European Hedgehog Breeding Biology - Dispersal & Maturity
Despite having a reasonable understanding of how rescued and rehabilitated hedgehogs disperse from their release site, we know frustratingly little about the process within the family unit. Hoglets are typically independent at the point of having been weaned, at around 16 weeks old and a weight of some 250g (9 oz.). Interestingly, unlike most other mammal species, hedgehogs don’t appear to actively drive out their offspring, although we don't know what prompts the family to go their separate ways. My suspicion, based on a handful of tentative reports and observations, is that the mother simply gets up and vacates the nest one day, leaving the hoglets to their own devices. With mum missing-in-action, the hoglets, having already been exploring their environs for the last two or three weeks are forced out to find food. Once they have left the family fold, they do not appear to socialise with their mother or siblings and appear generally intolerant of company.
A genetic study published in Molecular Ecology in 1998 reported restricted gene flow between their sample populations in Oxford, indicating only occasional dispersal. Patrick Doncaster and his colleagues found disperal among their subjects to be patchy. Hedgehogs in their study population in Oxford did disperse, sometimes several kilometres, but had no obvious dispersal stage. Conversely, the west London studies of Pat Morris and Nigel Reeve suggest that young have a dispersal stage shortly after weaning and it is during these few months that they establish their future adult ranges (either before, or soon after, their first winter).
Doncaster and his co-workers also observed that some types of habitat (e.g. arable land) and landscape features (e.g. roads) are actively avoided by hedgehogs and may limit their potential to disperse. When dispersal does occur, tracking studies, including that by Doncaster and his team, suggest males and females disperse equal distances. A study by Hanne-Mari Saether at Trondheim University radio-tracked 25 juvenile hedgehogs in Trondheim (Norway) for four weeks and found no differences in dispersal distance, dispersal date or body weight at the time that could be related to sex. Adult males undergo a temporary range expansion or shift to search a larger area for females during the breeding season, but this is not true dispersal because they return to their core range at the end of the season.
There is debate as to the age at which the hoglets will become sexually mature. In Hedgehogs, Nigel Reeve suggests that, while captive individuals have been observed to reach maturity at only seven months old (perhaps owing to the ready supply of food), wild individuals are unlikely to become sexually active until between nine months and a year old. Consequently, most wild hogs will not breed during their first spring or summer.
In his 1971 paper to the Journal of Zoology, Pat Morris suggested that, based on his studies of epiphyseal fusion of the forelimb bones, hedgehogs may be fully grown by about 18 months old, while more tentative data from Chris Dickman’s paper to the same journal in 1988 proposed that, based on road casualties, the maximum size was reached at two or three years old. Working in Sweden, Han Kristiansson noted that female hedgehogs do not produce young until their third summer, when they’re about two years old. In her 1934 paper to the Philosophical Transactions of the Royal Society of London, Ruth Deanesley considered that animals born late in the year (i.e. August or September) might not be ready to breed until they’re about a year old, having reached a critical breeding weight; coming into oestrous in June, they may account for some of the pregnancies observed in the latter half of the breeding season.