EN
Reproductive strategies of the raccoon dog Nyctereutes procyonaid.es (Gray, 1834) and the red fox Vulpes vulpes (Linnaeus, 1758) were studied in southern Finland in 1986-1995. Litter size and relative litter weight, body size, population status and ecology were compared. Although the body size is almost equal, diet rather similar and both raccoon dog and fox populations have been rather stable during the study period, the litter sizes and relative litter weights differ greatly. The mean litter size of the raccoon dog was 9.0 and that of the red fox 5.1. The mean relative litter weight was 18.3-24.0% for the raccoon dog and 10,4-12.5% for the red fox. Thus, raccoon dog females are able to invest relatively more in reproduction than the red fox. There are several features in the ecology and behaviour of these species which can explain the different strategies. First, vole cycles have a strong effect on red fox reproduction, but have only a week effect on the litter size of the raccoon dog. Second, the raccoon dog sleeps during harsh winters and females are in good condition in the breeding season regardless of the weather and food supply during the winter. The red fox is always active in winter when food availability may be low and moving in snow is energetically costly. Omnivory, the ability to accumulate large fat reserves and winter dormancy guarantee the good condition of raccoon dog females even in fluctuating environments by reducing the relative costs of reproduction. Third, raccoon dog pups are easy prey to other predators, and mortality during their first year is very high. If mortality rate before the reproductive age is high and independent of litter size, natural selection will favour large litters. Juvenile mortality among red foxes is lower, and it probably would increase in larger litters due to eg starvation.