A 16-year-old hedgehog named Thorvald has been posthumously crowned the world’s oldest scientifically confirmed European hedgehog.
Citizen scientists discovered Thorvald in Denmark during a project that aimed to monitor the imperiled species. Published this month in Animals, the findings reveal insights on hedgehogs’ mortality, life expectancy and inbreeding—and document Thorvald’s record-breaking age.
“I cried tears of joy that I was holding an individual that lived for 16 years. That’s really good news for conservation,” lead author Sophie Lund Rasmussen of the Wildlife Conservation Research Unit at Oxford University tells the Guardian’s Phoebe Weston. “All my colleagues were laughing at me because they thought I was being so emotional.”
The average hedgehog, faced with a plethora of threats, only lives for about two years, the research revealed. Native to Europe, the small mammals have declined significantly because of habitat loss, pesticides and predatory pets. Soil sealing, or covering the ground with impermeable material such as concrete, cuts hedgehogs off from finding important food sources like worms and slugs. Surveys in the last two decades have put their numbers at less than one million in the U.K.—a sharp drop from about 30 million in the 1950s, per the Natural History Museum in London.
“Based on the destruction of natural habitats by [human] activities, including soil sealing, we expect that the hedgehog population will reduce up to 50 percent in the span of a decade,” Carsten Schiller, who heads the German conservation group Pro Igel, told Deutsche Welle’s Julett Pineda and Carla Bleiker last year.
To get a clearer idea of how the animals are faring today, 300 volunteers collected data on almost 700 dead hedgehogs found throughout Denmark as part of The Danish Hedgehog Project from May to December 2016. Of those, the researchers determined 388 hedgehogs’ ages at death by counting growth lines on the mammals’ lower jawbones—a process similar to counting rings on trees. These growth lines form because hedgehogs hibernate over the winter, causing their calcium metabolism to slow and bone growth to reduce or stop completely, per a statement. Each line represents one hibernation.
Prior to Thorvald, the oldest recorded hedgehog had lived for nine years, but the citizen scientists also identified hedgehogs that had lived to 11 and 13, in addition to the 16-year-old record-breaker.
The data suggest that male hedgehogs tend to live longer than females, which is unusual in mammals, per the Guardian. The average male studied lived 2.1 years, and the females’ average age was 1.6. Though about a third of the animals died at or before the age of one, those that surpassed that milestone could live much longer and reproduce for several seasons, per a statement.
“This may be because individual hedgehogs gradually gain more experience as they grow older,” Rasmussen says in the statement. “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.”
Most of the animals examined—about 56 percent—were killed on roadways, while 22 percent died in rehab centers after being turned in by citizens. Another 22 percent died of natural causes in the wild, and a cause of death could not be identified for 0.5 percent.
Population declines have led to increased inbreeding in hedgehogs, Rasmussen says in a statement. But surprisingly, the new study discovered that inbreeding did not seem to affect the animals’ expected lifespan.
“This study is one of the first thorough investigations of the effect of inbreeding on longevity,” Rasmussen says in the statement. “Our research indicates that 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 groundbreaking discovery, and very positive news from a conservation perspective.”
Thorvald died in 2016 after being attacked by a dog. Rasmussen tells the Guardian she recommends keeping dogs on a leash or inside at night when hedgehogs are out. “It’s very sad that he lived for so long and then died after being attacked by a dog,” she tells the publication. But Thorvald was relatively healthy at his death, despite his advanced age, which indicates that the animals could possibly live for even longer, if given the right conditions.