Placental scar counts in the Red fox (Vulpes vulpes L.) revisited

Placental scars used for analyses of reproduction in the red fox (Vulpes vulpes L.) may fade throughout the season after birth. I report a method to calculate whelping frequency and mean litter size from placental scar analyses of 608 vixens shot during autumn and winter in three areas of Sweden. The material allowed 6-9 consecutive periods of calculation within the year in each area. By successively including scars of lighter shades in the counts, I established isopleths of constant whelping frequencies. The isopleth yielding the best estimate of mean litter size as derived from analyses of vixens in late pregnancy was accepted for calculations in each area. Although this method appeared to be adequate for each area, there were inter area differences