Tijsen W.,Poelweg 12 |
Koffijberg K.,Sovon Vogelonderzoek Nederland
Limosa | Year: 2015
In the northern part of the province Noord-Holland, close to the western Wadden Sea and Lake Usselmeer, large numbers of geese and swans roost in the polders of Wieringermeer and on the former island of Wieringen and the adjacent Balgzand area. The area is mainly in agricultural use (Fig. 1). Swans and geese predominantly feed on harvest remains of sugar beet and potatoes, on Wieringen mainly on grassland. The area is highly attractive to swans and geese as the feeding areas are well in reach of suitable night-roosts (Fig. 2 & 3). This paper describes the occurrence of geese and swans in the area in the past decades and tries to explain some observed trends with known changes in land-use. Both from a national perspective as well as in an international flyway context, Bewick's Swan Cygnus bewickii and Tundra Bean Goose Anser serrirostris are the most important species occurring in the region. For Bewick's Swan numbers amounted to up to 11% of the flyway population (Tab 1.). Numbers in this species initially remained on a high level, while the size of the flyway population and the numbers in The Netherlands started to decline in the mid-1990s (Fig. 4). After 2006/07 also in the Wieringermeer a sharp decline occurred (Fig. 4). Nowadays, only small numbers are observed. Although a separate study showed a local impact of the establishment of a new windpark, it is unlikely that establishment of a large windpark in 2006 caused the decline of the swans. Changing migration and wintering strategies (indicating an eastward movement of the winter range) are more likely drivers for the observed patterns. Numbers of Tundra Bean Geese have continued to increase (Fig. 6), even at a higher rate than the national trend, and in contrast to a decline at other sites in the Wadden Sea area, which has rendered the Wieringermeer (together with the island of Texel) a rather isolated staging area in the northwestern part of The Netherlands. Numbers peak in December (Fig. 7), after which at least part of the geese leave for staging areas in the northeastern part of The Netherlands, or even in the eastern part of Germany (as shown by individually marked geese). The increase of Tundra Bean Goose occurred in a period where food availability declined (Fig. 1), but obviously not to an extent that affected the numbers of geese. Brent Geese, mainly Dark-bellied Brent Goose Branta bernicla, occur mainly on the former island of Wieringen. Their distribution on the island has changed slightly in the past decades, possibly linked to the strong increase in year-round present Greylag Geese Anser anser, which compete with Brent Geese, but also facilitate Brent Geese in spring by keeping the sward of the grasslands suitable for them. During influxes in cold winters, Wieringen also becomes one of the most important winter roosts of Light-bellied Brent Geese B. hrota in The Netherlands. In 2009/10 up to 3% of the flyway population was observed in the area. Occurrence of Light-bellied Brent Geese on Wieringen has also been documented in the past (1920-1930), both in cold and normal winters.
Boele A.,Sovon Vogelonderzoek Nederland
Limosa | Year: 2012
The Black-winged Stilt is a rare but regular breeding bird in The Netherlands, with the first known breeding attempt in 1931 and 20-40 pairs in peak years (Fig. 1). In 1990-2011 (22 years, 210 breeding pairs in total) the species has bred every year except for 1996 and 2003. In 1931-1989 (59 years, 227 breeding pairs) breeding attempts were found in 'only' 32 years with possible breeding in four other years. This difference most probably also reflects the (growing) number of bird watchers and a more systematic data collection in recent years. The Delta area, more specifically the province of Zeeland, in the SW-Netherlands, normally holds most of the breeding birds (Figs. 1-3; Table 1) but the proportion of pairs breeding in the northern part of the country is growing (Fig. 3). With a provisional total of 24 pairs, 2011 was the best year since 1999-2001. In 2011 a relatively large proportion bred in the North of the country (Fig. 3). There is a negative correlation between the amount of precipitation in January-April in Mediterranean France and Spain and the number of Black-winged Stilts breeding in The Netherlands, with more breeding attempts in drier years (Fig. 4). 84% of the breeding attempts in 1931-2011 took place in years with below-average rainfall in Spain and Southern France.
