Moult and moult migration of Greylag Geese Anser anser from a population in Scania, south Sweden

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1 Bird Study ISSN: (Print) (Online) Journal homepage: Moult and moult migration of Greylag Geese Anser anser from a population in Scania, south Sweden L. Nilsson, J. Kahlert & H. Persson To cite this article: L. Nilsson, J. Kahlert & H. Persson (21) Moult and moult migration of Greylag Geese Anser anser from a population in Scania, south Sweden, Bird Study, 48:2, , DOI: 1.18/ To link to this article: Published online: 29 Mar 21. Submit your article to this journal Article views: 229 View related articles Citing articles: 8 View citing articles Full Terms & Conditions of access and use can be found at Download by: [Lund University Libraries] Date: 22 March 217, At: 6:32

2 Bird Study (21) 48, Moult and moult migration of Greylag Geese Anser anser from a population in Scania, south Sweden LEIF NILSSON 1 *, JOHNNY KAHLERT 2 and HAKON PERSSON 1 1 Department of Animal Ecology, University of Lund, Ecology Building, S Lund, Sweden and 2 Department of Coastal Zone Ecology, National Environmental Research Institute, Kalø, DK-841 Rønde, Denmark The moult migration of Greylag Geese Anser anser from Scania, southernmost Sweden, was studied based on resightings of neck-banded individuals marked in the breeding areas. Most geese seen in moulting areas were recorded in the marking area both before and after moult. Up to 1992, 72% of all neckbanded Greylag Geese recorded from a moulting area were reported from Oostvaardersplassen in the Netherlands, 6 km from the marking area. After 1992, there was a change in the moult migration and the majority of the reports of moulting Greylag Geese from Scania were from the Danish island of Saltholm a distance of 5 km away. Owing to the increase in the Greylag Goose population, the moulting site at Oostvardersplassen probably reached its carrying capacity and the geese had to move their moult site. The moult migration of the study population is discussed in relation to the food availability of the two main moulting sites. Waterfowl are flightless for a number of weeks during moult and so require habitats with low probability of predator or quasi-predator (disturbance) encounters and a predictable and plentiful food resource. The gathering of young birds and failed breeders in traditional moult sites has long been a well-known feature, occasionally involving migration over considerable distances (see review by Salomonsen 1968). For the Greylag Goose Anser anser the first account was of a moult migration to Vejlerne in Denmark (Salomonsen 1968, cf. Paludan 1973). With the reclamation of Zuid-Flevoland from Lake Ijsselmeer in the Netherlands in 1968, a moult site for Greylag Geese became established at Oostvaardersplassen (Zijlstra et al. 1991, Van Eerden et al. 1997). Over the last 3 years, the Greylag Goose population in northwest Europe has increased dramatically (Fog et al. 1984, Madsen 1987, Nilsson et al. 1999). The number of moulting Greylags at Oostvaardersplassen has shown a similar trend, and *Correspondence author. leif.nilsson@zooekol.lu.se numbers eventually peaked at over 6 individuals in 1992 (Van Eerden et al. 1997). Furthermore, new moult sites for Greylag Geese were reported in the 198s from Gotland (Essen & Beinert 1982), Slonsk in Poland (Gromadzki & Majewski 1984), central Norway (Follestad et al. 1988) and recently on some other sites in Sweden, Denmark and Germany (Nilsson et al. 1999). Based on ring recoveries and observations of collared birds, geese at these moult sites were known to originate from different parts of the breeding range (Lund 1971, Essen & Beinert 1982, Gromadski & Majeski 1984, Zijlstra et al. 1991). In particular, it was established that Oostvaardersplassen was an important moult site for Swedish Greylags (Nilsson 1992). From 1992 onwards, numbers declined markedly at Oostvaardersplassen, probably as a result of habitat degradation and competition (Van Eerden et al. 1997). This coincided with the establishment of a moulting flock on the island of Saltholm in the sound between Denmark and Sweden, and resightings of large numbers of neck-banded Greylag Geese from 21 British Trust for Ornithology

