Spring weather and the migration of geese from Scotland to Iceland

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1 Ringing & Migration ISSN: (Print) (Online) Journal homepage: Spring weather and the migration of geese from Scotland to Iceland Hugh Boyd, Michael V. Bell & A. Donald Watson To cite this article: Hugh Boyd, Michael V. Bell & A. Donald Watson (2000) Spring weather and the migration of geese from Scotland to Iceland, Ringing & Migration, 20:2, 3, DOI: / To link to this article: Published online: 11 Apr Submit your article to this journal Article views: 329 View related articles Citing articles: 5 View citing articles Full Terms & Conditions of access and use can be found at Download by: [ ] Date: 01 January 2018, At: 12:48

2 Ringing & Migration (2000), 20, 3 Spring weather and the migration of geese from Scotland to Iceland HUGH BOYD 1*, MICHAEL V. BELL 2 and A.DONALD WATSON 3, 1 Canadian Wildlife Service, Environment Canada, Ottawa, Canada K1A 0H3, 2 48 Newton Crescent, Dunblane, Perthshire FK 0DZ, UK, 3 54 Main Street, St John's Town of Dairy DG7 3UW, UK Downloaded by [ ] at 12:48 01 January 2018 Records of first arrivals of geese at sites in Iceland between 1950 and 1997 are combined with dates of departures from Scottish roosts and flights seen over northern Scotland to identify when migratory movements occurred. Greylag Geese Anser anser moved earliest, the mean date of first sightings in Iceland being 3 April (s.d.14.3 days) and of northward movements over Scotland 14 April (s.d days), the median first arrival and departure dates being 8 and April. The mean date of first sightings in Iceland of pinkfooted geese Anser brachyrhynchus was 13 April (median 21 April) and of Scottish departures 20 April (median 25 April). The mean dates of Scottish departures and Icelandic sightings of Greenland Whitefronted Anser albifrons flavirostris, Barnacle Branta leucopsis and Brent geese Branta bernicla all lay between 18 and 22 April, with median dates from 19 to 27 April. Arrivals in Iceland were associated with anticyclonic conditions over Scotland on the previous day, while cyclonic conditions were avoided. There were more sightings over Scotland when conditions were unfavourable than would be expected from the frequencies of those conditions in April. There were unexpectedly few movements around dates of full moons (+/ 2 days). The three grey geese, but not the black geese, have tended to arrive in Iceland earlier in recent years. Head and westerly winds were far more frequent than tail winds, especially after 1970, and there is some evidence of eastward drifting, yet the energetic demands of the flight from Scotland to Iceland can rarely have been severe. Williamson (198) described the weather be close similarities in the timing of movements conditions under which geese were likely of four of the five species of geese from the British to be seen migrating over northwest Scotland to Isles to Iceland. Iceland in spring. Fox et al (1989) showed that The Barnacle Geese Brantą leucopsis that stage variations in the breeding success of Greylag in Iceland breed in east Greenland. Greenland Anser anser and Pinkfooted geese Whitefronted A.albifrons flavirostris and Brent A.brachyrhynchus nesting in Iceland were geese B.bernicla hrota also move through Iceland correlated with meteorological variables in without breeding. The former breed on the midspring, including conditions in Scotland before western lowlands of Greenland. Brent Geese they migrated and in Iceland between arrival make another long flight to the eastern Queen and nesting. By design, the work reported here Elizabeth Islands, in northeast Canada. Thus, used less detailed weather information than while the Greylag and most of the Pinkfooted those earlier studies, in an attempt to see geese have completed their spring migration by whether summary data, readily available reaching Iceland, the other geese have further historically and suitable for comparing with long journeys to make. These different demands scenarios of possible future climatic changes, seem likely to affect the physiological yielded results comparable with those based on preparations of individuals of each species for more detailed weather records. There prove to the journey from Scotland to Iceland, in addition * Corrrespondence author to their lengths of stay in Iceland British Trust for Ornithology

3 4 Hugh Boy d et al. MATERIALS AND METHODS Icelandic goose records The dates of first arrivals of migrant birds, including geese, at some weather stations in Iceland have been published for many years in the May issues of Vedrattan (the journal of record of Vedurstofa Islands, the Icelandic Weather Office). They are limited to a single annual date for each species, and there have been very few notes of Brent or Whitefronted geese. Few weather observers have been reporting bird sightings in recent years (Trausti Jonsson, pers comm). The Icelandic Institute of Natural History holds an unpublished collection of first sightings of migrant species in spring, assembled by the late Finnur Gudmundsson from records supplied by correspondents in many parts of the country. These notes often include records from several sites in the same year, giving some indication of local variations in arrival dates. Most of the goose records were made between 1932 and 1970 and refer to Greylag Geese: only records after 1950 are used here. The reporting stations were well scattered. Spring migration by geese is usually protracted, so that first sightings in Iceland record only the beginning of immigration. Scottish goose records Most of the Scottish