Lutra 47(1)_Bijlsma_2004

Long-term population trends of rabbits (Oryctolagus cuniculus) on Pleistocene sands in the central and northern Netherlands

As part of a large-scale study on the population dynamics of avian predators, major prey species, including rabbits (Oryctolagus cuniculus), were systematically monitored in two areas in the Netherlands, i.e the Veluwe (mainly Planken Wambuis, central Netherlands, 1974-2003: coniferous forest and heaths on sandy soil interspersed with some arable land) and Drenthe (Berkenheuvel, northern Netherlands, 1990-2003: coniferous forest and heaths on light-loamy sandy soil). Peak numbers were recorded in the late 1970s, probably a recovery from recurrent outbreaks of myxomatosis in the 1950s and 1960s. Severe winters, starting with the one in 1978/79, resulted in steep declines by 59-82%; the recovery afterwards never reached pre-crash levels. Consequently, the overall trend since 1979 was one of steady decline, with numbers in the 1990s being more than decimated compared with the 1970s (decrease of 95-99%). The reliability of this trend was validated by a similar trend in numbers shot at Planken Wambuis, and by the steeply declining proportion of rabbits in summer diets of goshawk (Accipiter gentilis) and buzzard (Buteo buteo) over the decades. It is suggested that habitat changes triggered the decline, following acidification and eutrophication of food-poor habitats on sandy soils (Deschampsia flexuosa became the dominant undergrowth in pine forests and on heaths), conversion of farmland into fallow land and - on the Veluwe only - a negative impact of rooting wild boars (which tripled in numbers between 1987 and 2003) on the remaining feeding grounds of rabbits. This trend was aggravated by a series of severe winters, and reached its nadir following the advent of rabbit viral haemorrhagic disease (RVHD) in the 1990s (although clinical proof is only circumstantial). RVHD probably wiped out already depleted rabbit groups and decimated thriving populations, with a serious impact on vegetation dynamics and the food base of avian predators (mainly buzzard and goshawk).