Thorup, O., Clausen. P. & Bregnballe, T. 2021. Ynglefugle i Vadehavet 1996-2018. Status for 2018 og bestandsudvikling for udvalgte arter. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 90 s. - Teknisk rapport nr. 220. http://dce2.au.dk/pub/TR220.pdf
The abundance of breeding birds in the Danish Wadden Sea are surveyed in connection with monitoring under the trilateral monitoring programme (TMAP), which coordinates coverage of the entire international Wadden Sea, i.e. those areas of the Wadden Sea distributed between the Netherlands, Germany and Denmark. Monitoring of the distribution and abundance of breeding birds in the Wadden Sea is carried out under the Danish NOVANA programme. The TMAP breeding bird programme began in 1990, consists of a coordinated total count of a number of species of breeding birds considered characteristic of the Wadden Sea and a full survey is undertaken every six years. The objective of the programme is to track long-term changes in the numbers and distribution of selected species. The results are then available to provide a basis for implementing conservation management actions aimed to protect the species and their habitats in the Wadden Sea.
The latest census carried out in 2018 was the fifth total census, which repeated counts carried out in 1996, 2001, 2006 and 2012. For some species, data from 1991 are also included from a census carried out that included large parts of the Wadden Sea excluding mainland marsh areas.
In addition to these total counts, numbers of colonial-nesting coastal birds such as Pied Avocets Recurvirostra avosetta, terns and gulls are counted throughout the Wadden Sea every year, as well as annual counts of several of the Wadden Sea species of breeding birds, which are undertaken within 11 smaller control areas.
This report presents monitoring results relating to 35 bird species undertaken in 2018, with descriptions of changes in their distribution and abundance since 1996. While the species profiles for less common and irregular breeding species are brief, the treatment of the more numerous species is more extensive and illustrated with detailed figures and/or tables.
The concluding section compares numbers of breeding birds recorded in 2018 with those from 1996. During this period, 27 of the 35 species included in the breeding bird monitoring programme have had at least 10 breeding pairs in the Danish Wadden Sea.
Increasing species
One species, Eurasian Spoonbill Platalea leucorodia, has newly colonised the area.
Three species have more than doubled their numbers of breeding pairs during the period, i.e. the three large gull species Great Black-backed Gull Larus marinus, Herring Gull L. argentatus and Lesser Black-backed Gull L. fuscus.
Three of the species breeding successfully in 2018 did so in numbers that had increased by between 50% and 100% of the number of pairs recorded in 1996, namely Kentish Plover Charadrius alexandrinus, Ruff Calidris pugnax and Mediterranean Gull Ichthyaetus melanocephalus. In the case of the Ruff, however, overall percentage changes do not reflect precise changes in local breeding abundance, because the abundance of this species fluctuates greatly from year to year, and numbers of pairs settling to breed are highly affected by water levels and hydrology.
Species with (more or less) stable populations
Four species which bred in 2018 had numbers between 105% and 85% of the number of pairs recorded in 1996 (Shelduck Tadorna tadorna, Eurasian Curlew Numenius arquata, Redshank Tringa totanus and Black-headed Gull Chroicocephalus ridibundus), while two species bred with between 75% and 85% of the 1996 breeding numbers (Black-tailed Godwit Limosa limosa and Black Tern Chlidonias niger).
Declining species
Fourteen characteristic Wadden Sea breeding bird species were recorded as breeding in fewer numbers in 2018 (< 75%) than in 1996. Among these, breeding numbers of nine had fallen by more than half, whereas one species (the Gull-billed Tern Gelochelidon nilotica) no longer breeds. Waders and terns dominate the group of species showing declines, together with Common Eider Somateria mollissima, Common Gull Larus canus and Short-eared Owl Asio flammeus. The decline of two species may not have severe consequences for the population. This is the case for the Sandwich Tern Sterna sandvicensis, which does not breed annually in the Wadden Sea, as well as for the Short-eared Owl, whose local breeding abundance and distribution fluctuates greatly from year to year, in relation to the changes in abundance of its rodent food supply.
The report has not attempted to determine changes in relative abundance of eight rare or irregularly breeding species. The Cormorant Phalacrocorax carbo, Barnacle Goose Branta leucopsis, Pintail Anas acuta and Little Ringed Plover Charadrius dubius bred in very small numbers in 2018, while Red-breasted Merganser Mergus serrator, Wigeon Anas penelope, Hen Harrier Circus cyaneus and Turnstone Areneria interpres were not detected breeding in 2018.
The last section of the report compares the abundance of four breeding meadow bird species in Tøndermarsken's Ydre Koge in 2018 with targets previously set for the sizes of the populations, approved by the Danish Minister of the Environment, following their endorsement by the Tøndermarsken Advisory Board (Tønder Municipality). Lapwing Vanellus vanellus, Black-tailed Godwit and Redshank bred in numbers that failed to reach the minimum values established for species abundance in each case, so current management had failed to achieve these objectives by 2018.