data used here consist of unpublished notes on departures from three major inland roosts: (1) by M.V.Bell at Carsebreck, Perthshire (5 1'N, 3 51'W) of Greylag and Pinkfooted geese in ; (2) records of Pinkfooted Geese at Fala Moor, Midlothian (55 49'N, 2 55'W) made by the late William Brotherston, ; and (3) departures of Greenland Whitefronted Geese from Loch Ken, Galloway (54 5'N, 3 58'W) noted by A.D.Watson from These records have been supplemented by published notes on geese leaving or on migration, taken from Scottish Bird Reports and regional journals. Departures from Carsebreck and Fala were usually seen in the evening, although departures of Whitefronted Geese from Loch Ken were noted at all times of day. If most journeys to Iceland are made at night, that could account for the greater scarcity in spring than in autumn of sight records of geese moving across Scotland. Some of the published records from coastal sites note that goose movements took place over 5 days, or even longer, with especially large numbers on only one or two days. Until very recently, late sightings in Scotland usually referred to very small numbers of geese, unlikely to be of importance to the population. Records later than May have been omitted from the analyses, though in some recent years several hundred Pinkfooted Geese have remained at Carsebreck and in Lancashire (A.D.Fox, pers comm) well past that date. Most of the Scottish records are of Pinkfooted Geese and refer to years after There are few years with several records of a single species from both countries. Weather records from the British Isles Lamb's (1972) catalogue of the dominant atmospheric circulation system over the British Isles on each day since 181, updated in Hulme and Barrow (1997), provides a concise summary of great amounts of information. Lamb used the 'square' 50 to 0 N and 10 W to 2 E to represent the British region; i.e. he included the sea area around the British Isles. He also took account of upper airflow patterns. He identified eight directional components (NE, E, SE, S, SW, W, NW and N) and two vorticity components (A, anticyclonicity and C, cyclonicity) with 'hybrids' producing twentysix alternatives in all, less than 4% of days being unclassifiable (U). In using the records for MarchMay here, the seven main types were retained, with the 'hybrids' lumped into three classes: A+ (those including anticyclonic features, C+ (with cyclonic features) and O (all others, including U). Further aggregations were used to avoid too many very small samples: 1) the systems labelled N, NW and NE were grouped as N+, involving head winds likely to make migration more difficult or dangerous; 2) the systems S, SE and SW were grouped as S+, involving tail winds, presumably helpful to migrants. Though SW winds might tend to carry birds to the east of Iceland, they formed one of the least frequent classes in April in the sample years, so that any misallocation of SW systems is unlikely to have had important effects on the analyses British Trust for Ornithology, Ringing & Migration, 20, 3

4 Recognizing that conditions over different regions within the British Isles often differ from each other and from the overall assessment, Mayes (1991) developed separate daily and monthly indices for Scotland, Ireland, the Southwest (southwest England and South Wales) and the Southeast (of England), from 1950 onwards. These, like the British Isles series, are being updated continuously (J.Mayes, pers comm). Mayes concentrated on surface airflows over land, his special interest being in rainfall patterns. Because of its widespread acceptance, Mayes retained the categories and nomenclature of Lamb's classification system. The differences in the data considered by Lamb and by Mayes result at times in marked differences between their daily classifications, which affect their matching against local conditions in the Outer Hebrides and comparisons with observed goose movements. The other British meteorological data used were records of monthly mean temperatures and precipitation at Blackford Hill, Edinburgh (55 55'N, 3 O 11'W), representing the Scottish wintering ranges of the grey geese. Blackford has a long run of weather records, as does Stornoway (58 02'N, 19'W), in a region overflown, and sometimes stopped in, by many of the migrating geese. Though Stornoway is warmer than Blackford, the statistical relationships between goose movement data and monthly means of temperature and precipitation at the two stations do not differ importantly. Data from Stornoway were used here only in dealing with Williamson's (198) observations. Weather records from Iceland The principal meteorological data from Iceland used were daily and monthly mean and minimum temperatures and total precipitation at Stykkisholmur (5 05'N, 22 44'W), where records have been kept since 184, together with those from three stations in southern and eastern areas used, or passed over, by geese in spring: Holar i Hornafirdi (4 18'N, 12'W), Kirkjubaejarklaustur (3 47'N, 18 04'W) and Teigarhorn (4 41'N, 14 21'W). Monthly summaries of wind directions and speeds at those three stations and daily records of hours of bright sunshine at Holar provided additional Goose migration from Scotland to Iceland 5 indicators of conditions in the southeast. Stykkisholmur, on the west coast, is near the centre of the spring distribution of Brent Geese, about 70km NNW of the principal area used by Whitefronted Geese and 100km WSW of the main spring staging area of Barnacle Geese. Most Pinkfooted Geese occur km to the SE. While Greylag Geese are widely scattered through the lowlands, their nesting