Monitoring occupancy of home ranges

For many species, a special licence (Schedule 1 licence, issued by SNH) is needed to visit the nest sites. This licence should be granted before any visit to a home range takes place. Those intending to ring young later in the season must be licensed and obtain their ringing permit from the BTO.

For forest-dwelling species such as Buzzard, Goshawk and Sparrowhawk, winter visits to known and suitable habitat might be useful, as the lack of leaves makes it easier to find nests in deciduous trees.

For some early-nesting species, such as Golden Eagle and Raven, visits to home ranges can start already in January, whereas for other species, especially migratory species such as Osprey, Marsh Harrier and Hobby, the first visit might occur in spring or even early summer.

The most common way of establishing whether a territory is occupied is to watch from a distance whether suitable habitat is used by hunting, displaying and nest-building raptors. This can be done from a vantage point or from a vehicle. However, raptor workers also use indirect evidence to give indications of whether a home range is occupied. This is best collected by walking through the suitable habitat looking for new and old prey remains (pluckings), moulted feathers, pellets (regurgitated fur, feathers and bones from prey animals) and faeces (normally seen as white splashes).

Once the occupancy status of the home range is established, the raptor worker normally tries to identify whether the home range is occupied by a single bird or a pair (and for a small number of species, e.g. Hen Harrier, whether a male might have more than one female) and the age of the birds in the home range. The age structure of the breeding birds in a population may give useful insights into survival of the various age groups and might act as an early signal if survival has declined for adult or sub-adult birds.

Data collected during this phase could also include habitat monitoring and should be accompanied by thorough recording of visit dates. Many raptor home ranges are likely to be unoccupied in a given year. It is important that the presence of unoccupied ranges within a study area is recorded accurately, as it will give indications of changes in the number of breeding pairs, survey effort and habitat-specific changes of occupancy.

For more detailed species-specific information please refer to Hardey et al. (2013).