De Levende Natuur nummer 1 van 2010 (English summary)


Ganzen in Nederland en Vlaanderen


DLN 2010-1

Wintering and migratory geese in The Netherlands

K. Koffijberg, J.H. Beekman, F. Cottaar, B.S. Ebbinge, H.P. van der Jeugd, J. Nienhuis, D. Tanger, B. Voslamber & E. van Winden

The Netherlands support one of the biggest concentrations in goose numbers in Western-Europe. Monthly goose counts show that peak-numbers during midwinter have increased to an average 1,8 million individuals. These include major proportions of the flyway populations in Pink-footed goose, European white-fronted goose and Barnacle goose. The geese are attracted by favourable wintering conditions, like mild winters, high-quality feeding opportunities and numerous waterbodies that serve as safe night-roosts. The increase in numbers in The Netherlands is a result of global population growth in most species, which has been commonly attributed to a combination of improved protection and lower hunting pressure and favourable feeding conditions on agricultural land, where in the past decades both improved pastures and crops have attracted increasing numbers of geese to feed. The increase in numbers in The Netherlands, which is highest in (re-)introduced Greater Canada geese and Lesser white-fronted geese, and in natural Greylag geese and Barnacle geese, results from both an increase in peak numbers and an expansion of the period of stay during winter. Exceptions are Dark-bellied brent geese and Taiga bean geese which have declined in number. Advanced autumn migration has occurred markedly in Tundra bean goose and European white-fronted goose, nowadays reaching peak numbers already by Mid-November (formerly Mid-December). On the other hand, arctic-breeding Barnacle geese have delayed departure in spring by six weeks since 1988 and nowadays depart Mid-May, just ahead of Dark-bellied brent geese. Moreover, both Greylag goose and Barnacle goose meanwhile have established large breeding populations in The Netherlands, that also contribute to higher numbers outside the usual peak-occurrence in midwinter. Contrary to the extreme parts of the wintering range, like UK in the southwest or southern Sweden in the north-east, only weak evidence has been found that national distribution patterns have changed as a result of climate change. However, recent counts suggest a decline in Tundra bean goose in the SW-Netherlands in midwinter. Mass-departures in Tundra bean goose and European white-fronted goose in January in some years also support a tendency to advance spring migration.

Numbers and trends of wintering geese in Flanders

K. Devos & E. Kuijken

During the last 50 years Flanders has become increasingly important as a wintering area for wild geese, mainly White-fronted geese and Pink-footed geese (with up to 80 % and more of the Spitsbergen population; nowadays diminished to 50% or less). The distribution area of wild geese in Flanders is mainly limited to the polder areas along the coast and river Scheldt and floodplains along IJzer and Maas. The ‘Oostkustpolders’ are by some distance the most important goose area and account for an average of 63% of the total number of ‘goosedays’ in Flanders.
Especially since the beginning of the 1990s, there has been a clear increase in the number of geese, but since 2001/02 this trend seems to have stabilised. The total number of goosedays in Flanders has increased approximately fourfold since 1990. All goose species show the same increasing trend. The greatest increase is to be found in the Greylag goose.
Often situated at the southern border of the European winter range of several species, Flemish wintering areas could experience a strong impact of distribution shifts as a result of climate change.

The role of grasslands under nature conservation for wintering geese in The Netherlands

D. Bos, Th. Boudewijn & J.P. Bakker

Quite a large proportion of the geese wintering in The Netherlands is foraging on grasslands managed for nature conservation. We investigated the use of these grasslands by geese using dropping counts per area, and compared these to utilization of intensively managed fields for agriculture within so-called accommodation areas. On an annual basis we found no differences between these intensively managed grasslands and grasslands under nature conservation, however the seasonal pattern differs. We also show seasonal data on salt marshes and grasslands managed for botanical purposes. The use of salt marshes is characterized by two seasonal peaks in autumn and spring. The dropping counts revealed that the grazing intensity by geese declines, with increasing distance from a roost. We discuss the role of grazing with livestock and fertilizer application on foraging conditions for geese. Grazing and fertilizer application may significantly enhance terrain use by geese, as measured for Brent and Barnacle geese in several field studies. When fertilizer application is ceased, for example because of inconsistency with other nature conservation objectives such as botanical targets, this affects the capacity of the area on nutrient-poor soils. However, on two sites with nutrient-rich soils we did not yet find a decline in grazing intensity by geese, after fertilizer application ceased many years before. Two positive aspects of grasslands under nature conservation are that they often offer relative disturbance-free conditions, and that they are often located close to traditional roosting places. On a per area basis there is a high potential grazing intensity. Thus, the role of grasslands under nature conservation for accommodating geese should not be underestimated. The ecological objectives of many of these areas are in practice not specifically focused on geese, but this is no problem as long as the grass sward remains in a suitable condition.

