The breeding ecology of the Merlin (Falco columbarius aesalon), with particular reference to north-east Scotland and land-use change
The breeding population of the Merlin in Britain in 1993 and 1994 was estimated at 1300 ±
200 pairs following a survey of around 60% of the range and calculated extrapolation of the
remaining suitable habitat. This reflected a recovery, following widespread declines in
numbers and range earlier in the 20th century. Over 1000 nest records from the survey were
analysed, with habitat and nest site described and quantified, and related to clutch size,
successful brood size and productivity. Heather moor or mixed grass-heather moor, and
tall conifer plantations were the main core habitats at 88% and 9% of territories
respectively. Habitat choice influenced nest site, with 77% of nests on the ground, 2% on
crags and 19% in trees. Productivity averaged 2.25 fledged young per pair and was
indicative of a stable or increasing population.
In north-east Scotland, part of a delimited Merlin study area was afforested with conifers,
providing an opportunity to monitor the effects of this land-use change on Merlin breeding
ecology. One of the forestry schemes led to public outcry, official objections, Government
assessment, judicial Review and an appeal to the European Commission. These events
were unprecedented in British forestry history and were seen as a test-case. Despite
modifications to the scheme, by leaving approximately 30% of land unpianted, the Merlins
declined to zero, as they also did at the other afforested areas.
Breeding phenology and clutch size at the afforested areas were similar to comparable
adjacent and further afield Merlin study areas, where there was minimal change in habitat
management. However, productivity was significantly less and it was concluded that
commercially afforested moorland was an inappropriate breeding habitat for Merlin in
north-east Scotland. Identifying and quantifying prey remains assessed breeding season
diet, with small birds accounting for 95% of numbers and 99% of biomass from 11,225
items. It is reasoned that the majority of the new potential prey resource associated with
commercial afforestation was unavailable for Merlin, due to the protection provided by
dense thicket plantations.
Guidelines for retaining breeding Merlin within commercial forestry schemes in Britain are
recommended. These could be requested by conservation planners, adopted by foresters
or tested by raptor ecologists, and their use could be a condition within new grant-aided
forestry schemes in Britain.