Danish hedgehog breaks longevity record

The world's oldest known European Hedgehog has been identified in Denmark by a citizen science project.

The hedgehog lived for 16 years, some seven years longer than the previous record holder. The Danish Hedgehog Project also identified two other long-lived individuals of 13 and 11 years respectively.

Despite these long-lived individuals, the average age of European Hedgehogs identified by the project was only around two years. About a third (30%) of hedgehogs died at or before the age of one year.

European Hedgehog is one of our most beloved mammals but populations have declined dramatically in recent years. In the UK, studies indicate that urban populations have fallen by up to 30% and rural populations by at least 50% since the turn of the century. To combat this, researchers and conservationists have launched various projects to monitor hedgehog populations, to inform initiatives to protect hedgehogs in the wild.

During 2016, Danish citizens were asked to collect any dead hedgehogs they found for the Danish Hedgehog Project, a citizen science project led by Dr Sophie Lund Rasmussen (also known as 'Dr Hedgehog'). The aim was to better understand the state of the Danish hedgehog population by establishing how long hedgehogs typically lived for. More than 400 volunteers collected an astonishing 697 dead hedgehogs originating from all over Denmark, with a roughly 50/50 split from urban and rural areas.

European Hedgehog is declining in many parts of its native range (Chris Teague).

The researchers determined the age of the dead hedgehogs by counting growth lines in thin sections of the hedgehogs’ jawbones, a method similar to counting growth rings in trees. The results have been published as a paper in the journal Animals.

Interestingly, the study found that male hedgehogs generally lived longer than females (2.1 vs 1.6 years, or 24% longer), which is uncommon in mammals.

However, male hedgehogs were also more likely to be killed in traffic. This may be because males have larger ranges than females and likely move over larger areas, bringing them into more frequent contact with roads.

Indeed, the research found that most (56%) of hedgehogs had been killed when crossing roads. Some 22% died at a hedgehog rehabilitation centre (for instance, following a dog attack) and 22% died of natural causes in the wild.

Dr Rasmussen said: "Although we saw a high proportion of individuals dying at the age of one year, our data also showed that if the individuals survived this life stage, they could potentially live to become 16 years old and produce offspring for several years. This may be because individual hedgehogs gradually gain more experience as they grow older. If they manage to survive to reach the age of two years or more, they would have likely learned to avoid dangers such as cars and predators."

Previous studies have found that the genetic diversity of the Danish hedgehog population is low, indicating high degrees of inbreeding. This can reduce the fitness of a population by allowing hereditary, and potentially lethal, health conditions to be passed on between generations. Surprisingly, the results showed that inbreeding did not seem to reduce the expected lifespan of the hedgehogs.

Dr Rasmussen concluded: "The various findings of this study have improved our understanding of the basic life history of hedgehogs, and will hopefully improve the conservation management for this beloved and declining species."