Population variables and causes of mortality in a hedgehog (Erinaceous europaeus) population in southern Sweden

A hedgehog population in southern Sweden was studied by capture-mark-recapture during 1972–1979. Each animal was weighed, sexed and marked with one numbered clip in each ear.
The number of subadult and adult hedgehogs was about 20 in the first two years, 1972–1973. Numbers then increased and approximately doubled and the population peaked in 1978. A decrease came in 1979.
The estimated number of juveniles produced varied between years with the lowest figure (15 juv.) in 1974 when the population was low and the highest in 1977 (39 juv.) when the population was high. As no captured subadult female had suckled young, estimates of recruitment rate assumed that females did not reproduce until they were adult. The average number of juveniles per adult female was 2.8. Recruitment rate did not show any correlation with non-juvenile population densities.
For both juveniles and non-juveniles the annual mortality varied greatly between years. Average yearly mortality was 47% for non-juveniles and 34% for juveniles.
For non-juveniles, most of the total mortality occurred during winter, ranging between 26% and 43% (average 33%), and increased with increasing densities of non juveniles. Juvenile winter mortality varied between 6% and 94%, averaging 33%.
Summer mortality of non-juveniles averaged 15%, ranging between 3% and 22%. Traffic kills were the predominant cause of death. Only a few juveniles were found dead during summer and autumn.
There were no statistical differences in age-specific survival rate between males and females and, generally, no differences in survival rate between the age categories within each sex. It is argued that the population size appears to be more influenced by environmental factors, such as food availability, winter nest sites and winter climate, than by density-dependent factors.