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Barn owl scoping survey
A barn owl scoping survey involves inspecting a building, tree or any other structure that could support nesting or roosting barn owls for evidence of barn owl activity i.e. regurgitated pellets, moulted feathers, and white wash (barn owl droppings) found under roost or nest sites on the ground, on walls or tree trunks.
Nesting barn owls do not build a nest as such but will use a ledge in a building, a cavity in a tree or a similar feature where they lay their eggs on a cushion of pellets the female has actively shredded.
The survey therefore involves identifying features in buildings, trees or structures that barn owls could use as a nest or roost site and searching for evidence of use by barn owls. A barn owl scoping survey also involves assessing the suitability of surrounding habitat and obtaining local records of barn owl activity, and this can be undertaken as part of a Preliminary Ecological Appraisal.
Habitat assessment for barn owls
The potential value of an area to barn owls in terms of prime foraging and dispersal habitat can be determined most reliably and efficiently by identifying and recording the type, size and distribution of grasslands present.
Barn owls require prey-rich rough grassland habitat over which to hunt where they feed primarily on small mammals, mainly field vole, as well as other species of vole, mice, shrews and young rats. These habitats are unmanaged permanent or semi-permanent grasslands that possess a tussocky structure and a deep matted blanket of dead grass stems at their base beneath which small rodents can nest, move and feed in comparative safety.
Barn owl activity (observational) surveys
Where there is potential for barn owl to be physically harmed by development or an activity e.g. a proposed wind turbine or new road scheme, or where there is to be significant loss of key foraging habitat, such as to a large-scale residential development, it may be appropriate to map barn owl flight activity in addition to identifying the location of nest and roost sites within a study area.
Vantage Point surveys can be used to map barn owl flight activity. They rely on the observation and identification of birds in flight and can be used to define the home ranges of individual birds, the flight heights they adopt and also the places which are used by them for foraging and movement. The location of any nearby nest or roost sites will also need to be established during a barn owl scoping survey.
Timing of surveys
- Barn owl scoping surveys can be undertaken at any time of year and as part of a Preliminary Ecological Appraisal although assessment of trees may be best in autumn, winter or early spring when most trees are devoid of foliage and associated habitat features are most visible and accessible. For suspected nest sites it may be necessary to avoid direct disturbance during sensitive nesting times, generally between March and May, when barn owls may be in the process of selecting their nest sites or laying eggs;
- Habitat surveys can be undertaken at any time of year and as part of a Preliminary Ecological Appraisal;
- Barn owl activity (observational) surveys are best undertaken during the late breeding season, generally between mid-June and late-July although surveys can extend into October to take account of second or late broods.
Mitigation
Mitigation may include sensitive timing of works to avoid the breeding season (barn owls generally breed between February and August) or the setting of Protection Zone Distances whereby particular activities are excluded, sometimes up to 175m from an active nest site.
Providing barn owl boxes, lofts or purpose-built towers is appropriate when barn owl nest or roost sites will be lost, with birds given a minimum of 30 days to find and hopefully adapt to their new nest site.
A reduction in food availability is the principle cause of barn owl population decline and therefore habitat improvement is the most important conservation measure. If key foraging habitat is to be lost then providing alternative habitat, either through new planting or enhancing existing habitat to that of permanent rough tussocky grassland will ensure that barn owls have a consistent food supply.
Legislation
All wild birds are protected primarily through the Wildlife and Countryside Act (WCA) 1981 (as amended). This makes it an offence to:-
- Intentionally kill, injure or take any wild bird;
- take, damage or destroy a nest (whilst in use or under construction);
- take, damage or destroy its eggs; or
- possess wild birds (dead or alive) or their eggs.
Barn owls are also protected under Schedule 1 of the WCA (as amended), which gives them additional protection i.e. ‘the intentional or reckless disturbance whilst nest building, at a nest containing eggs or young, or disturbing dependent juveniles’ is an offence.
Note
The above information is based on standard guidelines and current UK legislation. Every site is unique so please contact a Torc Ecology consultant who will advise on the best survey approach in relation to the project requirements.