density is high in Myrar, 5070km south of Stykkisholmur. The long run of weather records from Stykkisholmur has been used effectively by agronomists to represent conditions across the whole of Iceland in studying the effects of climate on the growth of grasses in spring (eg Bergthorsson 1985). Daily and monthly temperatures at stations in the main spring staging areas of grey geese were highly correlated with those at Stykkisholmur and with each other. Though daily measurements of winds and cloud cover over Iceland are not published, daily summaries of the numbers of stations recording strong winds and fog were of some help, in conjunction with the published records of daily temperatures and precipitation at the stations in the southeast, where the majority of the geese might be expected to make their landfalls. RESULTS GOOSE MOVEMENTS Arrivals in Iceland Geese, flying at 400km/hr (Ogilvie 1978), might take 22 hours to fly from the north of Scotland to southeast Iceland (800l,000km) in still air, less with following winds. Though geese are unlikely to leave Scotland against strong head winds, they may meet them before completing the flight, when the effort needed to reach Iceland could be increased substantially. If flights usually begin in the evening, the geese should reach Iceland during the following morning. Thus the difference between the dates of departure and arrival of any group should be small. Though about 80 weather stations were operating in the 1950s and 130 in the 1990s, there have been records of arriving geese from only 21, nine of them well inland. At nearly all the coastal stations the prevailing winds were off 2000 British Trust for Ornithology, Ringing & Migration, 20, 3

5 Hugh Boyd et al. the sea (S or SE in southeast Iceland, NE in the northeast and SW in the southwest). At inland stations, most prevailing winds were from the SW. The records in the Icelandic Institute of Natural History add another 38 localities where geese were seen, for totals of 2 coastal and 33 inland sites. In Table 1, the country is divided arbitrarily into quadrants by the lines of latitude 5 N and longitude 18 W. Though geese were not often noted at most of the sites, there were long runs of records from several, most notably Kvisker (3 59'N, 1 2'W), where natural history observations have made for more than sixty years (Bjornsson 197). At Kvisker nearly all the geese seen in spring are flying west. Though it might be expected that most new arrivals in Iceland would be seen on the south coast, this was not the case. Many first sightings were in the northeast (Table 2), even after allowing for the greater number of reporting stations there; and many were well inland where, again unexpectedly, they tended to be slightly earlier than on the coast. Though grass growth begins earlier on the coastal lowlands than in the interior, early arrivals inland imply that the geese aimed for familiar places, probably with less human disturbance than on the improved grasslands near the coast. The mean date of first arrival of Greylag Geese in Iceland was 3 April, the median 8 April (Table 3). For Pinkfooted Geese the mean date of first sightings was 13 April, the median 21 April. Until the last 20 years, most of the Pinkfooted Geese breeding in Iceland (more than 80% of the entire stock) did not settle in the lowlands, where the Greylag Geese breed, but moved directly into the thinlypeopled uplands, close to their eventual nesting places in the central highlands (Finnur Gudmundsson, pers comm). Though the great increase in the population over the last fifty years has led to increasing numbers of Pinkfooted Geese nesting at lower altitudes, there have been few recent reports of first sightings, presumably due to loss of interest in reporting. The mean dates of first sightings in Iceland were 21 April for Whitefronted, 18 April for Barnacle and 21 April for Brent geese (Table 3), the corresponding median dates 21, 23 and 27 April. Departures from Scotland Table 3 summarizes both the recorded arrivals in Iceland and departures from Scotland in spring. As the majority of the Icelandic records are of 'first first' sightings, while the Scottish records tend to emphasize late departures, combining the records probably gives the best available pictures of the peak(s) and span of the migration of each species. Though no March departures of identified Greylag Geese were found in the sources searched, the 'grey geese' leaving Scotland in March have been tabulated as this species. The mean date of reported movements of Greylag Geese over Scotland was 14 April (n = 83, s.d. 12.9), the median April. The latest record of apparent migration was on 1 May, but there were few Scottish records after 25 April. Thirtyeight of 372 movements of Pinkfooted Geese in Scotland reported between 1951 and 1995 were in March, 33 of them in Nearly all those seen before 25 March (the earliest arrival date noted in Iceland) were probably movements within Britain, rather than Table 1. Number of sites in Iceland from which records of goose arrivals were reported in any spring, Weather = weather station; Watchers = other observers. Region Weather Watchers Total Coastal Inland NW NE SE SW Iceland British Trust for Ornithology, Ringing & Migration, 20, 3

