Aarhus University Seal / Aarhus Universitets segl

No. 160: Breeding birds in Tøndermarsken and Margaret Kog 1975-2015

Clausen, P., Hounisen, J.P., Asferg, T., Thorup, O., Nielsen, H.H. & Vissing, M.S. 2016. Ynglefugle i Tøndermarsken og Margrethe Kog 1975-2015. Evaluering af effekten af en intensiveret rævebekæmpelse og evidensbaserede anbefalinger til forvaltningstiltag. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 84 s. - Videnskabelig rapport fra DCE - Nationalt Center for Miljø og Energi nr. 160.



This report is the sixth in a series of reports from DCE (Danish Centre for Environment and Energy) published since 2003 investigating the factors affecting breeding bird abundance, distribution and breeding success at Tøndermarsken.

Results from studies conducted during the years 2002-2009, together with breeding bird (since 1975) and mammalian predator abundance (since the 1950s) monitoring data were fully discussed in a comprehensive report produced in 2010, which provided an “analysis of trends in the numbers and distributions with recommendations for management actions”. That report concluded that it was mainly a combination of intensified agriculture (associated with changes in cultivation and drainage) and high densities of mammalian predators and birds of prey in the 1990s and 2000s, which had led to significant declines, especially in the number of breeding wet meadow avian species and colonial nesting gulls, terns and avocets compared with the numbers present in the 1970s and 1980s.

One of the recommended management actions was to regulate fox abundance more effectively in order to increase avian reproductive success and ultimately enhance the size of breeding populations.

This report updates the recent size and status of breeding bird and fox populations in the area during 2010-2015 and assesses the success of attempts to reduce the fox population in the local area and, in so doing, improve avian breeding success.

The report shows that the status of breeding birds in the area generally has remained unchanged since 2009. This means that those species which failed to meet the threshold population targets set in the Environment Ministry's “Protection and use of the outer parts of Tøndermarsken 1999 Statement” in 2010, have still not reached these targets. These species comprise oystercatcher, lapwing, common snipe, black-tailed godwit, ruff, redshank, tufted duck and black tern. This report has also added shoveler to the list of species that failed to meet population size targets (whose status was rated as uncertain in the last report).  For mute swan, greylag goose, shelduck, mallard, teal, garganey and gadwall the threshold target levels were met within the present time period.

The report concludes that it has not been possible to reduce the fox population as a result of the implemented management actions.  The significant decline in fox numbers in the last year of the study and the improved breeding success of Lapwings in that year was considered unrelated to fox control, but due to an outbreak of paramyxovirus distemper that decimated the fox population not only at Tøndermarsken, but throughout South-West Jutland.

Chapter 5 of the report presents experiences from managing meadow birds at three other areas, (i) at Bygholm-meadows, Vejlerne in north Jutland, (ii) on the Tipperne peninsula, Ringkøbing Fjord and (iii) in the neighboring Rickelsbüller Koog in Germany.  Results from these areas show that targeted management of both water levels and grazing, even associated with high predator densities, can support much higher densities of breeding meadow birds than those currently occurring at Tøndermarsken. The report concludes with an updating of the recommendations from the 2010 progress report for the effective future management of breeding birds in the area. Here the authors retain that more targeted initiatives should be implemented that enhance conditions for the birds during the breeding season, if one wants to promote greater populations of breeding birds in Tøndermarskens Ydre Koge. It involves ensuring more moist areas which attract breeding birds and ensure their offspring a better food supply and higher growth rates. Ensuring later release and maximum densities of grazing cattles and horses, to reduce nest trampling. Ensuring more effective removal of lamb and sheep cadavers from the area, in order to remove primary food resource of the foxes in the area. Ensuring actions to reduce opportunities for raptors and corvids to breed in the area.

Furthermore, it should be considered to establish more realistic goals for breeding bird numbers in the area, because the current targets are based on a period of unnatural and significantly lower fox populations than exists today.