Wednesday, 10 December 2008

Short-eared Owls sweep the marshes

The Short-eared Owl is one of our most enigmatic birds; a scarce breeding species that favours some of our more remote and wild places. It is one of those birds that you cannot really expect to see every year without a degree of luck or a certain amount of effort. The Short-eared Owl can justifiably be described as a nomad, its breeding range extending across much of the Northern Hemisphere, from North America and Iceland, across Europe and Asia to the Pacific. There are even isolated populations in South America, on the Falkland Islands and, incredibly, the Galapagos. Young birds from the British breeding population have been found in Ireland, Spain, Malta and even Russia, further emphasising their nomadic nature.

It is fluctuations in the populations of their favoured small mammal prey, predominantly voles, that can drive these nomadic movements. In years when voles are plentiful, the owls have a good breeding season and produce lots of young. If the abundance of voles then declines so the owls are forced to wander more widely in search of prey. Some idea of the influence of small mammals in driving the numbers of owls recorded within Norfolk can be seen from a count of 116 roosting together along the Fleet wall at Halvergate in December 1972; the following winter saw just three birds in the same area.

One of my most enduring memories as a birdwatcher is seeing Short-eared Owls arrive in off the sea during autumn. These were likely to have been Scandinavian birds, given the location, but many of those wintering within the county will have come from breeding populations located in the uplands of northern Britain (from the Peak District north into Scotland). Newly arrived birds may remain on the coast, hunting over salt- and grazing-marshes, but they may also range widely, visiting farmland and inland heaths. As well as taking small mammals, the owls will also turn their attentions to small birds, particularly those species that roost or feed communally. Studies of Short-eared Owl diet have highlighted the importance of Dunlin, Skylark, Starling and Ringed Plover. Many individuals seem to take what is available but some individuals show a degree of specialisation, targeting one particular species, such as Brown Rat.

Hunting Short-eared Owls work an area in a similar manner to a hunting Barn Owl, quartering the ground for prey. Unlike the Barn Owl, however, the Short-eared will readily roost on the ground or in low scrub. Over the last few weeks at least two Short-eared Owls have been hunting over the grazing marshes just east of Lady Ann’s Drive at Holkham. Others have been reported from the Broads and the Fens.

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