3 13 L. Nilsson, J. Kahlert & H. Persson Scania in south Sweden at this site (Fox et al. 1995). Here, we use count surveys and the resightings of neck-banded individuals to describe the phenology of the moult migration of Greylag Geese from Scania to Oostvaardersplassen and the newly established moult site at Saltholm. We also consider the hypothesis that the establishment of Saltholm as a moult site resulted from a change in the tradition of moult migration. In particular, we assess the suitability of Saltholm as an alternative moult site with respect to predation/disturbance risk and the presence of a sustainable food resource when conditions at Oostvardersplassen were not able to meet the requirements of the extraordinarily large number of moulting Greylag Geese in the early 199s. METHODS The moult sites at Oostvaardersplassen and Saltholm are situated 61 and 5 km respectively from the breeding area in Scania (Fig. 1). At Oostvaardersplassen the Greylag Geese mainly feed on Reed Phragmites australis during moult (Loonen et al. 1991, Zijlstra et al. 1991, Van Eerden et al. 1997), whereas on Saltholm the geese mainly feed on Puccinellia maritima (Fox et al. 1998). To investigate whether the decline in the number of moulters at Oostvaardersplassen corresponded with an increase in numbers on Saltholm, count surveys from the two areas were compared during the period At Oostvaardersplassen, the number of moulting birds was established from a combination of calculating the turnover of neck- Tåkern Gotland SW Scania Saltholm Maribo Oostvaardersplassen Figure 1. Map showing the geographical position of moult sites for Greylag Geese marked in southwestern Scania during The marking area is indicated by an arrow.

4 Moult migration of Greylag Geese 131 banded geese in flocks prior to moult and aerial surveys during moult (Zijlstra et al. 1991). On Saltholm, the surveys were based on ground counts except in 1992 when an aerial survey was conducted. Neck-banding of Greylag Goose families (adults and their young) has been undertaken in southwestern Scania, southernmost Sweden, since 1984 (Persson 1994). The geese breed in eutrophic lakes situated in an agricultural landscape (Nilsson & Persson 1993, 1994, Nilsson et al. 1997). In all, 446 adults, 1315 goslings and 15 moulting non-breeders were neck-banded during the years (Persson 2). When resighted, the neck-banded individuals were regrouped as follows: the term yearlings designated birds hatched in the previous calendar year; subadults corresponded to birds in their third calendar year or older, that had never been recorded breeding; and adults were equivalent to birds that were known to have bred at least once (Nilsson & Persson 1994). The Scanian study area was visited at least twice weekly from the arrival of the Greylag Geese in February or March until the end of May, almost daily from 1 June and until the last gosling fledged in the middle of July and thereafter at least once a week until the geese left in November/December. At every visit, all goose flocks were checked for marked birds, and almost every neck-banded individual was identified. At the moult site Oostvaardersplassen, the searches for individually marked geese relied to some extent on a very active group of birdwatchers during the period On Saltholm, systematic searches (22 37 field days per year) for neck-banded geese were undertaken from about 2 May to 3 June, A number of moult sites used by smaller numbers of Greylag Geese are known from south Sweden, Denmark and north Germany (Nilsson et al. 1999). These moult sites were also checked for the occurrence of neckbanded individuals by a network of local ornithologists. RESULTS Phenology The Greylag Geese from southwestern Scania are highly philopatric (Nilsson & Persson unpubl. data), and the majority of the birds resighted in different moulting areas were recorded in southwestern Scania both before and after the moult (Tables 1 3). In total, 88% of the adults seen moulting at Oostvaardersplassen were resighted in Scania earlier the same season compared to 75% for yearlings and 76% for subadults (Table 1). In all years, a gradual disappearance of marked individuals was noted from early April, followed by a marked departure in late May (Fig. 2). Several birds moulting at Oostvaardersplassen arrived there a few days after their departure from southwestern Scania. For two individuals the first reading in Oostvaardersplassen was reported the day after the bird was last seen in Scania. After the moult period, at least 87% of the adults seen at Oostvaardersplassen returned to southwestern Scania compared to 49% of the yearlings and 64% of the subadults (Table 2). The first moulting birds from Oostvaardersplassen returned to southwestern Scania at the beginning of July and by mid-july about 5% had returned (Fig. 3). A few observations in staging areas between Oostvaardersplassen and southwestern Scania have been reported (Table 2), but most returning geese seem to migrate directly to Scania. As for the Greylag Geese moulting in Oostvaardersplassen, the majority of those marked in Scania and moulting on Saltholm were resighted in southwestern Scania both before and after the moult (Table 3). Less than 3% of the Greylag Geese moulting on Saltholm had Table 1. Number of neck-banded Scanian Greylag Geese sighted in different areas in spring before moulting at Oostvaardersplassen. Accumulated totals for the years Number of geese in different age groups Area Yearlings Subadults Adults Total Scania Sweden N of Scania 1 1 Norway 1 1 Denmark The Netherlands West Germany 1 1 Not seen before moult Total

