Status of the Great Grey in Britain and Ireland

Peter Fraser and John Ryan

The excubitor is a widespread Holarctic . The nominate race breeds from Scandinavia and France east to western Siberia, northern populations exhibiting a winter dispersal or short-distance migration to warmer areas, including Britain and Ireland (Cramp & Perrins 1993). Its status in these last countries has not been investigated in detail until comparatively recently. This paper attempts to estimate the current numbers of this attractive shrike visiting these islands.

Historical perspective In the first half of the twentieth century, when there were far fewer observers than there are today, records of Great Grey Shrike in Britain seemed to be rather scarce. Bannerman (1953) suggested that the Great Grey Shrike might be 'even [an] annual visitor to our shores'. Two decades later, it was described as both a passage migrant and a winter visitor in 'small, rather variable numbers', being most numerous on the East Coast in October, with most wintering individuals occurring in Scotland (BOU 1971). The first systematic attempt to assess the British wintering population was made during 1981-84, with the Winter Atlas (Lack 1986): records were found to be much more widespread in midwinter than had previously been supposed, and the wintering population was estimated at a minimum of 150 individuals. In Britain, the Great Grey Shrike has long been characterised by considerable annual fluctuations in its numbers. The available records nevertheless suggest that there has been a general decline over the last 40 or more years, and particularly since the 1970s. Several previous traditional wintering areas, such as in Hampshire (Clark & Eyre 1993) and south Staffordshire (R. A. Hume in litt.), are no longer being occupied by Great Grey . The evidence from Scotland

478 [Brit. 88: 478-484, October 1995] © British Birds Ltd 1995 British Birds, vol. 88, no. 10, October 1995 479 also suggests that the species is less common than formerly in that country: a total of over 140 autumn records in 1970 (with at least 70 individuals overwintering) had dropped to around 100 in 1982 (Thom 1986). The species remains a great rarity in Ireland, with a total of only 13 recorded during 1966-86 (Hutchinson 1989). Only one was discovered in Ireland during survey work for the Winter Atlas (Lack 1986).

Methods In order to make a quantitative assessment of the numbers and distribution of Great Grey Shrikes in Britain & Ireland in winter, we searched all local, regional and national reports for the years 1986-92 and extracted all records of the species. A total of some 890 published records was collated and analysed, and their distribution plotted according to vice-counties. The records were initially classified into three groups: (i) site-faithful long- staying wintering individuals; (ii) short-staying East Coast autumn migrants; and (iii) all other records. Predictably, those records which fall into the third group posed the biggest analytical problems. Of the 890 records, 534 (60%), a much higher percentage than might be suspected, referred to individuals seen on one day only. These could fall into any of the three groups; most are autumn migrants (see below), but they also include individuals on well-known wintering sites which were seen only intermittently, as well as 'one-off records at other localities. In estimating the wintering population, we started with those individuals which were long-staying territory-holders, which we defined as those recorded staying for longer than ten days. In addition, we included those shrikes which, although seen for as little as just one day in the winter (December-February), were observed regularly in the same area in more than one year in the period under review. These records indicate that individuals were probably resident in the area, but were being under-recorded. The remaining records (the vast majority) are of short-staying individuals not associated with regular wintering areas. We categorised these as follows: 1. Individuals recorded before December, seen for less than ten days and away from known wintering territories: these are mostly coastal migrants. 2. Individuals recorded in December-March inclusive, seen for less than ten days and not on a regular basis from year to year: these we have called 'winter wanderers'. 3. Records in spring/summer from April onwards.

Results and analysis The annual totals for each category are shown in table 1. The figures are calculated for each winter period (i.e. autumn to spring) rather than for each calendar-year. The four different categories are considered separately below.

Winter residents During 1986/87-1991/92, the number of Great Grey Shrikes wintering in Britain ranged from 28 to 51, with a mean annual figure of 37 (table 1). The two years with the highest number of individuals overwintering (1988/89 and 1990/91) 480 Fraser & Ryan: Great Grey Shrikes in Britain and Ireland

Table 1. Total numbers of Great Grey Shrikes Lanius excubitor recorded in Britain and Ireland, 1986/87-1991/92.

Category 1986/87 1987/88 1988/89 1989/90 1990/91 1991/92 Mean

Winter residents 38 30 43 30 51 28 37 Autumn 38 36 71 29 70 70 52 Winter wanderers 18 17 21 19 29 22 26 Spring 18 9 29 9 10 1 13

Totals 112 92 164 87 160 121 followed the 'best' autumns. Large autumn numbers do not, however, necessarily produce a large wintering population, as demonstrated by, for example, winter 1991/92. The distribution of winter residents is shown in fig. 1. The New Forest, Hampshire, has the highest number of wintering Great Grey Shrikes in Britain. The next most favoured areas are, in approximate order of importance, the Dartmoor and East Devon commons area of south Devon, the Surrey heaths, Rauceby Warren in south Lincolnshire, and Kielder Forest in south Northumberland. Other important areas include the Loch Ken area of Kirkcudbrightshire in Galloway, Budby in Nottinghamshire, Breckland on the west Norfolk/west Suffolk border, and the Lee Valley area of Hertfordshire.

