This project conducted preliminary investigations into the demography and population dynamics of Welsh hen harriers Circus cyaneus, using historical data from population surveys, nest visits, and a programme of wing tagging nestlings in 1990-1995. Initial emphasis was on collating and reviewing existing data, deriving estimates of demographic parameter values and conducting exploratory population modelling. Sample sizes for estimation of several demographic parameter values through resightings of wing tagged birds were limited, inevitably with a relatively small Welsh ‘population’ and because collation of resighting records declined after tagging stopped in 1995.

The Welsh harrier ‘population’ appeared to be relatively stable for much of the late 1980s and 1990s, before increasing in the 2000s. Estimates of breeding productivity and breeding success were derived across several years and were largely similar to previously published estimates. Predation and human interference were the most commonly recorded causes of breeding failure. Interference was associated with nests on ground where gamekeepers were employed, but appeared to cease in the late 1990s onwards, concomitant with an increase in both productivity and population abundance. Predation appeared to show no association with the presence or absence of gamekeepers, and was not obviously related to recent changes in productivity and population abundance. Population modelling through Leslie (population projection) matrices suggested that the Welsh female harrier ‘population’ was probably capable of ‘self-sufficiency’ although some connectivity with other breeding areas, through natal dispersal, was evident. Population projections for males based on observed demographic rates indicated that the male population should be declining rapidly or was heavily reliant on immigrant males from outside Wales, even when accounting for many potential estimation biases: observations suggested that the population was not declining. The most likely explanation of these disparities was that natal dispersal in males was substantially greater than in females. In other words, the effective male population extended well beyond Welsh breeding areas and the effective female population.

Principal Investigator: P. Whitfield

Collaborators: A. Fielding, Manchester Metropolitan University

Client: Countryside Council for Wales (CCW)

Photos: M. McGrady and D. Jackson

For more information please contact phil.whitfield@natural-research.org