The Red Fox Vulpes vulpes as a Regulating Factor for Breeding
Shorebird Populations in Southern Sweden
PAUL E. JÖNSSON
Department of Animal Ecology, Ecology Building, University of Lund,
S-223 62 Lund, Sweden
Habitat loss, due to exploitation and/or altered management of wet meadows, has been the main reason for the decline of several shorebird species breeding in southern Sweden. However, some populations have continued to decrease in numbers even in reserves and other areas with unchanged and suitable breeding habitat. The "Southern" Dunlin (Calidris alpina schinzii) and the Kentish plover (Charadrius alexandrinus), two species that breed mainly on grazed coastal meadows, have been studied on a population level in southwest Scania since 1981. In 1981-86, the reproductive output in both species was found to be very low; on average 0.15 and 0.30 fledged young per adult, respectively. Although adult survival was high (0.83 and 0.85, respectively), the low breeding success could not compensate for the annual mortality, and subsequently both populations were decreasing.
Intense nest depredation was found to be the main cause of low reproductive success in the Dunlin. On average, 80% of the nests were depredated (n= 303) while the corresponding figure for the Kentish plover was 68% (n=75). The main predators were red foxes, hooded crows (Corvus corone), stouts (Mustela ermines), and wild mink (M. vison), but their relative roles in nest depredation are not known.
The Kentish plover is considered a critically endangered species in Sweden, with a total population of less than 30 birds. The only regular breeding site during the 1980s, Ängsnäset near Falsterbo, was frequently visited by several red foxes and significant nest losses were recorded in both plovers and other breeding shorebirds. In order to keep foxes out of the area, an electric fence was put up during the breeding season in 1986. Nest losses were significantly lower within the fenced area than outside the fence in both 1986 and 1987 (on average 35% compared to 90%, in all species). In 1987-90, nest depredation increased again due to the more frequent presence of mink and crows.
The importance of nest depredation by red foxes in the Dunlin have been revealed after an outbreak of mange (scabies) in the fox population in southwest Scania, in 1987. Nest losses due to predation was down to 21% in 1989 and 14% in 1990 (number controlled nests: 71 and 65, respectively) compared with about 60% in the same area in 1981-86. In one area, now virtually fox-free, hatching success increased from 0.34 young per adult in 1981-86 to 1.29 young per adult in 1989-90.
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