These Aussie marsupials are having so much sex they are literally killing themselves

Death by sex may seem counterproductive to the survival of a species, but many animals have evolved the behavior to maximize reproduction.

(CNN) — They are small, mice-like critters known for their marathon mating sessions, which can last up to 14 hours. And that may be their undoing.

The Australian government has added two species of antechinus, the black-tailed dusky and the silver-headed, to its endangered species list, saying all that sex is killing them.

During mating season, which lasts for several weeks each year, males and females move frantically from one mate to another. There’s no courtship, just sex — with as many partners as possible.

To some dudes, this might sound like a dream. But it’s all so exhausting for the males that they typically die four or five days after the breeding season ends, according to Andrew Baker, head of a research team that has discovered five new species of antechinus since 2012.

Baker explains that while both males and females get stressed, only the males produce testosterone. The constant high levels of testosterone keep the stress hormone, cortisol, from shutting off. Eventually, it reaches toxic levels and causes the animal’s immune system to malfunction. The animal then bleeds internally and dies.

A species that purges half of its adult population every year is already in a vulnerable situation, but the antechinus also faces pressure from humans.

The antechinus likes structure: grassy areas and trees, explains Baker. As humans chop down trees, the furry marsupials are losing their habitat.

Antechinus are native to northern and eastern Australia and need a wet and cold climate. Not surprisingly, global warming is having an impact.

Baker says there could be as few as a few hundred animals of each of the two species left.

In order to protect them, Baker says, humans need to get the antechinus to migrate to southern Australia, where it’s colder. But researchers aren’t sure how to introduce them to those areas, he says.

To study the antechinus, Baker’s team uses detection dogs trained to sniff them out. One pooch found antechinus species in the Scenic Rim, an area that hadn’t seen the marsupial since the late 1980s, Baker says.

Baker’s team also uses metal box traps and collects fecal pellets to learn about the animals’ diet.

So what if researchers tried to keep males and females separated? Baker says the males would only make it if males and females were in total isolation and only if females were introduced one at a time.

In an experiment, castrated males did survive — but that doesn’t do much for reproduction.

Death by sex may seem counterproductive to the survival of a species, but many animals have evolved the behavior to maximize reproduction.

One example: garter snakes, who engage in massive, tangled orgies so exhausting the males age faster and die sooner. Happy googling.