5 132 L. Nilsson, J. Kahlert & H. Persson Table 2. Number of neck-banded Scanian Greylag Geese resighted in different areas in summer and early autumn after moulting at Oostvaardersplassen. Accumulated totals for the years Number of geese in different age groups Area Yearlings Subadults Adults Total Scania only Denmark and Scania West Germany and Scania East Germany and Scania Denmark only West Germany and Denmark West Germany only 2 2 East Germany only The Netherlands only Not seen again this year 5 5 Never seen again Total Table 3. Number of neck-banded Scanian Greylag Geese observed on Saltholm during moult and percentage seen in Scania before and after the moult on Saltholm. Accumulated totals for the years Percentage seen in Scania Age group Numbers on Saltholm Before moult After moult Yearlings Subadults Adults already left southwestern Scania in early spring but the majority remained until May (Fig. 2). The post-moult dispersal from Saltholm started in the middle of June in all years (Fig. 3) and continued until the end of June. The Greylag Geese reappeared in Scania shortly after they had left Saltholm. About half of the returning Greylags were resighted before mid- July, but some individuals were not seen before August and September. Moulting at Oostvaardersplassen Up to 1992, 72% (n = 27) of all neck-banded, non-breeding Scanian geese reported from moulting places were reported from Oostvaardersplassen. During , the proportion of potential moulting geese among yearlings and subadults using this moult site were in the ranges 5 42% and 5 37%, respectively (Fig. 4). Both these categories showed a marked annual variation, whereas the proportion of former breeders recorded moulting at Oostvaardersplassen showed less variation, ranging from 27% to 37% during this period. The number of Scanian birds resighted in Oostvaardersplassen from 1993 onwards was much lower for all categories, i.e. 14% of all moulting non-breeders. Moulting on Saltholm During , between 22 and 43 neckbanded Greylag Geese from Scania were found moulting on Saltholm (Table 4). The proportion of marked non-breeders seen on Saltholm during moult varied markedly between years, in particular for yearlings (Fig. 4). The proportion of former breeders moulting on Saltholm showed a slight increase during the study period. During , 24% (n = 91) of the moulting birds from southwestern Scania seen on Saltholm were adults compared to 36% (n = 132) during , the difference being

6 Moult migration of Greylag Geese Cumulative proportion of last resightings in Scania (%) April May June Five-day periods Figure 2. Last resighting dates per five-day period (cumulative percentage) of neck-banded Greylag Geese in southwestern Scania, which were subsequently found moulting:, at Oostvaardersplassen in (n = 15);, on Saltholm in (n = 133). significant (χ 2 = 3.29, Yates correction, df = 1, P <.5). There is thus some evidence to suggest that the use of Oostvaardersplassen has decreased in importance for moulting Scanian Greylag Geese, whereas the numbers moulting on Saltholm have increased (Fig. 5). Other moulting sites Between 2% and 14% of the potential moulting geese stayed to moult together with the families in the study area in southwestern Scania (Table 4). This proportion showed a slight increase during the study period from 4.% (n = 792) during the years to 6.8% (n = 959) during the years , the difference being significant (χ 2 = 6.21, Yates correction, df = 1, P <.5). By contrast, the whereabouts of the geese that departed southwestern Scania is mostly unknown, with the exception of those seen moulting at Oostvaardersplassen or Saltholm. The proportion 1 9 Cumulative proportion of last resightings in Scania (%) June July August Five-day periods Figure 3. First resighting dates per five-day period (cumulative percentage) of neck-banded Greylag Geese back in southwestern Scania after moult:, at Oostvaardersplassen in (n = 64);, on Saltholm in (n = 156).