Increasing goose numbers, increasing costs?

F.P.J. van Bommel & T.M. van der Have

Both the number of wintering geese as the breeding populations of geese have increased in The Netherlands. This has lead to a substantial rise in costs for compensation of agricultural damage and management for accommodating wintering geese. Therefore the question rises, if the increase in costs is in proportion to the population trends? Since the introduction of governmental policy to concentrate wintering waterfowl in designated accommodation areas, the costs have roughly doubled, to 14 million euro annually, whereas the numbers of wintering geese have been relatively stable. This increase is merely due to management costs and for damage payments. The majority of the management costs can be reduced by accommodating geese throughout The Netherlands in autumn and winter; the variable costs might be reduced to some degree by scaring high concentrations of geese away in late winter. For breeding populations the costs for compensation of agricultural damage have risen proportionally with the population trends, to 1.2 million euro in 2008. The expectation is that both numbers of breeding geese and costs further increase the coming years.

Taking care of wintering geese and Wigeons: evaluation of a new policy

F.F. van der Zee, D. Bos, Th.C.P. Melman, P.J. van der Reest, R.H.M. Verhoeven & M. Wesselius

On a European scale The Netherlands are the most important wintering area for geese and Wigeons. Over the last decades the goose populations have nearly all increased dramatically. As these birds are feeding mainly on agricultural pastures and fields, the conflict with agriculture has also been intensified. Starting in 2005, the Dutch policy to handle this conflict is to design 80.000 ha extra as ‘goose foraging areas’ for wintering geese on agricultural land. Within these areas the geese are hosted rather than scared away and the disturbance is minimized. The farmers who own the area get paid to compensate the measurements they have to take for hosting the geese (agri-environment schemes). The aim of this policy is a) enduring conservation of wintering geese and wigeon populations b) control of the agricultural damage and costs. To teach more geese to stay in the foraging areas, chasing away and regulated hunting is allowed only outside the foraging areas. After four years this new policy is evaluated. The main conclusions of this evaluation research are: 1. About 60% of the geese stay in the foraging areas. Unfortunately this number has not increased after four years of the new policy. 2. The total amount of foraging area is sufficient to accommodate the 2 million wintering geese and 800.000 wintering Wigeons in The Netherlands.
3. The costs of this new policy have increased from €8 million to €17 million per year. This increase is caused by the substantial payment of the farmers, estimation-costs and to the fact that the costs of damage outside the foraging areas did not decrease.

Recommendations to improve the new policy are given.

The protection of wintering geese in Flanders (Belgium)

E. Kuijken

After the discovery of wintering geese near Damme and Brugge in February 1958 the author could study the development of this phenomenon in the Oostkustpolders during half a century.
After the harsh winter 1978/79 and cold spells in the 1980s the increasing goose numbers (mainly White-fronted geese (Anser albifrons) and Pink-footed geese (Anser brachyrhynchus) spread out over larger polder areas in Flanders. This was enhanced by the national goose shooting ban since 1981 and resulted in a further increase during the 1990s. Both species prefer complexes of wet permanent grasslands but an increasing foraging on silage grass, winter wheat and crops after harvesting is a result of the ongoing conversion of former grasslands. The overall grazing pressure of geese remains low (av. 275 goosedays/ha; in core areas 750gd/ha) so the number of complaints by farmers is still limited. This is also caused by the complicated juridical procedure (leading to tax reduction), which is recently changed in an administrative assessment of damage. In order to reduce complaints caused by ‘summer geese’ the shooting of Graylag (Anser anser) and Canada goose (Branta canadensis) is temporarily allowed. The continued shooting ban on Arctic geese results in a spontaneous spreading of these birds. In the Oostkustpolders on average 73% of geese winter within Natura 2000 ‘special protection areas’ (fig. 2). In some designated areas with high bird numbers all hunting is prohibited from mid-November on, thus increasing the regional carrying capacity and safe wintering of waterbirds.
The most important threat for geese is habitat loss, mainly wet permanent grasslands. Positive are projects of nature restoration, often stimulated by EU-LIFE funding, and supported by an increasing public interest. Some indications exist that global warming could cause some distribution changes at flyway level.

