A 16-year-old European hedgehog named Thorvald is the world’s oldest, beating the previous record by seven years.
The male hedgehog lived near the town of Silkeborg in central Denmark. Dr Sophie Lund Rasmussen, from Oxford University, who led the Danish Hedgehog Project that found Thorvald, said she was overwhelmed when she found out how old he was.
“I cried tears of joy that I had someone I lived with for 16 years. That’s good news for conservation. Under the right conditions, hedgehogs can live for 16 years – it’s amazing. All my colleagues were laughing at me because they thought I was so emotional,” she said. The previous record holder in Ireland was thought to be a nine-year-old female hedgehog, who was identified by researchers in 2014.
Unfortunately, Thorvald died at the Danish Animal Protection wildlife rehabilitation center in Silkeborg in 2016 after being bitten by a dog, a common cause of hedgehog mortality. Rasmussen says dogs should be kept on leashes or locked up at night when hedgehogs are out. “It’s very sad that he lived this long and died after a dog attack.”
Thorvald was one of nearly 700 dead hedgehogs collected by 400 volunteers as part of the citizen science research. They also found a 13-year-old and an 11-year-old, according to the paper, published in the journal Animals.
The bodies were sent to researchers who worked out their age by counting the growth lines in their jawbones, like counting tree rings. This research is significant because hedgehog numbers are declining across many European countries, losing them due to habitat destruction, agricultural intensification, road traffic incidents and population fragmentation. In the UK, the rural population has fallen by as much as 75% in some regions in just 20 years.
Thorvald had infected bite wounds on his stomach and back; infection also caused it to be very swollen. “It was the biggest hedgehog penis I’ve ever seen,” said Rasmussen, who said the hedgehog was otherwise generally healthy – indicating the mammals can live longer than 16 years.
However, the average age of the animals studied was two, and a third of hedgehogs died before the age of one. Researchers believe that if hedgehogs can get past the difficult first years, they could live long lives and produce offspring for several breeding seasons. “This may be because individual hedgehogs gradually gain more experience as they get older,” Rasmussen said. “If they manage to live to reach the age of two or more, they would probably learn to avoid dangers such as cars and predators.”
They found that male hedgehogs lived longer than females – reaching an average of 2.1 years, compared to 1.6 years – which is unusual for mammals. Rasmussen said: “It’s probably easier to be a male hedgehog than a female. Hedgehogs are not territorial, which means that the males rarely fight. And the females raise their offspring alone.”
More than half were killed while crossing roads, with deaths peaking in July when males and females walk long distances trying to find others. Another 22% died at rehabilitation centers after being collected by the public and 22% of natural causes in the wild.
Jaw bone growth lines are an effective way to age hedgehogs as their metabolism slows down in winter and bone growth slows down or stops altogether. One line equals one year.
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Another key finding from the paper was that inbreeding did not appear to reduce their life expectancy. Finding an unrelated mate is an increasing problem for hedgehogs as populations decline.
Rasmussen said: “Our research shows that if the hedgehogs survive into adulthood, despite the high level of inbreeding that can cause some potentially fatal hereditary conditions, the breeding their longevity. That is a brand new discovery, and very positive news from a conservation point of view.”