6 Goose migration from Scotland to Iceland 7 Table 2. Numbers of first sightings of geese in different regions of Iceland and at coastal and inland sites. Region Greylag Whitefront Pinkfoot Barnacle Brent fofa/ NW NE SE SW total coastal inland _ as percentage of occurrences of each species Downloaded by [ ] at 12:48 01 January 2018 NW NE SE SW coastal inland Table 3. Mean dates of observed departures of five species of geese from Scotland in spring and of their first arrivals in Iceland, ; and periods of most movements. Decadal means are for combined Scottish and Icelandic records; not shown for Greylag, , because transcription of Scottish records incomplete, or for Brent, samples too small, n = sample size, sd = standard deviation. dep.scotland n sd 1st Iceland n sd Greylag April April Pinkfoot April April Whitefront April April 21.0 Barnacle April April Brent April April most movements (April) May decadal means (all April) r(years) P < < NS 0.29 NS 2000 British Trust for Ornithology, Ringing & Migration, 20, 3

7 8 Hugh Boyd et al. emigration. Fox et al (1995) showed that a gradual northward shift from England to Scotland begins as early as February. In recent years most Pinkfooted Geese have accumulated in northeast Scotland (Bell et al 1988, Bell & Newton 1995) before migrating. If the records before 25 March, and twelve later than May, are excluded, the mean date of Scottish movements is 20 April (s.d. 11.0). In , sightings of Pinkfooted Geese in May were proportionately fewer (44/4 = 28.%) than they had been in earlier years (37/82 = 45.1%), while there were more sightings in March. Reported movements of Greenland Whitefronted Geese were more concentrated than those of other species, 27% from 120 April and nearly 22% from 2125th. There has been a statistically significant shift towards earlier departures from southwest Scotland in the 45 years since 1952, but this has been obscured by late sightings elsewhere. The total span of movements has not changed, but the mode shifted from 2125 April in to 11 April in There were 30 Scottish records of migrating Barnacle Geese and 32 of arrival in Iceland (records of Barnacle and Brent geese from Fair Isle and Shetland were excluded, because they could be of birds on their way to Spitsbergen, not Iceland). They show similar mean dates of movement. The timing of their movements has not become earlier: in (n = 2) the mean date of movement was 13 April; since 1980 (n = 3) it has been 22 April. The difference is not statistically significant, the scatter of dates being wide. There were only records of migrating Brent Geese from Scotland and 17 from Iceland, spread from early April to midmay, with the means and medians at the end of April. There are too few records to show significant changes in the timing of movements. Departures and arrivals Only for the Greylag Goose are there substantial differences in the mean and median dates of record in the two countries (Table 3). Yet there are no statistically significant associations between the reported dates of arrival in Iceland and departures from Scotland in any year, presumably due largely to the incompleteness of the records. Pinkfooted Geese were quite often seen flying over Scotland on the dates when they were first sighted in Iceland, but the scarcity of sightings in Iceland prevents detailed comparisons. WEATHER AND GOOSE MOVEMENTS Scottish seasonal weather and arrival dates The mean winter temperatures and total precipitation in winter (here, following Icelandic practice, the five months NDJFM) and in April at Stykkisholmur and at Blackford do not track each other closely. Except on the infrequent occasions when snow cover persists for more than a week in those lowland areas of Britain that most geese use, direct effects of winter precipitation on the geese are probably slight. There were too few Icelandic sightings after 1980 to estimate recent peak arrival dates. During the period there were no significant correlations between the arrival dates of Greylag Geese and mean winter temperatures in Scotland or Iceland, except in , the secondcoolest decade of the century (Hulme & Barrow 1997), when arrivals were later after cooler winters at Blackford (n = 10, r = 0.25, P < 0.05). Arrival dates of Greylag Geese tended to be earlier in years when spring (MarchApril) at Blackford was relatively warm (n = 49, r = 0.330, P < 0.02). Over the entire period, there was no consistent relationship between first sightings in Iceland and Blackford spring temperatures. During most of the period , there was no simple statistical relationship between the timing of Greylag Goose arrivals in Iceland and total winter precipitation at Blackford. However, when the trend towards earlier arrival is partialled out, a strong relationship is seen for the entire period (n = 45, r(ga.ewr.), P = 0.373, P < 0.01), i.e. wet Scottish winters were followed by earlier arrivals. There are too few recorded arrivals of other geese to permit similar analyses. Though the longterm means of daily temperature in Iceland show a steady daily increase through April and May, there is much detailed variation between years and there is usually at least one cold spell in late April or early May. These cold spells have immediate effects on the condition of the geese already in Iceland (Boyd & Fox 1995), but no detected effect on times of arrival British Trust for Ornithology, Ringing & Migration, 20, 3

