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Zomerganzen - Summering geese management and population counts in Flanders, Belgium
Devisscher S, Adriaens T, Brosens D, Huysentruyt F, Driessens G, Desmet P (2021): Zomerganzen - Summering geese management and population counts in Flanders, Belgium. v1.6. Research Institute for Nature and Forest (INBO). Dataset/Samplingevent.

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Availability: CC0 To the extent possible under law, the person who associated CC0 with this dataset has waived all copyright and related or neighboring rights to this dataset.

Zomerganzen - Summering geese management and population counts in Flanders, Belgium is a sampling event dataset published by the Research Institute for Nature and Forest (INBO). The dataset contains over 3,700 sampling events, carried out since 2009, mostly in the months June and July. The data are compiled from different summering geese related projects, but most data were collected through fieldwork within the framework of the EU co-funded Interreg projects INVEXO ( and RINSE ( Since 2015, data collection is funded by INBO. The dataset includes close to 5,000 presence occurrences, as well as over 15,000 absence occurrences. more

The sampling protocol for the majority of the occurrences are simultaneous counts. Here, the number of individuals of different geese species in a fixed set of areas is determined. Counts are performed within the same weekend to avoid double counting. Simultaneous counts were organised yearly since 2008 and take place the first weekend after July 15, the best period for monitoring the summering population of geese. These counts are performed by professional INBO employees as well as experienced birdwatchers from Natuurpunt using a standardized field protocol. Data are recorded in a citizen science portal ( However, The dataset also comprises opportunistic field observations from the same portal outside this period. Furthermore, data are derived from management actions, such as fertility reduction (egg shaking and pricking), the use of Larsen traps (for Egyptian goose), and the execution of moult captures. Here, the individuals in the dataset were actually removed from the environment. The aim of the data collection is management follow-up and evaluation. Consequently, caution is advised when using these data for trend analysis, distribution range calculation, niche modeling or other.
Geographic coverage: In the initial stages, data from the simultaneous counts of summering geese were gathered at the level of the two westernmost provinces in Flanders (West Flanders, East Flanders), as these were considered in the Invexo and RINSE project's area. These are provincies with high numbers of summering geese, with several species under management (greater Canada goose, Egyptian goose, greylag goose). Here, a set of counting areas with confirmed presence of geese was selected and maintained as the sample study area over the years. Since 2014, management has been upscaled to other provinces. Therefore, counts are organised at the level of the whole Flanders region since.
Taxonomic coverage: All 20 species (and some subspecies and hybrids) in this dataset belong to the waterfowl family Anatidae. More than 80% of the occurrences are swans and true geese (subfamily Anserinae). Some individuals were not identified to species (e.g. unknown hybrids, eggs).
Sampling methods: This dataset contains data from several types of goose management as well as monitoring data. Management is performed with one of several methods: - Moult captures: during the moulting period (June-July), when the geese tend to congregate on open water, geese are trapped in large numbers with corral traps. - Larsson trap captures: for Egyptian goose (Alopochen aegyptiacus). The data are from a floating Larsson-like trap using a live decoy bird. Traps are checked daily for any caught specimens and bycatch. - Fertility reduction: the eggs are mostly pricked with a nail so the animal remains on the nest, sometimes eggs are shaken to destroy the embryo. Monitoring is performed using the following census method: - Simultaneous counts in summer (1st weekend after 15 July, a date which is set in accordance with the regions surrounding Flanders): multiple volunteers from bird working groups (Natuurpunt vzw) perform simultaneous count (within the same weekend) of a list of the more important goose sites (west and east flanders 2009-2013, Flanders since 2014). Counts are coordinated by the ngo Natuurpunt and a citizen science portal ( is used for standardized data input and feedback to volunteers. Only when a site was completely surveyed for all of these species the observation was given the "Simultaneous count" - sample type. - Counts of geese at moulting sites (June 2012): during one day 8 teams of specialists visited every pond in the province of West-Flanders with a surface area of 5 hectares or more in search of groups of moulting geese. Also big streams where inventoried. - Field observations: These contain occurrences from 2 different sources: (1) counts carried out 3 days prior to or after the simultaneous counts weekend within the borders of any of the sites of intrest. These aren't necessarily completely surveyed for all species and should therefore be treated as loose, opportunistic observations, and (2) counts carried out during the simultaneous counts weekend within the borders of any of the sites of intrest but incompletely surveyed for all the species.
