The Influx of Redpolls Into Western Europe, 1995/96 R
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Mike Klangman Mike The influx of redpolls into Western Europe, 1995/96 R. Riddington, S. C.Votier and J. Steele ABSTRACT Winter 1995/96 saw a huge influx of Common Redpolls Carduelis flammea and Arctic Redpolls C. hornemanni into Britain and Western Europe. Two forms of redpoll were involved, the nominate race of Common Redpoll C. f. flammea (‘Mealy Redpoll’) and the Eurasian race of Arctic Redpoll C. h. exilipes, and there is no evidence of any arrivals from other than northern Eurasian populations. Three main influxes were recorded in the north and east of Britain. The first two, in early and mid November, were immediately preceded by or coincided with substantial movements through Utsira in southwest Norway, Heligoland off the northwest coast of Germany, and Falsterbo in southern Sweden; the last of the three arrivals occurred in early December and was associated with the onset of very cold weather, but not with large movements farther north and east. On the British east coast, numbers were the largest since 1975. Heading drawing. Two Arctic Redpolls and one Common Redpoll. © British Birds 93: 59-67, February 2000 59 Riddington et al.: Influx of redpolls in 1995/96 The irruption was absorbed in Britain, and no significant movements were recorded through bird observatories on southern and western coasts. Return spring migration was heavy through southern North Sea sites (which experienced little of the autumn arrival), but was much less apparent farther north. wo species of redpoll occur in in Western Europe. A combination of the Western Europe (fig. 1). Common factors described above forced birds to move TRedpoll Carduelis flammea is a west and south from their breeding grounds familiar breeding bird and/or winter visitor in Norway, north and central Sweden, throughout much of the region, while Arctic Finland and northern Russia. Redpolls were Redpoll C. hornemanni is a rare visitor, recorded in large numbers throughout many mostly in autumn and winter, from breeding parts of Western Europe, with unusually high grounds on the northern tundras of North numbers of both Mealy and Arctic Redpolls America, Europe and Asia. Within both in many areas. Similar invasions have taken species, there are a number of recognisable place in previous winters (notably 1984/85 subspecies (Knox 1988; Svensson 1992), and 1990/91), but, while these pronounced some of which are migratory while others influxes have received a great deal of atten- are predominantly sedentary (Clement et al. tion from birdwatchers, they have been 1993). For example, both the nominate race rather poorly documented. This short paper of Common Redpoll C. f. flammea (widely aims to describe the scale, timing and sub- referred to as ‘Mealy Redpoll’), which breeds species composition of the 1995/96 influx, from Scandinavia (except the south) and with particular reference to Britain and Finland eastwards across north Asia, and Ireland. across much of northern North America, and the Eurasian form exilipes of Arctic Redpoll Methods migrate each year in varying numbers to There are several problems associated with wintering areas south of their breeding documenting invasions of common species. grounds. Conversely, Common Redpolls of Large numbers of observations, from many the races cabaret and islandica (known different sites and observers, are difficult to respectively as ‘Lesser Redpoll’and ‘Icelandic collate and put into context. Indeed, such a Redpoll’) are typically much more sedentary: blanket approach often tells us more about the former breeds from Britain and Ireland, patterns of observer coverage than about southern Norway and southwest Sweden ecological processes. Added to this, the south to the Alps,while islandica is confined highly variable appearance and somewhat to Iceland. confusing taxonomy of the ‘redpoll complex’ In northern breeding areas, food make the task even harder. Acknowledging resources often vary markedly from year to these difficulties, we attempted to devise a year.As a consequence, summers when pop- methodology to minimise such biases. For ulation levels are high (a result of good Common Redpolls, therefore, we used data breeding success following a winter of abun- only from those sites where observer cov- dant seed availability) tend to be succeeded erage was systematic during the 1995/96 by an autumn of widespread seed failure. winter, and also during the preceding and When this happens, unusually large south- subsequent winters. Daily log counts from ward migrations occur which may be termed bird observatories in Britain and Western ‘eruptions’. Later in the autumn, severe Europe were chosen for this purpose. weather may compound these pressures and Although not free from many of the biases act as an additional stimulus for southward