Male elephant seals are killing themselves off with sex.
The randy animals make love with up to 50 females during the mating season but are more likely to die younger than less sexually active peers.
The five-ton male seals have a greater chance of getting injured in fights with other males and don't eat for three months because they stay on land during breeding season.
The study revealed that dominant males typically survive for up to 10 years while females generally live for twice as long.
Dr. Kyle Lloyd, of Pretoria University in South Africa, said: "These breeding seasons are quite chaotic. The beaches are so busy and the males are working hard.
"They can only get food from the ocean. When they come on land [to breed] they're competing with other males for access to females.
"They need to have fat resources stored to be able to fight other males and survive on land without eating anything for weeks or months at a time."