8 Departures from the Outer Hebrides Williamson's account (198) of observations on Lewis and Harris and on St Kilda included notes on geese which set off northwest but returned when they encountered poor visibility or headwinds. Some returned almost immediately, others straggled back several hours later. He related these returns to conditions indicated on the daily weather maps. This helped the recognition of the role of persistent and slowmoving anticyclones in encouraging northward movements in spring (Elkins 1983). Williamson recorded the local sea level atmospheric pressure on 3 observation days in 1957, 1959 and 190. There was a positive correlation between the numbers of geese seen migrating and the local pressure (n = 3, r = 0.375, P < 0.05), with northward movements seen on only one day when the pressure was low (991mb) and most when it exceeded 1,017mb. Migrating geese cannot take advantage of favourable wind conditions occurring after they have made their journey. If feeding and weather conditions in the first half of April, or the advanced sexual development of the geese themselves, have encouraged early departures, anticyclonic conditions over Scotland in late April and early May may be "wasted". Most departures from Lewis (4/5 = 70.8%) were seen when the airflow over Scotland was anticyclonic, yet no movements were seen there on 32/82 (39%) of anticyclonic days in April and early May. Prior departures could account for the high proportion of anticyclonic days with no recorded emigration, both in the period covered by Williamson's study and in more recent years. It also seems possible that on some anticyclonic days migrating geese were flying too high to be detected. Movements and winds over the northeast Atlantic The centre of action of the Azores High shifts north in spring shifts north from about 31 N in March to about 33 N in May, so that southerly wind, infrequent early in April, occur much more often in the last ten days (Santer 1988). The mean wind strength also decreases, which should also improve conditions for migration. In nearly all years since 1950, conditions for migration in April have been far more often Goose migration from Scotland to Iceland 9 unfavourable than favourable. The mean monthly frequency of anticyclonic (A) days was only 4.9 (s.d. 4.3) for Scotland, where they have tended to become fewer (r = 0.21, 0.1 > P > 0.05), especially in the second half of the month (mean 3.0, s.d. 2.8, r^ 0.38, P < 0.02), though continuing to be more frequent than in the first half in most years. In southeast Iceland the frequency of head winds was high and variable in the 1950s (mean 38.4 %, s.d. 19.0), less, and much less variable, in the 190s (mean 33.7%, s.d. 7.), and has since increased (1970s 37.9%, s.d. 14.3; 1980s 43.7%, s.d. 14.4, %, s.d 12.8). Following winds (mean 12.9 %, s.d..0) and cross winds (mean 29.2%, s.d.10.3) were scarcer, and showed no trends over the years. April 1974 was quite exceptional, with 21 anticyclonic days over Scotland (the next highest total being 14 in 1954). Over southeast Iceland there were tail winds 29% of the time and only.3% of head winds. The first emigrant Greylags were noted on 2 April (only matched in 1982), with the first arrival in Iceland on th. No arrivals of Pinkfooted Geese were reported in 1974, but the first emigrants were seen over Scotland on 14th, nearly a week earlier than the mean, though there were earlier records in many other years. Whitefronted Geese were also about a week early, seen leaving Scotland on 13th and arriving in Iceland on th. Yet recorded movements of Barnacle and Brent geese were not unusually early in In the four other years with > 20% of tail winds in April (1952,1955,1984,1987) sightings were scarce, especially in Iceland, and did not suggest abnormally early migration of any species. There were only two other years with < 20% head winds (1955, 19): in 19 both Greylag (30 March and Pinkfooted (5 April) geese were seen to arrive early in Iceland, but there were no records of early departures from Scotland. In the three years with > 0% head winds in April (1953, 198, 1994), which might have been expected to delay migrants, Pinkfooted Geese were seen leaving as early as 13, 8 and 10 April respectively, while Greylag Geese had arrived on 2 April in 1994, though not until 14th in The timing of Barnacle Goose movements did not seem to be affected by the proportions of head or tailwinds British Trust for Ornithology, Ringing & Migration, 20, 3

9 10 Hugh Boyd et al. Downloaded by [ ] at 12:48 01 January 2018 Given that the journey to Iceland is likely to 9/1 occasions there were favourable systems take less than 20 hours, the predominance of over Scotland on that day, with only 5 or on unfavourable winds need not present a serious the preceding five days. Thus there is some obstacle, though it might be expected to lead to evidence from the general records that geese accumulations of geese waiting for a break in wait for favourable conditions, but it is not as the weather. The IINH records rarely say strong as that provided by the direct anything about the numbers of geese arriving, observations in the Outer Hebrides (Williamson and the published weather station records never 198). do. The Scottish records sometimes note large On the assumption that most flights took place movements, but not in a consistent way. With overnight, dates of first sighting in Iceland were the material available, the only way to test the compared with the atmospheric circulation over hypothesis that geese wait for favourable Scotland on the previous day. (The Scottish and weather is by looking for clumps of records of British circulation types on the day of arrival and several species migrating on a single day. There two days previously were also looked at: the were 28 occasions when clumps were noticeable, results are not reported, as they do not alter the mostly between and 20 April, at the start of general picture.) the peak period of migration. Conditions for Thirteen of 132 records of Greylag Goose migration were favourable (with A, A+ or S arrivals in were from dates in March, systems over Scotland) on the day of movement 9 between 1 April and 22 in 130 April, with