7 134 L. Nilsson, J. Kahlert & H. Persson a a 65 Proportion of moulters (%) 5 b b c Year Figure 4. Percentage of potential moulters among neck-banded Greylag Geese of different age groups seen in Scania, that were actually seen moulting at Oostvaardersplassen ( ) and Saltholm ( ) in (a) Subadults; (b) yearlings; (c) adults. The number of potential moulters is given above the bars. Note that observations on Saltholm started in c 56 reported from these other sites was significantly higher during the years than during the years (3.9% vs. 1.7%; χ 2 = 8.37, Yates correction, df = 1, P <.1). Seven individuals were reported from the island of Gotland (Fig. 1). Observations in southwestern Scania during spring and autumn of Greylag Geese marked as moulting geese on Gotland suggest that this area was used as a moult site for geese from southwestern Scania. One goose was regularly found moulting with a small flock in the province of Hälsingland, central Sweden. Moreover, 17 individuals were found at the Maribo lakes in Denmark and four in northern Germany. In fact, the Maribo lakes were used as a moulting site for a number of Greylag Geese from Scania after the first decline at Oostvaardersplassen. In 1998, nine individuals were found moulting in Lake Tåkern in south central Sweden (Fig. 1), where previously only five individuals from southwestern Scania had been resighted during moult. Two observations of Scanian Greylag Geese were obtained from moult sites in central Norway. Further support for this migration route was given by resightings of two neckbanded Greylags in the province of Värmland, west central Sweden. Moreover, three individuals marked as moulting birds in Norway were resighted in southwestern Scania. Change in moult migration There are indications that Oostvaardersplassen reached its carrying capacity as a moulting area

8 Moult migration of Greylag Geese 135 Table 4. Number of moulting, non-breeding, neck-banded Greylag Geese sighted. Yearlings Subadults Adults Year Sc Fl Sa Ma Os Sc Fl Sa Ma Os Sc Fl Sa Ma Os Total Key to locations: Sc, study area in Scania; Fl, Oostvaardersplassen in Flevoland, the Netherlands; Sa, Saltholm, Denmark; Ma, Maribo lakes, Denmark; Os, other sites. Observations on Saltholm started in in , as 7 to 15 Greylag Geese were seen arriving there only to leave shortly afterwards in another direction (Van Eerden et al. 1997). In 1989, one Greylag Goose that was seen in southwestern Scania until 8 May was seen at Oostvaardersplassen between 23 and 3 May and back in southwestern Scania on 5 June, moulting with the breeders at the latter site. Among neck-banded Scanian Greylag Geese reported from moult sites in more than one season, 88% (n = 73) moulted at the same site in Numbers in Oostvaardersplassen Numbers on Saltholm Figure 5. Number of moulting Greylag Geese in Oostvaardersplassen in relation to the number of moulting geese on Saltholm successive years. Of 35 individuals moulting in Oostvaardersplassen seen at a moult site during two years, six were found on Saltholm the second time, and one at Maribo. One Greylag Goose moulting on Saltholm was found moulting at Lake Tåkern in a second year. Two Greylag Geese marked as moulting birds on Gotland were later found moulting on Saltholm. Moreover, one goose marked in Scania was found moulting at Lake Tåkern in 1992, and later moulting on Saltholm. During the same period in which the frequency of Scanian birds moulting at Oostvaardersplassen decreased, the total population of Greylag Geese moulting in Oostvaardersplassen also showed a decrease. The annual counts at Oostvaardersplassen and Saltholm showed an inverse relationship since 1992 (Spearman s r s =.82, P <.4, n = 7, Fig. 5), supporting the hypothesis that a shift in the distribution of moulting geese from Flevoland to Saltholm had occurred. The change of moult site from Oostvaardersplassen to Saltholm had a marked effect on how long the geese were away from southwest Scania each year. Median departure dates for Greylag Geese from Scania moulting at Oostvaardersplassen and Saltholm respectively were 5 May and 7 May (Fig. 2), i.e. virtually the same dates. After the change of moulting site, the geese were back in southwestern

