Declining survival rates of red foxes Vulpes vulpes during the first outbreak of sarcoptic mange in Sweden

Abstract

Rapid declines in red fox Vulpes vulpes populations have followed outbreaks of epizootic mange caused by the mite Sarcoptes scabiei. In Sweden, the first outbreak of sarcoptic mange started in 1977/1978 and affected the whole country by 1984. Here we used data on the number of harvested red foxes (51 480) from Gävleborg county (18 199 km 2 ) in Sweden between 1970 and 1994. We used data on the prevalence of sarcoptic mange in a sample of harvested red foxes (2694) from 1974 to 1982. A rapid decline in harvested foxes occurred two to three years after the prevalence of sarcoptic mange first became evident. In the same period, mark-recovery data were used to estimate changes in survival rates, and the best model included an effect of age (young or adult) and period (annual) on the survival and recapture probabilities. The analysis was based on data from 701 young foxes of which 523 were recovered, and 133 adults of which 131 were recovered. Average annual survival was 0.55 (range = 0.53-0.58) for adults and 0.36 (range = 0.32-0.39) for young foxes in the three years preceding the outbreak. During the outbreak and the remaining six years of the study, the average survival was reduced to 0.41 (range = 0.30-0.48) for adults and to 0.25 (range = 0.17-0.30) for young foxes. A population model, based on results on our survival analysis and literature data on fecundity, was developed to project the decline of the fox population. The rate and magnitude of the reduction in projected population and harvested foxes were similar, with both reduced by almost ninety percent. Harvest statistics indicate the fox population recovered to pre-mange densities in less than 10 years after the first detection of mange indicating a rapid development of resistance in the host. This study shows the importance of long-term population monitoring in combination with largescale field-experiments to devise alternative management options.

Density independent decline from an environmentally transmitted parasite

“…Like the present study, a host range reduction was also documented [ 7 ], and very low numbers of wombats continue to occur there [ 23 ]. Host population declines associated with S. scabiei are widespread in affected mammals, such as red-fox [ 30 – 32 ], kit fox [ 33 ], vicuña [ 34 , 35 ], ibex [ 36 , 37 ], chamois [ 38 ], grey wolf [ 11 ] and coyote [ 15 ]. Importantly, this research is the first to test for the effect of density in mange epizootics where transmission is principally environmental [ 9 ].…”

Assessing Variation in the Individual-Level Impacts of a Multihost Pathogen

“…A notable aspect of the literature in this study is the occurrence of research themes in pathogen impacts assessed among host species, especially for well-studied host species. For example, red foxes were commonly used to assess population and community-level efects of infection [60][61][62]. In contrast, studies on bare-nosed wombats, Iberian ibexes, and Japanese raccoon dogs were often used to assess the immunological and physiological efects given infection [38,[63][64][65][66][67][68][69], whereas coyotes and grey wolves were more frequently used to assess the behavioural and social efects of infection [70][71][72][73].…”

“…severe on average as some other host species, yet it has received the most attention within the literature. Te red fox has experienced occasional marked population declines throughout much of its range due to sarcoptic mange, with the disease persisting in relatively high prevalence [62,88]. 27) plotted against the average impact score (AIS) for S. scabiei impacts, with conservative criteria applied and the average range of AIS also shown.…”

Research, publications and knowledge in wildlife research and management

“…Predicting outcomes under uncertainty is one thing, predictions without understanding uncertainty can result in unexpected surprises (Allen and Gunderson 2011, Seville et al 2015). For example, the effects of the sarcoptic mange on the fox population and many of its prey populations when it first entered Sweden came as a surprise (Lindström et al 1994, Willebrand et al 2021. I think we need more emphasize on explaining knowledge, uncertainty and surprise to stakeholders and students (Tobias and Everson 2002).…”