Fig. 1. Distribution in Britain, by vice- Fig. 2. Distribution in Britain, by vice- counties, of site-faithful, long-staying counties, of short-staying Great Grey Great Grey Shrikes Lanius excubitor in Shrikes Lanius excubitor in autumn, 1986- winter, 1986/87-1991/92. 92. British Birds, vol. 88, no. 10, October 1995 481 Great Grey Shrikes have a catholic taste in habitat. The most favoured areas in the south coincide with the lowland-heath habitat preferred by the Red-backed Shrike L. collurio in its last decades as a breeding species in Britain, but young coniferous plantations are also popular. Otherwise, they occur in almost any habitat that is exposed and open, with sparse trees and bushes to allow vantage points.

Autumn passage An annual average of 52 individuals was recorded in autumn, their distribution being shown in fig. 2. The majority of autumn records are from the East Coast, with most from east and west Norfolk, southeast Yorkshire and the Northern Isles of Scotland. This pattern is typical of scarce migrants breeding in Fenno-Scandia, such as Icterine Warbler Hippolais icterina, Barred Warbler Sylvia nisoria and, especially, Greenish Warbler Phylloscopus trochiloides. It seems reasonable to assume, therefore, that most Great Grey Shrikes reported at this time of year are passage migrants. The most frequented sites in October and November are at the major East Coast migration stations: Spurn in southeast Yorkshire had a total of 15 records during 1986-92, followed by Flamborough Head with 11 and Fair Isle with nine. Of interest in assessing the winter population is the number of records away from the coast in areas unfashionable for migrants. As mentioned above, the category 'autumn' does not include those individuals recorded in October and November in regular wintering areas (these are included within 'winter residents'). Of a total of 352 individuals recorded over seven autumns (1986-92), 230 were seen at migration watchpoints, leaving 122 observed elsewhere (an average of 17 per year). It may seem reasonable to call these latter birds casual winter visitors or 'winter wanderers' which, through lack of coverage or high mobility, are not knowingly recorded subsequently. Nevertheless, some of these must be genuine migrants. Somewhat arbitrarily, we have split this group into two, giving mean figures of 42 migrants and nine winterers. The timing of the autumn migration of the Great Grey Shrike is shown in fig. 3. We have used data from the Northern Isles only, as this minimises the risk of the figures being distorted by the presence of irregularly observed winter residents. Of the 75 individuals involved, 55% (41) were recorded in October and another 16% (12) in November, with the peak in the last week of October.

Fig. 3. Autumn migration of Great Grey Shrikes Lanius excubitor in Northern Isles, Scotland, 1986-92. The period concerned, in seven-day periods, is week 36 to week 52 (records from week 39 to week 48), with peak during 22nd-28th October. 482 Fraser & Ryan: Great Grey Shrikes in Britain and Ireland Throughout Britain, the species is extremely rare before the last week of September; during 1986-92, there were records of one individual arriving in July (Hoy, Orkney, 5th July 1991), one in August (Flamborough Head, 29th-30th August 1991) and two in the first half of September (Bere Regis, Dorset, 9th September 1990; Holme, Norfolk, 11th September 1989). It might be anticipated that coastal sites would provide incontrovertible evidence for the continuing arrival of Great Grey Shrikes throughout the winter, but this is not the case. In the Northern Isles, there were records from Shetland (Channerwick, 4th January 1992) and Orkney (North Ronaldsay, 22nd February 1986); despite many winter records for coastal Norfolk, there was none for the Yorkshire 'migrant traps'. A correlation of high autumn numbers with high wintering numbers does not necessarily imply that individuals seen on the East Coast in October are the same as those seen inland later in the winter. The disparity between the autumn and winter figures in 1991/92 may in fact indicate otherwise. A successful breeding season could well produce the same effect, with the October migrants subsequently moving on to overwinter in southwest Europe.

Winter wanderers Included in this category is a smaller number of individuals (annual mean 26) seen for only a short duration in the winter period (fig. 4). Their contribution to the general statistic is very difficult to assess. In Scotland, there is a disproportionately high number of records in this category, which would imply that wintering shrikes are under-recorded.

