Eagle owls – are they making a comeback in Britain?

Recent news (here and here) that a pair of eagle owls are preparing to nest in North Yorkshire has restarted the controversy around one of the largest owls in the world.

Eagle owls - in Britain?

The Scots Gaelic, Manx, Welsh, Cornish and Irish Gaelic languages all have words for them and it is generally agreed that fossil records indicate eagle owls were present in Britain from some 700,000 years (to at least 10,000 years ago but the evidence for more recently presence is inconclusive). – ten times longer than anatomically modern humans.

There are currently claimed to be 12-40 pairs of eagle owls nesting in Britain but no one is certain how many of these have escaped from captivity (eagle owls were used as decoys to catch birds such as the magpie for centuries) and how many have naturally immigrated here from Europe.

We know that the smaller long-eared and short-eared owls regularly migrate to Britain from Scandinavia and either pass through or stay for the winter (especially the long-eared owl). Owls have been seen resting temporarily on oil rigs in the North Sea. This would explain why some ornithologists were not surprised that isotope analysis of an eagle owl found in Norfolk ten years ago indicated overseas origin.

Are eagle owls native to this country?

The historic records from Orkney (1830), Shetland (1863, 1871) and Argyll (1883) seem likely to be genuine, but the British Ornithologists’ Union (BOU) concluded that these and other records were not strong enough (to reach a balance of probability which is overwhelmingly in favour of natural immigration) and so have classified it as non-native. The World Owl Trust has called for the BOU ruling to be reversed and offered supporting evidence as to why it believes the eagle owl is, and always has been, a true native British species.

Are they protected by law?

All wild bird species (native or non-native) are fully protected by the Wildlife & Countryside Act (remember that offspring of birds that have escaped from captivity are considered wild birds). Any intervention (to cull or remove them to captivity to protect native species, etc) may require a licence from Natural England, if they felt eagle owls were protected by the Act.

Such a licence might be issued more swiftly if it is to control a non-native species – so the status of eagle owls is important. The RSPB has previously said it would not support any cull of eagle owls in Britain, but some will be wondering why the RSPB has begun comparing them to escaped American mink, which are controlled.

Should they be compared with American mink?

American mink were brought here by man relatively recently and can have a devastating effect on local wildlife. On the other hand, eagle owls have lived alongside our other native species for hundreds of thousands of years, so many might consider it alarmist to compare the two. Some may compare them to beavers, which have been reintroduced to this country, but this could also be unfair because eagle owls may be arriving here naturally – just as they are believed to have done in Holland and Belgium.

Where else are they making a comeback?

This top predator is also making a comeback following reintroductions in Norway, Sweden, Switzerland, France, Belgium and Germany. These recovery programmes have received wide acclaim for recovering a species that underwent a significant decline across Europe, along with other top predators such as the wolf and lynx, mainly due to human persecution. Recently, this species has started to colonise urban habitats and is now breeding in several towns and disused quarries in Europe.

Are they a threat to other wildlife?

Eagle owls mostly eat rodents (voles) and Lagomorphs (rabbit and mountain hare, but will also take mustelids, foxes and occasionally fawns. In this country the eagle owl’s main prey appears to be rabbits.

Among birds the most common species eaten are woodpigeons and corvids, and they take a range of water birds. Among the avian predators, though, it is one of the most likely to kill other owls and raptors. The most common raptor in the diet is considered to be the buzzard.

They also take a wide range of other mammals and birds, including raptors; however, the overall impact is unclear. In Bowland, for example, where eagle owls have nested, some other birds of prey continued to nest in the area. In Europe they have been observed killing young and adults of almost all raptors, up to the size of (and including) female goshawks. They are believed to kill for both food and nest defence (they dislike raptors nesting nearby).

Some eagle owls may specialise in killing raptors; one pair in Norway was reported to have killed 13 raptors and owls in one nesting season. In Germany, where the eagle owl has recolonised there is clear evidence of substantive adverse effects on the breeding success of goshawks and buzzards.

In 2010 an eagle owl was caught on film predating a hen harrier. Other species of conservation concern they are known to predate include pine martens, capercaillie, and various raptors and owls

Are they a threat to humans or domestic animals?

They may be aggressive towards people within the breeding territory. This includes some European cities. The species has also believed to take cats and dogs. They have also been known to take lambs, although this appears to be rare

So should we be ‘nipping this in the bud’?

This phrase may be unhelpful. Buzzards are far more numerous than eagle owls in this country, where they are known, for example, to take tawny owls and kestrels. Should we be nipping buzzards in the bud too?

Any studies on gamebird species?

In one particularly detailed study of eagle owl diet, partridges accounted for 8.4% of items and pheasants for 2%, with potential egg predators accounting for over 31% of items. The most important egg predator, the hooded/carrion crow, features in eagle owl diets more than twice as often as in goshawk diets.

Gamekeepers will also be interested to hear that, in the USA, scientists noted that the similarly sized great horned owl had such a great effect on nesting crows that their density is low compared to Britain. These top predators can have other impacts. Scientists in Finland concluded that the golden eagle and wolves could have beneficial effects on small game because they might reduce the need for gamekeepers to control medium-sized carnivore populations including as foxes and mustelids.

Are they prone to disturbance?

Eagle owls are thought to be highly sensitive to disturbance, particularly during incubation, as it may cause adults to abandon eggs and even small young. In Bowland disturbance by licensed raptor workers has been seen by some as the main problem faced by eagle owls.

Does it have any natural enemies?

Only white-tailed eagles and golden eagles are known to kill eagle owls but badgers, pine martens and foxes might predate eagle owl nests. Their populations may be limited by the availability of nest sites. There is some evidence from central Europe to support this.

What next?

This is a species that has had to overcome persecution, the accumulation of pesticides up the food chain, and collisions with vehicles, barbed wire and power lines. The British Trust for Ornithology states that they have bred here for 20 years – so coupled with its expansion across continental Europe, this species appears to be winning against all odds.