago.
The reasons for their disappearance around this time are unclear, but the flooding of the land bridge that connected Britain to the rest of Europe may have been important. Like many owls, eagle owls disperse only short distances and find sea crossings a significant barrier to dispersal. It seems likely the English Channel prevented eagle owls from recolonising Britain.
Further evidence for their absence is provided by the cultural and historical record – despite their size and being considered a bird of ill omen elsewhere in Europe, eagle owls do not appear regularly in English or Celtic culture until relatively recently.
Eagle owls may colonise Britain in the future as the population recovers on the European mainland. If eagle owls were to arrive here naturally, the RSPB would welcome it, as we do the expansion of other colonising birds, such as little egret and Cetti's warbler.
Because those eagle owls currently breeding in Britain are very likely of captive origin, and the species has been absent from the British avifauna for a very long time, a thorough assessment of the likely impacts of its return has been undertaken. Such an assessment is needed whether the species in question has been consistently present in one part of Britain before being re-introduced to another (eg. red kites to England and Scotland) or absent for thousands of years (eg. eagle owl).
There are many examples, from this country and around the world, of serious conservation problems arising from the misguided introduction of non-native species. The introduction of American signal crayfish to many of our rivers has led our native white-clawed crayfish to the brink of extinction, while invasive plants from overseas are causing real damage to important wetland habitats in the UK. Eagle owls are a little different in that they were once native to Britain, but many thousands of years have elapsed since and the environment has changed markedly.
It is important that eagle owls breeding in Britain be monitored to understand what effect they are having
Eagle owls will prey on a wide range of birds and mammals, and they are known to be intolerant of other birds of prey and owls in their territory. Little is known about what they eat in Britain, although locally common prey such as rabbits and pheasants are known to feature. It is important that eagle owls breeding in Britain be monitored to understand what effect they are having on species of conservation concern and whether the population is expanding.
The government’s risk assessment suggests that if the population of eagle owls was to increase, the potential impact on species such as hen harriers may be significant. While the threat to hen harriers would be minimal if their population was not already suppressed dramatically by illegal killing, we are concerned by the additional pressure eagle owls may exert. It would be very unfortunate to discover in 20 years' time that eagle owls were devastating native birds, by which time it would be very difficult to do anything about it.
We therefore believe that Government should, in partnership with conservation organisations, monitor the behaviour and diet of eagle owls, and establish the true size of the wild population.
The RSPB does not support a cull of eagle owls in the UK. If intervention is deemed necessary as a result of further monitoring, non-lethal approaches, such as taking birds into captivity, should be attempted first. It is important that, in the short term, Government takes steps to significantly reduce the numbers of eagle owls escaping (or being released) from captivity. Without this, establishment of a feral population of eagle owls is much more likely.
Melling, T., S. Dudley & P. Doherty. 2008. The Eagle Owl in Britain. British Birds, 101: 478-490.
Stewart, JR. 2007. The fossil and archaeological record of the Eagle Owl in Britain. British Birds, 100: 481-486.