Tracking marked geese over continental Europe

A special website has been developed to allow volunteer observers to enter observations of marked geese. The website has a general part open to everyone, and a part only accessible for registered observers. The latter part grants each observer access to observations of the geese he/she has observed him/her self.
The exact locality where one observes a goose has to be entered using google-maps.
The website now handles 7 goose species that occur in continental Europe, viz. Dark-bellied brent goose, Barnacle goose, Greater white-fronted goose, Bean goose, Pink-footed goose (Svalbard population), Greylag goose and Canada goose.
Registered observers can enter their sightings of geese marked with engraved colour-rings or neckbands, and get feedback about where these marked birds were ringed and spotted by other observers. If the bird you have seen matches an existing bird in our database you can immediately find the ringing information as well as information about other sightings of this same bird, plotted on a map. Currently the database holds ringing information of well over 50,000 individually marked geese over 1,000,000 resightings of these birds, made by a total number of 1690 different registered observers.
Special care is taken to collect the data in such a way, that the reliability of the data can be checked to some extent, to assess the quality later for data analysis.
This information on individually marked geese is vital to estimate annual survival rates, and life-time reproductive success, to study spatial and temporal distribution and help the estimation of population sizes.

Breeding goose populations in The Netherlands

B. Voslamber, H.P. van der Jeugd & K. Koffijberg

In the past decades, breeding goose populations have experienced a marked expansion throughout most of The Netherlands. By the 1970s, mainly Greylag geese were reported breeding (150 breeding pairs), along with few introduced Bar-headed geese and Greater Canada geese. A national survey of breeding geese in 2005 revealed nearly 40.000 breeding pairs of 13 different goose species. Meanwhile numbers have further increased (53.000 pairs in 2008). Greylag goose is still the most abundant species (35.000 breeding pairs), followed by Barnacle goose (8300), feral Greylag goose (3700-5000) and Greater Canada goose (4000). Apart from Greylag goose and Barnacle goose, which are considered native breeding species, all populations originate from introduction or escapes (e.g. live-decoy White-fronted geese that were released after hunting with live-decoys was prohibited in the 1980s). In most species, annual growth rate of the population has lowered after 1999. Exception is Greylag goose, that still experiences a mean annual increase rate of 19% and is now expanding especially in less densely populated areas e.g. in the northern part of The Netherlands. In areas where this species settled longer ago, population size has reached an equilibrium by a reduction in breeding success. The breeding birds are mixing with wintering and migratory geese outside the breeding season. At least for Barnacle goose, Greater Canada goose and Greylag goose exchange with populations abroad has been reported. Few Greylag geese migrate to wintering sites in Spain. In Barnacle goose exchange between the Dutch breeding population and breeding populations in the Baltic and NW-Russia has been reported. The expansion reported in so many goose breeding populations is part of a general increase in both breeding and migratory goose populations in NW-Europe. In The Netherlands, breeding has been enhanced by the numerous (partly newly established) suitable breeding areas that are intersected frequently with agricultural fields that provide optimal feeding conditions for breeding pairs and their goslings.

Enormous increase of wintering Anser anser in Saeftinghe

H.J.W.G Castelijns & C. Jacobusse

Greylag geese are invading the Verdronken Land van Saeftinghe, a brackish marsh in SW Netherlands. Before 1980 the Greyleg goose was rare in Saeftinghe; only e few hundreds of specimens were present during the autumn. They passed in October/November on their way to wintering areas in southern Europe (especially the south of Spain). Since 1980 there was an enormous increase of wintering Greyleg geese, which reached the top in 2003 with 77.000 birds. The increase reflects the development of the European population, but also in the area itself several factors can be determined that also caused the increase. Tranquillity and availability of food appear to be the most important factors within the area.

Grazing Anser anser determine the development of helophyte vegetation in Dutch wetlands

J.Th. Vulink, M. Tosserams, J. Daling, H.van Manen & M. Zijlstra

The population of Greylag geese that breed, moult and stay during winter in The Netherlands has increased rapidly over the last three decades. During moult Greylags stay in water and feed especially on leaves and stems of Common reed (Phragmites australis). During winter they feed on crops and on stolones and bulbs of helophyte vegetation. This helophyte vegetation protects the shore against erosion, filters nutrients and functions as spawning place for fish and breeding habitat for marsh birds. In the Oostvaardersplassen moulting Greylags are shown to have a key role in ecological functioning of the freshwater marsh system. By grazing they create diverse habitats that facilitates a high diversity in marsh bird species. On the other hand, grazing of wintering geese can prevent the development and expansion of helophyte vegetation completely as has been shown by the exclosure experiments on the shoreline of lakes in The Netherlands. We conclude that establishment and expansion of helophyte vegetation in large-scale wetlands can only occur through an optimal water level management. This water level management means a drawdown for several years followed by a water level of more than 0.5 m afterwards to protect the helophyte vegetation against heavy grazing by Greylag geese.

