This falcon is very much an inhabitant of open country throughout the year, occupying Britain’s uplands during the breeding season – mainly March to late July – and farm and coastal country outside this period wherever small passerine prey is available.
Nests are by preference sited on the ground in stands of degenerate heather, ideally surrounded by a mosaic of varying stage-of-growth ling beds and burns – a combination to be found principally on grouse moor estates where heather-burning regimes are practised. In areas where suitable heather stands are not available birds will resort to tree-nesting in old crow nests. Meadow Pipits in most breeding areas provide the bulk of the prey taken there although there is evidence in some areas of a decline in numbers of this species with Merlins having to seek more moorland – edge and forestry prey. The male bird provides the bulk of the food for female and brood throughout the nesting cycle. Egg-laying, normally a clutch of 4, occurs over late April early May, incubation is about 28-32 days with young fledging after a similar interval. Most will continue to frequent the nest site for a week or two before dispersing some to considerable distances, occasionally even to the Continent.
Status and range
The bulk of the UK breeding population is to be found in Scotland and northern England. The RSPB carried out a partial breeding survey of the species over 1983/84 and estimated the national population to be in the order of 550-650 pairs. A national survey in 1993/94 revealed virtually a doubling of breeding stock to c.1300 pairs. It was considered at the time that the increase although valid in major part, was contributed to by pairs in Wales that had switched from ground to tree nesting due to habitat degradation, had gone undetected and did not feature in the 1983/84 survey figure. A third national survey in 2008 however, although indicating population estimates for Britain and northern England were only slightly down on those of 1993/94, did reveal marked declines in some regions of the latter – 69% in Northumbria and 47% in both the North York Moors and South Pennine populations. Overall the estimate for northern England was 25% lower than that of the 1993/94 survey. Historically, there has always been a very small population in the south-west of Britain but with only one pair recorded in the 2008 survey it must be bordering on imminent extinction.
Threats and concerns
As with most raptors the species has recovered well from organochlorine pesticide poisoning over the 1950/60’s. Nonetheless addled eggs and corpses of Merlin are routinely tested for such poisons along with other birds of prey at the Centre for Ecology and Hydrology, Lancaster. Shooting and egg collecting/brood-robbing are problems still with us though not to any worrying extent. Perhaps the aspect of Merlin biology which most concerns raptor workers in some areas is the decrease in numbers of principal prey items such as Meadow Pipits, Skylarks and Starlings which can affect survival rates of young. Another trend of the last few years that has serious potential implications for the welfare of chicks is that of unseasonal heavy rainfall – some spells of which can last for hours sometimes days. If these occur when chicks are still in down and too big to be brooded effectively, death is likely to ensue from hypothermia. Overall, the future does not look too rosy for the species in northern England. If global warming continues apace, the Merlin as a sub-Arctic species might well be forced eventually to retreat northwards leading to the extinction of populations on the southern limit in of its geographical range in Britain.