on 13/28 days; 11/28 of the immediately only one in May. Almost all the arrivals in the preceding days had favourable systems, with 12, second half of April were noted before 190. This 10,8 and 9 two, three, four and five days earlier. seems not to have been due to atmospheric Looking only at the first day of each clump, on conditions in the first half of April having been Table 4. Relationship of goose movements and weather conditions over NW Scotland on observation days between 11 April and 10 May in (from Williamson 198) to atmospheric circulation types on the same day over the British Isles (Lamb 1974) and over Scotland (Mayes 1991). circulation types (1) days with geese moving north frequency of systems British Isles Scotland A,A C,C+ 9 other 17 total (2) no geese seen going north frequency of systems British Isles Scotland total observation days 124 Comparing days with and without goose movements X 2 2: British Isles 14.99, P< 0.001; Scotland 2.99, P> 0.1 It was by chance that the number of days with goose movements was the same as the number when no movements were noted British Trust for Ornithology, Ringing & Migration, 20, 3

10 less favourable in than in recent years. Arrivals of Greylag Geese tended to be more frequently associated with anticyclonic and less with cyclonic systems over Scotland on the previous day than would be expected from the frequencies of occurrence of those systems (Table 5). As Icelandic sightings of the four other species were fewer, and they showed no consistent differences in their Icelandic responses to Scottish weather, they have been treated as a single group. Greylag Geese were more likely than other species to have moved when the winds over Scotland look to have been unhelpful (from west through north to east). The monthly summaries in Vedrattan of mean wind strengths and the percentages of winds from different compass directions during the month are listed separately so that, though it is possible to test their possible influence on goose arrivals separately, they cannot be tested together. Yet it is obviously important to know whether strong winds over southeast Iceland were assisting or hampering arriving geese. Greylag Geese tended to arrive later in years when strong winds were frequent in the period Table 5. Recorded arrivals of geese in Iceland in April compared with weather systems over Scotland on the previous day. 'other'=sums of records of all species other than Greylag. 'frequency'=total number of days with these systems (from Table 5). *= difference between observed and expected frequencies significant at 5 % level. system A A + S+ C c+ NW,N W E U total Greylag 40* 11 3* 14,NE other species 3* * frequency observed frequency expected frequency Greylag other / Goose migration from Scotland to Iceland April. The recorded arrivals of other geese in Iceland are too few to provide reliable pictures of their sensitivity to wind conditions over Iceland on arrival. There were no statistically significant relationships, for either Greylag or Pinkfooted geese, between mean April sealevel pressure over southeast Iceland and the timing and scatter of arrival records. Movements in Scotland Sightings in Scotland in later years confirm Williamson's (198) observations that migratory movements occur under a wide range of circulation systems, though emigration may be less strongly associated with anticyclonic conditions than he concluded. In the years , for which there are most records of Greylag Geese, the frequency distribution of circulation systems over the British Isles on 78 days when movements were reported corresponded quite closely to the April frequencies of the systems themselves, except that few movements were seen on days with systems including cyclonic elements (Table ). The much larger sample (29) of Pinkfooted goose movements in April and 1 May also showed no marked association with anticyclonic conditions, though a relative scarcity of movements when southerly or westerly systems were present. Of 39 movements of Pinkfooted Geese in March, 17 occurred under unfavourable conditions (W, NW, N systems) and only under anticyclonic conditions (numbers expected from total frequency distribution of systems in March 9 and 10 respectively). If, as suggested earlier, most of these March movements were due to repositioning in Scotland, involving no ocean crossings, perhaps the geese did not need to wait for favourable weather. The same tendency for movements to be spread among all types of systems was shown by Whitefronted Geese (n = 145), apart from an apparent avoidance of easterly systems (which have been scarce in recent years). The few Scottish records of Barnacle and Brent geese also suggest no significant preference for, or aversion from, particular circulation systems prevailing over the British Isles on days with movements, nor those on the previous or following days British Trust for Ornithology, Ringing & Migration, 20, 3