Fig. 4. Distribution in Britain, by vice- Fig. 5. Distribution in Britain, by vice- counties, of transient Great Grey Shrikes counties, of Great Grey Shrikes Lanius Lanius excubitor in winter, 1986/87-1991/92. excubitor in spring, 1986-92. British Birds, vol. 88, no. 10, October 1995 483

Alternatively, some of the records could arise from shrikes wandering from known territories; or could include a completely unknown number of individuals showing facultative migration from the Continent during the winter. This last theory is possibly supported by the large number of records in Norfolk, where the level of observer coverage would lead to a higher percentage of winter residents being discovered. Thus, 'one-off records in well-watched areas such as Norfolk are much less likely to be under-recorded winter residents than are such reports in, say, Scotland.

Spring passage Records of Great Grey Shrikes in spring, from March onwards, comprise a mix of coastal spring migrants and individuals which could also be considered to be winter wanderers. Their geographical distribution is shown in fig. 5. The existence of a spring migration can be seen from the pattern of records from the Northern Isles (fig. 6). This is further supported by the distribution of spring records, which are concentrated on the English northeast coast and the Scottish southeast coast, as well as in the Northern Isles (fig. 5). Spring passage is not marked, however, with a mean annual total of only 13 individuals. May records are unusual, but include that of a Great Grey Shrike which stayed from 18th May until 8fh July 1991 in Carlton Colville, east Suffolk. There were two June records, both in 1986: at Bellingham, south Northumberland, on 10th, and at Whitby, northeast Yorkshire, on 14th.

Fig. 6. Spring migration of Great Grey Shrikes Lanius excubitor in Northern Isles, Scotland, 1986-92. The period covered, in seven-day periods, is week 10 to week 26 (records from week 14 to week 21), with peak during 16th-22nd April.

Conclusions From the published data, it is possible to give an absolute minimum figure for the number of Great Grey Shrikes visiting Britain; and, using arrival and departure dates, the number present at any one time can be calculated. Fig. 7 shows the average number of Great Grey Shrikes present in Britain in each week during the period 1986-92. There is no hard evidence that there are ever more than about 15 Great Grey Shrikes in Britain at any one time. We would assume, however, that this indicates how difficult the species is to record. More realistically, we would suggest the following figures: Migrants An average of about 40 individuals recorded in autumn and 15 in spring. 484 Fraser & Ryan: Great Grey Shrikes in Britain and Ireland

Fig. 7. Mean number of Great Grey Shrikes Lanius excubitor present in Britain each week, 1986-92.

Winter visitors Around 35 individuals regularly hold territories each winter. In addition, an average total of 40 shrikes is recorded for short periods of time at various locations. The exact status of the latter individuals is impossible to determine. In Scotland, it seems likely that the species is under-recorded, while in England and Wales some duplication may occur if shrikes are roving over large distances during the winter. Currently, a figure of 75 seems to be an upper maximum for the number of Great Grey Shrikes recorded in winter.

Acknowledgments We should like to express our gratitude to the network of observers, county bird recorders, report editors and bird clubs whose records made this paper possible. We should especially like to thank David A. Christie for his invaluable comments and his input to the drafts of this paper.

Summary A total of 890 accepted records of Great Grey Shrikes Lanius excubitor in Britain and Ireland was published in the county, regional and national bird reports for the years 1986-92. Analysis shows that, on average, about 52 were reported on autumn passage, mostly on the East Coast, about 63 overwintered, mostly in southern and eastern England, of which some 37 occupied territories and about 26 wandered more widely, and about 13 were reported on spring passage, mostly on the East Coast. In the Northern Isles, passage reached its peaks in late October and mid April. Taking account of duplication (especially in eastern England) and under-recording (especially in Scotland), it is conjectured that about 40 migrants usually occur in autumn and about 15 in spring, and that a maximum of about 75 individuals overwinters, 35 in large but static territories and about 40 more mobile and roving (or elusive) individuals.

References BANNERMAN, D. A. 1953. The Birds of the British Isles. Edinburgh & London. BRITISH ORNITHOLOGISTS' UNION (BOU). 1971. The Status of Birds in Britain and Ireland. Oxford. CLARK, J. M., & EYRE, J. A. (eds.) 1993. Birds of Hampshire. Hampshire Orn. Soc. CRAMP, S., & PERRINS, C. M. (eds.) 1993. The Birds of the Western Palearctic. vol. 7. Oxford. HUTCHINSON, C. 1989. Birds in Ireland. Calton. LACK, P. 1986. The Atlas of Wintering Birds in Britain and Ireland. Calton. THOM, V. 1986. Birds in Scotland. Calton.

Peter A. Fraser, 12 Redland Court Road, Bristol BS6 7EQ Dr John F. Ryan, Lynwood, Landeryon Gardens, Penzance, Cornwall TR18 4JN