Scottish Raptor Groups - Short-eared Owl

Amongst the owls found in Britain, the Short-eared Owl is one of the most active during daylight hours. Despite this, and its charismatic appeal, current numbers and population trends are poorly known. An estimate of the Scottish population suggests 780 - 2,700 breeding pairs, with an estimate for the U.K. of 1,000 – 3,500 pairs in the early 1990s: although this is acknowledged to be one the most unreliable estimates for any raptor or owl species (Greenwood et al. 2003). Breeding numbers are known to fluctuate markedly in response to prey availability (e.g. Village 1987, Petty et al. 2000) and the birds are believed to range quite widely. This variation in abundance has no doubt added to the difficulty in assessing the numbers of breeding Short-eared Owls in Britain and any recent population trends.

In Scotland, most breeding Short-eared Owls are associated with moorland the highest densities reported from rough grasslands adjacent to, or intermixed with, heather moors (marginal hill ground or ‘white moor’). Young conifer plantations can also be important habitats, though second and later rotation plantings are perceived to be less used than initial plantings. A reduced availability of young first rotation planting on moorland may have contributed to a reduced area suitable for breeding in some regions and probably resulted in an overall population decline. Therefore, numbers currently breeding in Scotland could be lower than suggested above.

Lowland rough grassland, marshes and coastal sand dunes are also used for breeding though their use of such areas can be erratic, except on some of the western islands and Orkney. Published territory sizes of breeding Short-eared Owls in Britain range from one territory per 40 hectares to one per 875 hectares (Calladine et al. 2005). Elsewhere in Europe, breeding Short-eared Owls can be found in relatively intensive agricultural areas including cereal crops, meadows and rye grass fields, though this probably reflects a different prey base to that found in Britain. In Britain, a major prey item is the Short-tailed Field vole, though other small mammals can be important, notably on islands where voles are absent or where alternative prey is available, for example, Common Voles in Orkney (Glue 1977).

In winter, when many upland areas are abandoned, the species is mostly found in marshes and coastal grasslands. Ringing recoveries suggest many Short-eared Owls seen on the east coast in autumn probably originate from Scandinavia (Glue 2002) with some of these birds remaining for the winter. In north-east Scotland, high breeding densities are reported as often being preceded by influxes at the coast in the previous autumn (Buckland et al. 1990). Other ringing recoveries also suggest movements between countries further south and east in Europe. The degree and nature of connectivity between birds that breed in Britain and elsewhere in Europe is unclear.

John Calladine

References

Buckland, S.T., Bell, M.W. & Picozzi, N. 1990. The Birds of north-east Scotland. North-east Scotland Bird Club, Aberdeen.

Calladine, J., Crick, H. & Wernham, C. 2005. Development of methods for surveying and estimating population size of short-eared owls. A report to Scottish Natural Heritage. BTO Research Report No. 394, BTO Scotland, Stirling.

Glue, D.E. 1977. Feeding ecology of the Short-eared Owl in Britain and Ireland. Bird Study, 24, 70-78.

Glue, D.E. 2002. Short-eared Owl. In Wernham, C.V., Toms, M.P., Marchant, J.H., Clark, J.A., Siriwardena, G.M. & Baillie, S.R. (eds) The Migration Atlas: movements of the birds of Britain and Ireland. T. & A.D. Poyser, London. Pp 437-440.

Greenwood, J.J.D., Crick, H.Q.P. & Bainbridge, I.P. 2003. Numbers and international importance of raptors and owls in Britain and Ireland. In: D.B.A.Thompson et al, eds. Birds of Prey in a Changing Environment. Edinburgh, The Stationary Office. pp. 25-49.

Petty, S.J., Lambin, X., Sherratt, T.N., Thomas, C.J., Mackinnon, J.L., Coles, C.F., Davison, M. & Little, B. 2000. Spatial synchrony in field vole Microtus agrestis abundance in a coniferous forest in northern England: the role of vole-eating raptors. Journal of Applied Ecology, 37, 136-147.

Village, A. 1987. Numbers, territory size and turnover of Short-eared Owls Asio flammeus in relation to vole abundance. Ornis Scandinavica, 18, 198-204.