11 12 Hugh Boyd et al. Do migrating geese take advantage of full likely to be helpful, though the extent and nature moons? of the cloud cover will have affected its,.,, brightness. (The choice of a 5day period is In wintering areas where they are much J T J J I. J disturbed geese often feed at night, especially arbitrary; 3 and 7day periods were also tried during the period around full moon. There is įf ve ^ ^ Y w e a k results c The also a common belief that geese are most likely numbers of movements of all five species to migrate at that time. Here, 5day periods of S eese durin S t h o s e potentially favourable centred on the dates of full moons occurring periods were compared with those at other times between 25 March and May are taken to (Table 7). For the entire spring period, the null represent the times when moonlight was most hypothesis that there would be no statistical Table. Weather systems over Scotland on days on which departures of geese from Scotland were noted compared with total frequencies of those systems in April: (a) Greylag; (b) Pinkfooted; (c) Whitefronted geese. Numbers of occurrences significantly greater than expected frequencies shown in bold, those fewer than expected shown in italic. Downloaded by [ ] at 12:48 01 January 2018 frequency of system types A A+ S+ C C+ N+ W E U total (a) Greylag (April ) movements 21 total frequency 54 chisquare , P < (b) Pinkfooted (1 Apr May, ) movements total frequency chisquare , P < (c) Whitefronted (April ) movements total frequency chisquare 1.544, P < Table 7. Frequency of: (a) arrival of geese in Iceland at times of full moon (+/ 2 days) and (b) departures from Scotland at different periods of spring migration. Records of all five species combined, Expected frequencies [In italic) derived from numbers of days near full moon and others during period, assuming null hypothesis Mar 335 Apr 130 Apr 1 May total significance (chisquare) (a) arrivals near full moon total (b) departures near full moon total , P > 0.1.1, P > 0.1 (a) + (b) arrivals and departures 8.42, P > British Trust for Ornithology, Ringing & Migration, 20, 3

12 difference in their frequency per 5day period cannot be rejected when the arrivals and departures are considered separately. When both sets of records are combined, the totals observed during full moon periods are slightly less than would be expected by chance, with more than expected in late March but fewer through April and early May. Though the extent of nocturnal cloud cover over the northeast Atlantic must have been recorded routinely by satellites since the late 190s, no summary analysis seems to have been published. Using daily rainfall in southeast Iceland as a proxy for cloud conditions over the sea area between Scotland and Iceland, goose arrivals do not seem to have been related to rainfall amounts, either around the time of full moon or in other potentially darker periods. In several years, arrivals were noted on days when rainfall amounts were the highest for any day in April. DISCUSSION Why do Greylag Geese leave Scotland earlier than the other species? Two reasons seem plausible. Nesting in the Icelandic lowlands, where persistent snow cover usually ends before the end of April, they are able to exploit the 'early bite' in April and begin nesting early in May (Bardarson 198). It is also possible that, being larger than the other geese, they are better able to deal with contrary winds, so do not need to wait for the increased frequency of helpful weather systems in the second half of April. Why do the other four species all leave Scotland and arrive in Iceland at much the same time? If migration were driven chiefly by the stimulating effect of increasing daylength on the endocrine system and gonads, they should gain from moving as soon as possible after the equinox, as daylength increases more rapidly at higher latitudes. Yet they wait for another four weeks. As grass growth begins later in Iceland than in lowland Scotland, this enables them to benefit from the 'early bite' in both countries. Pinkfooted Geese breeding in the central highlands of Iceland can often be seen making short reconnaissance flights up the Thjorsa valley in early May to see whether their breeding places are sufficiently free of snow to be ready to occupy (Boyd, pers. obs.). Goose migration from Scotland to Iceland 13 Whether any of the geese breeding in Greenland make comparable exploratory flights from northwest Iceland is not yet known. The journey to east Greenland (001000km) is perhaps short enough to allow Pinkfooted and Barnacle geese to return to Iceland if their breeding sites are still snowcovered. Snow cover in the coastal lowlands of west Greenland usually begins to clear by the beginning of May (Fox & Ridgill 1985), so that Whitefronted Geese can move on from Iceland early in May without undue risk. The Brent Geese must wait in Iceland until the end of May or early June before they can return to their High Arctic breeding places with a high probability of being able to embark on nesting before the energy reserves they have carried with them have been exhausted. The occurrence of more first sightings of geese in the northeast of Iceland than in the southeast or southwest seems likely to reflect the predominant influence of weather systems travelling from the west across Iceland and the northeast Atlantic Ocean. These systems will tend to carry spring migrants east of their intended landfalls. Whether substantial numbers of geese are ever carried far enough off course to be unable to reach Iceland before becoming exhausted is not known. Fox et al (1989) showed that the breeding success of geese nesting in Iceland was influenced by spring weather in Scotland as well as in Iceland. Additional studies of geese staging in Iceland are needed before it is possible to determine to what extent the demands of the flight from Scotland to Iceland may affect the onward movement of Whitefronted or Barnacle geese, or their subsequent breeding performance. Phenological recording has been out of fashion for many years, except in local journals not intended for a scientific audience. There can be very little 'quality control' in using notes made many years ago by observers no longer available, or records published in local and national journals after severe condensation by editors with limited space to fill. So it is proper to ask whether retrospective studies based on haphazard recording are capable of providing reliable results, while acknowledging that most historical studies involve similar difficulties in making something out of information collected in the past for different purposes. As the sections 2000 British Trust for Ornithology, Ringing & Migration, 20, 3

