Thorvald, a 16-year European hedgehog that died in 2016, has been crowned as the oldest hedgehog in the world, breaking the previous record by seven years. On average, the animals, typically found in wooded areas, gardens and parks across Europe, the Middle East, Africa and Central Asia, live only for around two to three years, but Thorvald shows there’s so much we don’t know about them.

Populations of the European hedgehog have been declining fast in recent years. In the UK, for example, studies showed urban populations have dropped by 30% and rural populations by 50% since the turn of the century. To address this, researchers have launched several projects to monitor populations and protect hedgehogs in the wild and see what’s hurting them and what we can do to better protect them.

These include the Danish Hedgehog Project, a citizen science program led by Oxford University researchers. In 2016, scientists asked Danish citizens to collect any dead hedgehogs they found to better understand how long they live. Over 400 volunteers collected 697 dead animals from all over the country, including our friend Thorvald.

“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,” Sophie Lund Rasmussen, study author from Oxford University, said in a recent media statement.

A close look at hedgehogs

Rasmussen and her team established the age of the dead hedgehogs by counting growth lines in thin sections of the animals’ jawbones – just like counting growth rings in trees. Jawbones show growth lines because calcium metabolism slows when they hibernate in winter, causing bone growth to partially reduce or even completely stop.

The oldest hedgehog in the sample was 16 years old, seven years older than the previous record holder, who lived for nine years. Two other hedgehogs lived for 13 and 11 respectively. However, the median age was around two years. Most were killed when crossing roads, while the rest died of natural causes or at rehabilitation centers.

Male hedgehogs lived longer than females, the study showed, which is uncommon in mammals. Males were also more frequently killed in traffic, especially in rural areas and during July, which is the peak of the mating season for the month of July. They walk long distances and cross more roads during that time period, Rasmussen said.

The researchers also collected tissue samples to see whether inbreeding influenced how long European hedgehogs live for – with previous studies suggesting that the genetic diversity of the animals in Denmark is low. However, the results showed that inbreeding didn’t seem to reduce the expected lifespan of the beloved animals.

“If the hedgehogs manage to survive into adulthood, despite their high degree of inbreeding, which may cause several potentially lethal, hereditary conditions, the inbreeding does not reduce their longevity. That is a rather ground-breaking discovery, and very positive news from a conservation perspective,” Rasmussen said in a statement.

The study was published in the journal Animals.