Aarhus University Seal / Aarhus Universitets segl

No. 248: Mapping of habitats with proposed target and state assessment for staging waterbirds

Clausen, P., Therkildsen, O.R., Nielsen, R.D. & Holm, T.E. 2017. Kortlægning af levesteder med forslag til målsætning og tilstandsvurdering for rastende vandfuglefuglearter. Arter tilknyttet bundvegetation, enge og moser. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 120 s. - Videnskabelig rapport fra DCE - Nationalt Center for Miljø og Energi nr. 248.  http://dce2.au.dk/pub/SR248.pdf 

Summary 

This report presents the methods used for assessing the conservation status of Special Protection Areas for Birds (SPAs) designated under the EU Birds Directive, which have been further developed to assess the status of habitats available to staging waterbirds, associated with submerged aquatic vegetation, meadows and other wetland types in Denmark. The background for the work is described in the introductory chapter. 

Chapter 2 describes the situation for wigeon Anas penelope: explaining the basis for SPA designation, monitoring mechanisms in place, changes in abundance and phenology as well as the species’ behavioral, habitat and nutritional ecology. The effects of human disturbance, especially from hunting, on bird distribution and abundance and the positive effect of reserve designation on the distribution and number of birds are also described. The methods used to map key wigeon habitats and for calculating the size of the habitat required to support a given number of birds and total birddays are also explained. The wigeon is a specialist herbivore which primarily feeds on submerged macrophytes, but will also resort to grazing short graminoid swards, especially flooded wet grasslands. It is concluded that habitat mapping and calculation of food requirements for wigeon needs to take into account all herbivorous species, since these largely subsist from the same plants and thus are potential competitors for the same food resources. 

Chapter 3 describes the corresponding conditions for teal Anas crecca, which mainly subsist on seeds and small invertebrates, which they derive from submerged and emergent plans, on saltmarshes or in shallow wetlands. 

Chapter 4 of the report presents habitat mapping of the 12 Danish SPAs designated for wigeon and/or teal (three of which are located in the Wadden Sea and are described collectively). Since all these SPAs are designated for one or more other species associated with the bottom vegetation, habitat mapping also includes habitats exploited by mute and whooper swans, brent geese, other dabbling duck species and coots, in all encompassing a total of 54 species/SPA designations in the 12 sites. For each SPA, the species for which the site is designated is described (i.e. all species feeding on the bottom vegetation), the nature of its bottom vegetation and a habitat map of the wet grassland, meadows, lakes and wetlands within the SPA are described. The accounts provide a description of the contemporary SPA reserve management and proposals for target numbers of herbivorous waterbirds, based on the estimated food requirements for submerged vegetation, supplemented by grazing opportunities. 

Chapter 5 describes a proposal for a means of assessing the abundance and quality of the submerged vegetation in the shallow areas that the birds use to feed. It is argued that three key parameters should be included in this, namely the extent and percentage cover of aquatic plants in the depth range 0-1 metre in fjords, lagoons and lakes. The third is a parameter that describes the degree of overlap between the distribution of bottom plants and any reserves designated within the SPA. As with other methods for assessing the state of natural protected areas, the habitat assessment uses a scale that has values ​​between 0 and 1, where 1 represents the best state and 0 is the worst. 

The proposed methodology is then tested on two sites, Tippergrunden in Ringkøbing Fjord and Nibe-Gjøl Bredning in Limfjorden. These are located in two SPAs from which we know that there have been periods of documented widespread and abundant bottom vegetation, where many birds have been observed using the area intensively, confirming the high potential carrying capacity of these areas.  However, there have also been periods when the prevalence of bottom vegetation was considerably reduced, when consequently fewer birds occurred due to reduced local carrying capacity.  

For Tippergrunden, the preliminary condition assessment results gave a score of 0.91 in 1995 in a year where the status on the site was considered close to the best state (scored as High status, the highest level in a five-level scale equivalent to the environmental status scores under the EU Water Framework Directive), 0.30 in 1999 when submerged vegetation was restricted (scored as Poor status, or second-lowest level on the scale), and 0.83 in 2014 when conditions again improved (High status). For Nibe-Gjøl Bredning, the method returned scores of 0.84 in 1993 (High status, best level on scale); 0.41 in 2001 (Moderate status, mid-level on scale) and 0.75 in 2014 (Good status, second-best level on scale). 

Subsequently, preliminary assessments of the status of waterbird species dependent on submerged vegetation in the other areas was calculated based on the latest vegetation data available to DCE.  Unfortunately, such data on submerged macrophytes is typically several years old (from 1995-2000), because such mapping has not been undertaken in recent years. 

Including the results of the studies from Tippergrunden and Nibe-Gjøl, the preliminary status assessment exercise found three sites were classified as High status, four as Good status, one as Moderate status (the overall Wadden Sea area) and one as Low status. None were classified as Poor status, the worst on class the five-level scale.  For one remaining area, it was not possible to complete an assessment because of insufficient data. 

In the Wadden Sea, far greater numbers of grazing birds were present than could be explained by the available submerged vegetation food resource, despite following internationally recognized and standardized methods. This may be because (i) larger numbers waterbirds resting in the southern Danish Wadden Sea at high tide feed at low tide in the northern part of the German Wadden Sea and/or (ii) because a large proportion of these birds supplement their feeding on the saltmarshes or wetlands inland. 

Chapter 5 concludes with a section proposing a strategy and a priority for data collection and status assessments for the remaining 58 designations for aquatic herbivorous waterbirds in 31 other SPAs. 

Chapter 6 presents a proposal for a conservation status assessment system for the alternate habitats used by the two test species (wigeon and teal) in meadows and marshes (especially wetlands with clubrush Schoenoplectus and rushes Juncus). The proposed system is closely related to the currently implemented conservation assessment system for two breeding wader species, dunlin Caldris alpina and ruff C. pugnax, which are listed on Annex 1 of the Birds Directive. In addition to the standard assessment, this incorporates a parameter, which determines the degree of overlap between the extent of meadows and wetlands and the degree of coverage of reserves within the SPA. 

This method was then tested in two areas, East Vejler and Nibe-Gjøl Bredning in Limfjord, which generated a score of 0.92 (i.e. High status) for East Vejler in 2014 and 0.60 (Moderate status) for Nibe-Gjøl Bredning in 1998.