13 14 Hugh Boyd et al. based on incidental observations in Scotland have shown, the signals are accompanied by a great deal of noise, while first annual records in Iceland may not be a reliable guide to the timing of following waves of returning migrants. What has emerged is a crude set of snapshots of largescale movements never seen as a whole in any single spring. Yet the results, though imprecise and very incomplete, are not chaotic. There are persistent patterns, extending across all the species looked at, that seem sufficiently consistent to permit their use in considering changes in migratory behaviour over time, outside as well as within the period in which the observations were made. Do the results make it possible to frame useful questions that could be answered reliably, affordably and fairly quickly by systematic observational studies in the future? There are obvious practical difficulties in assembling teams of observers simultaneously in two countries and holding them together through several successive springs. This would almost certainly have been easier to do in the 1950s than now, when many birdwatchers have more money and it is much easier for them to travel to distant countries. More fundamentally, this study seems to show that simply intensifying observations of departures from Scotland and arrivals in Iceland is unlikely to add much to knowledge. The flight from Scotland to Iceland is apparently not a severe enough physiological test of the capabilities of migrating geese to yield new insights into their performance. ACKNOWLEDGEMENTS Typescripts of field notes made by the late William Brotherston at Fala Moor provided the initial stimulus for this study. We are indebted to Mrs Helena Brotherston for permitting HB to use those records; and to the Scottish Ornithologists' Club, in whose library the typescripts are now deposited, both for access to them and to many of the published journals from which other records of migrating geese were taken. Dr AEvar Petersen, Director of the Icelandic Institute of Natural History, Reykjavik, drew HB's attention to the collection of records of arrivals of birds in Iceland that had been made by the late Dr Finnur Gudmundsson and encouraged him to make use of it. Dr Trausti Jonsson, director of research and operations of Vedurstofa Islands, Reykjavik, allowed HB to copy many records and provided much helpful advice; he is not responsible for any errors of interpretation. Dr Julian Mayes, of the Department of Environmental and Geographical Studies, Roehampton Institute London, kindly provided us with a copy of his listing of daily weather systems over Scotland. HB is indebted to Dr P.Blancher, D. Bondy and J.A.Keith of the National Wildlife Research Centre, Canadian Wildlife Service, Ottawa, for financial support and encouragement to pursue international inquiries. We are grateful to Dr A.D.Fox for helpful comments on a draft. REFERENCES Bardarson, H.R. (198) Birds of Iceland. Bardarson, Reykjavik. Bell, M.V. (1988) Feeding behaviour of wintering Pinkfooted and Greylag Geese in northeast Scotland. Wildfowl, 39, Bell, M.V., Dunbar, J. & Parkin, J. (1988) Numbers of wintering Pinkfooted and Greylag Geese in northeast Scotland Scottish Birds,, 490. Bell, M.V. & Newton, S.F. (1995) The status and distribution of wintering Pinkfooted and Greylag Geese in east central Scotland. Scottish Birds, 18, Bergthorsson, P. (1985) Sensitivity of Icelandic agriculture to climatic variations. Climatic Change, 7, Bjornsson, H. (197) Fuglalif i Oraefum, A.Skaft. Bird life in the Oraefi area, S.E. Iceland. Natturufraedingurinn, 4, Boyd, H. & Fox, A.D. (1995) Abdominal profiles of Icelandic Pink footed Geese Anser brachyrhynchus in spring. Wildfowl, 4, Elkins, N. (1983) Weather and Bird Behaviour. Poyser, Calton. Fox, A.D., Gitay, H., Owen, M., Salmon, D.G. & Ogilvie, M.A. (1989) Population dynamics of Icelandnesting geese, Ornis Scandinavica, 20, Fox, A.D., Mitchell, C., Stewart, A., Fletcher, A.D., Turner, J.V.N., Boyd, H., Shimmings, P., Salmon, D.G., Haines, W.G. & Tomlinson, C. (1995) Winter movements and sitefidelity of Pinkfooted Geese Anser brachyrhynchus ringed in Britain, with particular emphasis on those marked in Lancashire. Bird Study, 41, British Trust for Ornithology, Ringing & Migration, 20, 3

14 Goose migration from Scotland to Iceland Fox, A.D. & Ridgill, S.C. (1985) Spring activity patterns of migrating Greenland Whitefronted geese in West Greenland. Wildfowl, 3, Hulme, M. & Barrow, E.(eds.) (1997) Climates of the British Isles present, past and future. Routledge, London. Lamb, H.H. (1972) British Isles weather types and a register of the daily sequence of circulation patterns Geophysical Memoirs, London, 1, 11, 184. Mayes, J. (1991) Regional airflow patterns in the British Isles. International Journal of Climatology, 11, Ogilvie, M.A. (1978) Wild Geese. Poyser, Berkhamsted. Santer, B.D. (1988) Regional Validation of General Circulation Models. Climatic Research Unit Publication, 9, University of East Anglia, Norwich. Williamson, K. (198) Goose emigration from western Scotland. Scottish Birds, 5(2), (MS received 11 January 1999; MS accepted 1 March 1999) 2000 British Trust for Ornithology, Ringing & Migration, 20, 3