Use of dwarf shrubland–grassland mosaics by a nomadic predatory bird, the Short-eared Owl Asio flammeus

A substantial proportion of Britain’s Short-eared Owl population breeds on managed moorland, where these avian predators specialise on small mammal prey. Such moorland is widely managed for Red Grouse through the control of predators and the burning of vegetation, practices which can be controversial. Efforts to increase or restore heather and other dwarf-shrub cover, which are seen by many as a conservation priority, may also alter the nature of the moorland habitat used by Short-eared Owls.

Set against this background, it has become especially pertinent to understand how Short-eared Owls use moorland habitats and, in particular, the different vegetation types present. Because of their nomadic behaviour, there is also a need to understand how these birds use similar open habitats elsewhere. This tracking study, which involved 17 fully-grown Short-eared Owls tagged with GPS tracking devices in Scotland between 2017 and 2020, provided an opportunity to look at individual habitat use across the different sites used by these birds in Scotland, England and Norway.

The study looked at habitat use within individual home ranges, i.e. those areas used by the birds for more than five consecutive days and which were less than 500 hectares in size. Locations within 50 m of nest sites were excluded from the analysis because females may continuously incubate eggs or brood small chicks, skewing attempts to understand habitat use. 

Relative to their availability, there was a tendency for Short-eared Owls in Britain to preferentially use areas of grassland, including those smaller patches located within a wider Heather-grassland mosaic. In contrast, the tracking data from those individuals that also spent time in Norway revealed a tendency to hunt more over dwarf shrubs. The dwarf shrub community in Norway is more diverse than here in Britain, both in terms of species composition and structure. Such differences are likely to reflect prey availability, but they also highlight the behavioural plasticity of these birds.

The results of this work can be used to inform relevant conservation strategies in at least three different ways. They inform the habitat management of specific sites, highlight landscapes towards which targeted management could be directed, and identify specific sites for conservation designation, protection and management.

Notes

We thank the many individuals who have help find and tag owls and discussed ideas, and the landowners and managers who have granted access for fieldwork. Particular thanks are due to Dave Southall, Terry Southall, John Fitzpatrick, Jean Fitzpatrick, Alex Penn and Colin Shand for their help with fieldwork. Funding and other support was from many individual donors, the Abertbrothock Skea Trust, AEB Trust, Arran Natural History Society, British Birds Charity, Callander SWT group, DOPP (BirdLife Slovenia), Gilman Trust, the Henry Robb bequest, J & JR Wilson Trust, Loch Lomond Bird of Prey Centre, Muncaster Castle, NBI Ljubljana, Newstead Charity, Sound Approach, Stirling SOC group, Tan International, Tayside Raptor Study Group, Tay Ringing Group, to all of whom we are most grateful. We thank two anonymous reviewers for their comments improving the manuscript.