that affect observational fieldwork, bird movement. In such years, populations which observatories are typically sited in important are normally sedentary may become migra- coastal migration areas, and are covered on tory,too. most days, in a similar way, by the same, In the autumn and winter of 1995/96, an experienced observers. These factors mean unprecedented arrival of redpolls occurred that, for comparative analysis both within 60 British Birds 93: 59-67, February 2000 Riddington et al.: Influx of redpolls in 1995/96 Fig. 1. Breeding ranges in Europe of Common Carduelis flammea and Arctic Redpolls C. hornemanni. Nos. 1-16 indicate location of bird observatories which provided data on Common Redpolls: 1 Fair Isle; 2 North Ronaldsay; 3 Copeland; 4 Cape Clear; 5 Calf of Man; 6 South Walney; 7 Bardsey; 8 Portland; 9 Spurn; 10 Gibraltar Point; 11 Sheringham; 12 Sandwich Bay; 13 Dungeness; 14 Utsira; 15 Heligoland; 16 Falsterbo. and between seasons, our data are as accu- tively). Thirteen British and Irish observato- rate and reliable as possible without a pre- ries responded to our request for data, as did determined methodology. In essence, we three foreign stations, making 16 study sites have sacrificed greater geographical cov- in total (fig. 1). erage in favour of more systematic and rig- In addition, all records of Arctic Redpolls orous data from a smaller number of sites. accepted by the British Birds Rarities Com- All bird observatories in Britain and mittee (BBRC) for the winter 1995/96 (see Ireland, together with four others in Western Rogers et al. 1996-1999) were analysed. Europe, were sent a series of simple forms Although these data are not derived in the on which to record Arctic and Common same systematic manner as those for Redpoll sightings on a daily basis from Sep- Common Redpolls, they nevertheless tember 1995 to May 1996. Recorders were provide an instructive insight into the distri- asked to differentiate recognisable sub- bution of this tricky species (see Votier et al. species of redpoll where possible, and also 2000). to distinguish between those days when Results there was observer coverage of the site but To investigate the magnitude and timing of no redpolls were seen and those when no the arrival in 1995/96, and to compare it observers were present. Finally, they were with the winters immediately before and asked to provide a monthly summary of after, we analysed data from six sites in redpoll counts in the previous and subse- detail.These encompassed two from the east quent winters (1994/95 and 1996/97, respec- coast of Scotland (Fair Isle, Shetland, and British Birds 93: 59-67, February 2000 61 Riddington et al.: Influx of redpolls in 1995/96 Fig. 2i. Monthly mean daily counts of Common Redpolls,Fig. 2ii.Utsira. Monthly mean daily counts of Common Redpolls, Fair Isle. 200 2i. Utsira, south 20 2ii. Fair Isle, Norway Shetland 150 15 100 10 50 5 0 0 S O N D J F MAM - S O N D J F MAM - S O N D J F MAM S O N D J F MAM - S O N D J F MAM - S O N D J F MAM Fig. 2iii. Monthly mean1994/95 daily counts 1995/96 of Common 1996/97 Redpolls, Fig.North 2iv. Ronaldsay. Monthly1994/95 mean daily counts1995/96 of Common 1996/97 Redpolls, Spurn. 20 2iii. North 40 2iv. Spurn, East Ronaldsay, Yorkshire Orkney 15 30 10 20 5 10 0 0 S O N D J F MAM - S O N D J F MAM - S O N D J F MAM S O N D J F MAM - S O N D J F MAM - S O N D J F MAM Fig. 2v. Monthly mean1994/95 daily counts 1995/96 of Common 1996/97 Redpolls,Fig. Sheringham. 2vi. Monthly mean1994/95 daily counts 1995/96 of Common 1996/97 Redpolls, Heligoland. 50 2v. Sheringham, 80 2vi. Heligoland, Norfolk off northwest 40 Germany 60 30 40 20 20 10 0 0 S O N D J F MAM - S O N D J F MAM - S O N D J F MAM S O N D J F M A M 1994/95 1995/96 1996/97 1995/96 Fig. 2. Mean daily counts of Common Redpolls Carduelis flammea at six sites in Western Europe for each month September-May in the three winters 1994/95-1996/97. For Heligoland (2vi), data are available only for 1995/96. North Ronaldsay, Orkney), two from the east To analyse magnitude and timing of the coast of England (Spurn, East Yorkshire, and influx, counts of all Common Redpoll sub- Sheringham, Norfolk), one from the west species were pooled. At most sites, the coast of Norway (Utsira) and one from the majority of individuals were not assigned to northwest coast of Germany (Heligoland). subspecies with complete confidence.This is All of these sites are in areas where the quite understandable given the difficulties of redpoll invasion was pronounced. Summary identification if views are brief, as, for data are provided for remaining sites, which example, at Falsterbo in south Sweden and at either are in areas that were largely unaf- Sheringham, where a large proportion of the fected by the influx or did not have suffi- records are of birds passing over on active cient observer coverage to permit more migration.