Effects of summer grazing by Greylag geese on the expansion of Reed

E.S. Bakker

The population of Greylag geese that breed in The Netherlands has increased rapidly over the last two decades. During moult Greylags stay on open water and graze on reed beds that expand from the shore into the water. These reed beds are of conservation interest as breeding habitat for marsh birds. In Lake Waterleidingplas in the centre of The Netherlands Greylags are shown to have a strong inhibiting effect on the expansion of water reed. Even though Reed regrows after the moulting geese have left, this regrowth results in reed stands with about half the amount of stems as in ungrazed stands and a much lower height. I conclude that grazing by Greylag geese can inhibit the expansion of Reed into open water.

Phosphate transport from agricultural land to oligotrophic lakes by geese

E. Brouwer & T.G.Y. van den Broek

Shallow softwater lakes occur on nutrient poor soils and are very susceptible to eutrophication. In the current landscape, waterfowl transport nutrients from eutrophied lakes and agricultural soils to those nutrient poor lakes. In particular the numbers of Greylag goose (Anser anser) and Canadian goose (Branta canadensis) are rapidly increasing. In this article, it is argued that densities of more then 2 geese/hectare/year lead to eutrophication and decline of characteristic vegetation of oligotrophic lakes within several years.

Do increasing Goose numbers affect farmland birds?

D. Kleijn & D. Bos

In The Netherlands geese numbers have been increasing rapidly over the past decades. Contrastingly meadow bird populations have been declining during the same period. Are these trends related, in the sense that geese affect meadow birds negatively? We studied some of the potential interactions between Lapwing (Vanellus vanellus) and Black-tailed godwit (Limosa l. limosa) with Barnacle geese (Branta leucopsis), that either winter or breed in The Netherlands. Aim of the study was to quantify to what extent goose grazing in spring affects the sward height of grassland and the activity patterns of breeding farmland birds.
The effect of grazing on sward height was studied using small exclosures. The activity patterns were quantified using direct observation in the presence and absence of geese.
Grazing by Barnacle geese in spring significantly reduced sward height. Breeding Lapwings and Godwits spent most of their time incubating. With geese nearby the proportion of time spent incubating by the waders was slightly but significantly higher than without geese. Geese and waders were rarely observed to interact in a direct way. In spite of the fact that we focused on a few particular situations where wintering Barnacle geese stayed until late spring or locally bred in large numbers, effects of geese on breeding waders appear to be limited. Further study should examine what effects geese have during the settlement stage and the chick rearing period.

Limiting Anser anser by measurements on eggs

B. Voslamber

In this paper is dealt with one of the measures which is undertaken to try to limit the populations of breeding geese: removing, addling and puncturing of eggs. Density-dependent regulation influences the effectiveness of measures greatly and particularly renders measures that affect reproduction ineffective. Removing, addling and puncturing of eggs have very little effect at the population level. This can be shown using population models and also followed from the evaluation of cases where egg removal had been applied for a number of years (fig. 1, 2). Similar conclusions were also drawn in evaluations of the large-scale removal of Black-headed gull eggs in the last decades. There is also concern about the possible effects on breeding success of vulnerable species that share the same habitat as geese.
Capturing and culling is more effective and it is easier to specifically target breeding birds then e.g. shooting. Unfortunately, effectiveness of capturing is limited in large populations as in the case of Greylag geese. Shooting is only effective when a very large and proportion of the population is shot annually. Moreover, shooting disturbs other species. All measures described hitherto are only effective as long as they are carried out. Stopping is equal to an almost straight return to the initial situation. Habitat management to make nesting and rearing habitat unsuitable for geese is potentially rewarding and sustainable. Studies in the Ooijpolder and De Deelen show that differently managed rearing areas vary greatly in survival and condition of growing young.
It is argued that beside ‘problems’ there are also benefits of large goose populations. They can help to manage nature reserves as they are doing in Oostvaardersplassen. Furthermore time will probably show that natural regulation will stabilize and maybe diminish the goose populations.

How does Dutch nature management relate to the strong increase of breeding geese?

B.W.A.F.H. van den Boom, B.F. van Tooren, E.H. de Hoop & T.G.Y. van den Broek

Over the last two decades nature management organizations were confronted with the strong increase of breeding geese. This development led to new and unknown problems, which evoked many questions. In 1994 Vereniging Natuurmonumenten defined a policy regarding the management of geese during the summer months. This policy states that serious damage to agricultural grasslands or nature values may give cause for the regulation of goose numbers. In case measures are proposed, small scale measures like egg-destruction and selective shooting have to be tried before large scale measures are taken. The removal of large groups of moulting geese can only be considered if all alternatives fail.

Based on the experiences of the last fifteen years, nature conservation organizations should now aim at a shared vision and a collective policy regarding geese management for the longer term. The crucial question is which position we grant breeding geese in the future. It is a question that, however difficult to answer, needs our urgent attention in order to sustain a durable position for geese within our Dutch landscape.