9 136 L. Nilsson, J. Kahlert & H. Persson Scania much earlier (median of first resighting date in south Scania was 18 July and 8 July for Oostvaardersplassen and Saltholm, respectively (Fig. 3), the difference being highly significant (Wilcoxon two-sample test, Z = 12.33, P <.1)). Based on the median dates, the time elapsing between last and first resighting date in southwestern Scania decreased from 74 to 62 days. DISCUSSION In the present study, the importance of Oostvaardersplassen as a moult site for Greylag Geese from southern Sweden until a few years ago was confirmed, as a high proportion of the potential moulting geese from the population in southwestern Scania was resighted at Oostvaardersplassen during the moult period. Up to 1992, few moulting Greylag Geese from southwestern Scania were reported from other sites. It thus seems likely that the majority of the moulting Greylag Geese from southwestern Scania migrated to Oostvaardersplassen, the key European moult site for the species at that time (Zijlstra et al. 1991, Van Eerden et al. 1997, Nilsson et al. 1999). The increasing numbers of moulting Greylag Geese, reflecting a general increase in the Greylag Goose population of northwest Europe (Nilsson et al. 1999), exerted a heavy grazing pressure on the reed-beds at Oostvaardersplassen, leading to marked intraspecific competition for food. Studies also showed that goose grazing actually degraded the food stock and reduced the size of high quality Phragmites areas for moulting Greylags (Van Eerden et al. 1997). Geese were therefore forced to use internal fat reserves to an increasing extent during the moult (Van Eerden et al. 1997), and during the years reverse migrations of between 7 and 15 Greylag Geese were noted annually. Management measures allowed the population to increase further to a peak of 6 moulters in 1992 (Koffijberg et al. 1997). From 1992 onwards, the number of moulting Greylag Geese in Oostvaardersplassen decreased dramatically, reaching about 2 in During this period, Saltholm became established as one of the most important alternative moult sites. The number of moulting birds on Saltholm showed a steady increase since the studies started, from about 6 in 1992 to birds in June It is not precisely known when the birds started to use Saltholm as a moult site, but it was assessed most likely to have occurred in the mid- to late 198s (Fox et al. 1995). A number of other moult sites were also established, e.g. at the Maribo lakes in Denmark and in Schleswig-Holstein (Koop 1998) and at Lake Tåkern in Sweden (Fig. 1). With the decrease in numbers of moulting geese at Flevoland and the establishment of Saltholm as a new moult site, the proportion of Scanian moulting geese seen at Oostvaardersplassen decreased markedly, and very few individuals were seen there from 1993 onwards. Simultaneously, an increasing proportion of potential moulting geese was found moulting on Saltholm. In 1997, this proportion was on the same level as at Oostvaardersplassen before the overexploitation of the moult site. During , the proportion of adults resighted at Oostvaardersplassen during moult remained fairly constant in spite of the large numbers of geese seen on reverse migration. By contrast, the proportion of yearlings showed much more variation. Older birds may have been dominant to yearlings in the competition for food at the moult site when food resources became less available (Gregoire & Ankney 199), or they may have had higher site-fidelity than younger geese which were able to change moult site when conditions deteriorated. This was also supported by the fact that the proportion of adults seen on Saltholm was higher in than during the first three years of the study, which indicates that the older birds changed to the new site later than the young ones. The change of moult site for the main part of the study population might have an overall effect on the population, as both flight and moult are energy-consuming. During the first years of the study the Greylag Geese migrated about 6 km to moult at the traditional moulting place at Oostvaardersplassen instead of migrating 5 km to Saltholm for the moult. The later return to southwestern Scania after moulting in Oostvaardersplassen compared to moulting on Saltholm may result from the need to restore fat reserves prior to the return flight. Another explanation may be that the protein content of Puccinellia, the major

