The Hen HarrierCircus cyaneusWinter Roost Survey in Britain and Ireland

The size and migratory origins of the population of Hen HarriersCircus cyaneuswintering in England

“…Clarke and Watson (1990) noted that between the mid1970s and the late-1980s 67% of all Scottish ringing recoveries from October-March had been in Scotland itself, a general picture also found in this current analysis. However, Clarke and Watson (1990) inferred that this meant that there would be too few harriers to make up a large proportion of the wintering population in England, but the results of the present study suggest otherwise.…”

“…However, Clarke and Watson (1990) inferred that this meant that there would be too few harriers to make up a large proportion of the wintering population in England, but the results of the present study suggest otherwise.…”

“…It should be concluded, therefore, that the HHWRS must be expanded to include a larger proportion of harrier roosts, and population estimates drawn from the HHWRS should be calibrated by an additional stratified random survey of potentially suitable unsurveyed sites in order to quantify the number of birds routinely missed by the standard survey. Clarke and Watson (1997) thought it likely that the survey did not encompass even the majority of sites in Scotland, though the same authors previously estimated that 80% of English communal roost sites were covered in the early 1980s, and adjusted the survey results accordingly (Clarke & Watson 1990). Unless the total number of non-British winter immigrants to England did not exceed about 30 individuals, this claim appears to be overly optimistic.…”

“…These values were compared with published winter population estimates for England (taken from Clarke [in Lack 1986] and Clarke & Watson [1990]). Clarke's (in Lack 1986) estimate of 300 wintering Hen Harriers in England is assumed to be based upon early 1980s (or earlier) data; Clarke and Watson (1990) estimated that the midwinter population in England peaked in the winters of 1983/84 and 1984/85 at 400. A mean value of 350 for the 1980s was, therefore, considered reasonable.…”

“…In Q 2012 British Trust for Ornithology, Bird Study, 59, 218 -227 order to be broadly aligned with Clarke's (in Lack 1986) and Clarke & Watson's (1990) winter population estimates, population and productivity data from as close to the 1980s as possible were used in preference to the most recent censuses, though accurate national-scale productivity data for Great Britain (excluding Orkney) were only available from relatively recent studies. Population sizes for Orkney and the rest of Great Britain were calculated separately to take advantage of greater precision of estimates for the former.…”