Increase of wintering great white egrets casmerodius albus in the netherlands as shown by diurnal counts and roost counts [De toename van overwinterende Grote Zilverreigers in Nederland aan de hand van dagtellingen en slaapplaatstellingen]
Klaassen O.,Sovon Vogelonderzoek Nederland
Limosa | Year: 2012
This paper describes the development of numbers of Great White Egret wintering in The Netherlands since 2000/01, based on multiple data sources: non-systematic observations, monthly waterbird counts and dedicated counts at night roosts.The latter were initiated in 2003/04 but national coordination and coverage was only achieved some years later (Tab. 1). In recent years, Great White Egrets are found wintering throughout the country (mainly in farmland and marshlands), but the regions that were occupied first still hold the highest densities (Fig. 3)- Within the wintering period movements must occur, since different provinces show of four different seasonal patterns, with a peak in autumn (3 provinces), in mid-winter (3) or at the end of the winter (5). The province holding the only Dutch breeding colony, Flevo-land, shows a very different pattern with the lowest numbers in (early) winter (Fig. 4). Foraging behaviour changes in the course of the non-breeding season, with aquatic foraging predominant in autumn (when egrets sometimes follow fishing flocks of Great Cormorant Phalacrocorax carbo) followed by a switch to land-based foraging in winter, with Common Voles Microtus arvalis as an important prey. The strongly increasing trends in numbers based on non-systematic observations and waterbird counts are very similar (Fig. 1). Roost counts yielded the highest numbers, exceeding those from the waterbird counts by 32% on average.during the four most recent winters. The number of known roost sites has also increased, particularly that of small roosts with less than 10 birds (Fig. 5). Between 2003/04 and 2010/11, in total 221 roost were found, among which 30 with more than 50 birds, including 9 with more than 100 (maximum at a single roost 917 during a frost in February 2012). Of the three data sources, the waterbird counts provide the most reliable trend indices and seasonal patterns, the roost counts the most comprehensive population estimates, and the non-systematic observations add significantly to the distribution pattern. An estimate for the national wintering population in 2010/11 arrived at 2300-2800 birds. This alone indicates that the growing Dutch breeding population, currently comprising about 150 pairs, cannot be the single source of the increase. This is corroborated by a growing number of colour ring resightings, mainly from France but also from Poland. From data on breeding numbers and ringing results elsewhere in Europe, a pattern emerges of a decreasing traditional breeding population in Austria/Hungary with a southern winter range, and newer more northerly breeding populations in France, The Netherlands, Poland, Ukraine and Belarus which show a strong increase and of which the birds winter at roughly the same latitudes, but partly make extensive westward movements.
Nolet B.,Netherlands Institute of Ecology |
Kolzsch A.,Netherlands Institute of Ecology |
Oosterbeek K.,Sovon Vogelonderzoek Nederland |
De Vries P.,Netherlands Institute of Ecology
Limosa | Year: 2014
In the classical approach, counts are used to designate sites as important stopovers of migratory birds. Now that individual birds can be tracked on migration by high-tech means, we can also determine which sites are visited most often and/or for the longest periods by tagged birds. The advantage of this alternative method is that remote places will not be underrepresented. Here we illustrate this method with data of Bewick's Swans Cygnus bewickii carrying GPS loggers. In winter 2010/11 a total of 30 Bewick's Swans were caught with cannon nets. Of these, 13 adult females were equipped with neck collars with built-in GPS data-logger (75 g in total), which logged GPS locations (<5 m accurate) eight times a day. Upon returning the next winter, these swans were traced with the help of volunteer observers, and the data downloaded via blue-tooth connection. In total, seven year-round tracks were obtained. A heat-map of the first half of the calendar year revealed clear hotspots in Germany (Emsland and Lower-Elbe/Schleswig-Holstein) and in Estonia, and a smaller one in the Dvina Bay of the White Sea (Fig. 2). A heat-map of the second half of the year showed a hotspot in the Korovinskaya Bay in northern Russia, and in Estonia and Latvia, and further on along the Middle Elbe and in the Netherlands (Veluwemeer, Fig. 3). In general, these stopovers are in close agreement with those determined using the classical approach, the exception being the Dvina Bay (White Sea). This site is visited by a large proportion of the population, but stopover duration is only short. Estonia is borne out to be the major spring board to the breeding grounds in northern Russia.
Wintering of Hen Harriers Circus cyaneus in Southern Limburg; Do hamster reserves form an ecological trap? [Overwinterende Blauwe Kiekendieven in het Limburgse heuvelland: Vormen hamsterreservaten een ecologische val?]
De Boer P.,Sovon Vogelonderzoek Nederland |
Voskamp P.,Provincie Limburg |
Van Rijn S.,Ida Gerhardtsingel 65
Limosa | Year: 2013
The ecology of Hen Harriers wintering in the southern part of the province of Limburg, Netherlands, was studied in the winters of 2010/11 and 2011/12. Prior to 2004 Hen Harriers used to be scarce in the study area, dominated by intensive farming. The establishment of 400 ha of arable land with a special management for Hamsters Cricetus cricetus created unprecedentedly high numbers of Common Voles Microtus arvalis as a side effect. This food bonanza attracted many predators, including Hen Harriers. Initially the main focus of this study was on the occurrence of roosts, diet and habitat use. Habitat use was determined by tracking birds fitted with radio transmitters. Roosts were detected the same way and by simply following birds leaving the feeding grounds. Diet was determined by pellet analysis. Roosts were counted simultaneously where possible. In total a maximum of 48 Hen Harriers was counted on ten different roosts. Numbers on large roosts (8-10 birds) appeared to be more stable than those on smaller ones. One bird regularly roosted in trees. The diet showed little variation, 98% of the prey items being Common Voles. The radio-tracked birds showed a preference to for hunting in hamster management areas, consisting of non-harvested crops like winter wheat and lucerne. Calcareous grassland reserves were visited frequently as well. A possible downside appeared with the finding of a depredated Hen Harrier in 2008 in one of the hamster reserves. Subsequently this the central part of the reserve was systematically searched for signs of depredation during four consecutive winters resulting in a total number of 10 dead Hen Harriers in 2007-2012. Seven birds were depredated, six probably by Red fox Vulpes vulpes and one by Goshawk Accipiter gentilis. Given the seasonal maximum numbers of roosting birds, this yields a mortality rate of ca. 18%, which raises the question whether an ecological trap was created. On the other hand modern intensive farming probably offers poor foraging conditions for wintering Hen Harriers wintering near safer roost sites in wetland habitats.