10 Moult migration of Greylag Geese 137 food on Saltholm, falls below that of other potential food items on the island after about 2 June, leading to a quick dispersal once the geese are able to fly (Fox et al. 1998). Phragmites, the major food in Flevoland, also deteriorates during the summer (Van Eerden et al. 1997, Loonen et al. 1997) but maintains a higher protein content for longer than Pucinellia on Saltholm, potentially allowing the geese to stay for a longer period before returning to southwestern Scania after the moult. As the Greylags started to moult at other sites when Oostvaardersplassen reached its capacity, Scanian Greylags to some extent started to moult at the Maribo lakes in southern Denmark, another Phragmites area, before the moulting tradition was established on Saltholm. After a few years the Maribo lakes lost its importance for Scanian Greylags, probably being used to capacity by the local breeding birds. During recent decades, with markedly increasing populations of Greylag Geese in northwest Europe, changes in moulting sites have been recorded (Ouweneel 1978, Nilsson et al. 1999). Whereas detailed studies are lacking in most cases, the change from Oostvaardersplassen for some of the moulting geese was clearly related to habitat degradation and competition among the increasing number of Greylag Geese (Van Eerden et al. 1997). Recently there have been indications that Saltholm as a moulting site is also filling up with Greylags, and more Greylags from Scania went to Lake Tåkern for the moult in What will happen next? Moulting geese require safe feeding areas with adequate food resources during the flightless period. The known moulting sites in Europe in recent decades are few (Loonen et al. 1991, Nilsson et al. 1999) and nearly all are situated either in extensive reed beds or on offshore islands. Will there be sufficient high quality moulting sites to harbour the increasing numbers of young Greylag Geese in northwest Europe or will the population increase be limited by factors operating in the breeding, wintering or staging areas? REFERENCES Essen, L. von & Beinert, R Moulting A. anser along the Gotland coast. Aquila 89: Fog, M., Lampio, T., Myrberget, S., Nilsson, L., Norderhaug, M. & Röv, N Breeding distribution and numbers of Greylag Geese Anser anser in Denmark, Finland, Norway and Sweden. Swed. Wildl. Res. 13: Follestad, A., Nygård, T., Röv, N. & Larsen, B.H Distribution and numbers of moulting non-breeding Greylag Geese in Norway. Wildfowl 39: Fox, A.D., Kahlert, J., Ettrup, H., Nilsson, L. & Hounisen, J.P Moulting Greylag Geese Anser anser on the Danish island of Saltholm; numbers, phenology, status and origins. Wildfowl 46: Fox, A.D., Kahlert, J. & Ettrup, H Diet and habitat use of moulting Greylag Geese Anser anser on the Danish island of Saltholm. Ibis 14: Gregoire, P.E. & Ankney, C.D Agonistic behavior and dominance relationships among lesser snow geese during winter and spring migration. Auk 17: Gromadzki, M. & Majewski, P The migrations of the Greylag Goose, Anser anser, in Poland. Acta Sci. Nat. Brno 18(1): Koffijberg, K., Voslamber, B. & Van Winden, E Ganzen en zwanen in Nederland: overzicht van pleisterplaatsen in de periode SOVON Vogelonderzoek Nederland, Beek-Ubbergen. Koop, B Die Bedeutung der Binnengewässer Schleswig-Holsteins als Mauserquartiere für Wasservögel die Ergebnisse einer landesweiten Erfassung Corax 17: Loonen, M.J.J.E., Zijlstra, M. & Van Eerden, M.R Timing of wing moult in Greylag Geese Anser anser in relation to the availability of their food plants. Ardea 79: Lund, H.M-K Ringmerking av Grågjess i Norge. Sterna 1: Madsen, J Status and management of goose populations in Europe, with special reference to populations resting and breeding in Denmark. Dan. Rev. Game Biol. 12: 4. Nilsson, L Flevoland an important moulting and staging area for Nordic Greylag Geese. Vogels in Flevoland 1: Nilsson, L. & Persson, H Variation in survival in an increasing population of the Greylag Goose Anser anser in Scania, southern Sweden. Ornis Svecica 3: Nilsson, L. & Persson, H Factors affecting the breeding performance of a marked Greylag Goose Anser anser population in south Sweden. Wildfowl 45: Nilsson, L., Persson, H. & Voslamber, B Factors affecting survival of young Greylag Geese Anser anser and their recruitment into the breeding population. Wildfowl 48:

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