Study extent: Flanders. Scope: management evaluation based on management results reporting and standardized monitoring census data. Species: greylag goose, feral domesticated goose, barnacle goose, Egyptian goose, greater Canada goose, other non-native goose species (bar-headed goose, Magellan goose).
Quality Control: The fieldwork is performed by skilled volunteer birdwatchers, often working together within local bird clubs. The NGO Natuurpunt supports the majority of these bird clubs and volunteers, and thereby delivers an important contribution to the project. Quality control on the data was performed by Natuurpunt Studie vzw. Additionally, all the data was validated by experts from the Research Institute for Nature and Forest (INBO).
Purpose: Impact scoring for established non-native birds in Europe has shown Canada goose (Branta canadensis) to have the highest environmental, economic (agricultural damage) and social impact of all non-native birds species. Among the ecological effects are overgrazing, fouling, trampling of vegetation such as reed beds and meadows, bioturbiation of oligitrophic fens and pathogen transmission. Also, geese cause agricultural damage and nuisance in recreational areas. Management of invasive geese in the region (western Flanders, eastern Flanders, Zeeuws-Vlaanderen) was, until recently, mainly done by egg pricking and hunting. Within the framework of the EU co-funded Interreg projects Invexo and RINSE, the coordination of egg pricking and hunting was enhanced and additional moult captures (n=131) were performed on a larger cross-border scale. Moult captures were very successful for Canada geese, with a total of 7829 caught between 2010 and 2013. Greylag geese (Anser anser), although comparable in density, tended to move away from catching sites during the moulting season. In relation to density, catch success for feral goose (Anser anser f. domestica) was high. Barnacle geese (Branta leucopsis) moult later and were therefore only caught in very low numbers. The reported numbers of Canada geese culled by hunters also increased in the same period with over 7000 birds shot per season. The overall impact of the combined management efforts was assessed by annual simultaneous counts of the geese populations in the region using a fixed sample of counting areas. Trends in the average number of geese per municipality and per year were modelled using gee-GLMs. This showed a significant decrease in the number of Canada and feral goose since the beginning of the projects. In East Flanders, where moult captures were applied most intensively, a significant yearly decrease was noted. Here, the modeled decline was in line with the trend in the absolute numbers of Canada geese which showed a 40 % reduction since 2010. For the species caught in high numbers, the impact was significant over four years, and related to catch effort. Although suggesting a link between moult captures and population numbers this approach would assume other management efforts to be evenly applied over the project area, which was not the case. Moreover, the absolute number of geese in the entire area hardly decreased in the last year. Recent research indicates that Canada geese disperse over large distances within Europe, blurring effects of a local action over the years. Goose captures were performed within the EU co-funded Interreg Invexo (2010-2012) and the Interreg 2Seas project RINSE (2012-2014), which seeks to improve awareness of the threats posed by INNS, and the methods to address them. Future work will be to upscale management and implement adaptive management backed by population models and thorough monitoring. This requires continued investment in prevention, awareness raising and generating public support.
Issues with the dataset can be reported at
The publication of this dataset was supported by the INBO as part of the Flemish contribution to LifeWatch.

Biology > Birds
Terrestrial, Belgium, Flanders, Anatidae Vigors, 1825, Aves

Geographical coverage
Belgium, Flanders [Marine Regions]

Temporal coverage
From 22 June 2010 on [In Progress]

Taxonomic coverage
Anatidae Vigors, 1825 [WoRMS]
Aves [WoRMS]

Occurrence of biota

Natuurpunt, moredata creator
Vlaamse overheid; Beleidsdomein Omgeving; Instituut voor Natuur- en Bosonderzoek (INBO), moredata creator

LifeWatch: Flemish contribution to, more

Dataset status: In Progress
Data type: Data
Data origin: Data collection
Metadatarecord created: 2017-06-26
Information last updated: 2021-07-14
All data in the Integrated Marine Information System (IMIS) is subject to the VLIZ privacy policy