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Zoologger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the world

Species:
Habitat: being rather lackadaisical in

If you believe the Manic Street Preachers, there is no true love – . Once we’ve decided that another person is our special someone, we can become dangerously possessive and murderously unwilling to share them with others.

Such all-consuming jealousy has a major downside: it’s just so much effort. What if you can’t be bothered?

That seems to be how Hoffmann’s two-toed sloths treat their sexual partners. Males do defend territories from rivals, but their slothful natures mean they aren’t much good at holding onto females.

Slow, so slow

All sloths have a reputation for being lazy. This is sometimes exaggerated – they don’t sleep much more than humans do – but basically correct. Sloths have unusually low metabolic rates and spend hours each day doing nothing.

is a case in point. It spends the day hanging upside-down from branches high in trees, often hidden away within tangles of vines. During the night the sloths move around and feed, often for 7 or even 11 hours. But they’re not exactly athletes, moving along branches at .

They are also completely and utterly antisocial. Unless they’re mating or caring for a youngster, you hardly ever see more than one sloth in a tree.

That suggests male sloths might be territorial, controlling patches of forest and preventing other males from entering. Controlling territory is one way of controlling access to females. But of the University of Wisconsin-Madison wondered how good these slothful males would be at monopolising females.

Every breath you take

With , Peery monitored 152 sloths in Costa Rica from 2010 to 2011. Most males had small home ranges of less than 0.2 square kilometres. There was some small overlap around the edges of the ranges but, in general, males kept out of each other’s territories.

That wasn’t true of the females though. On average there were 3.2 adult females within the range of each male, and 60 per cent of females lived in the ranges of more than one male – sometimes as many as four.

So it didn’t look like the males were monopolising the females, and that was confirmed by paternity tests. Females and their offspring were sometimes found living in the range of a male other than the father, so males aren’t controlling the females in their territories. Or if they are, the males haven’t really mastered the skill.

The slow-moving nature of sloths may be largely responsible for the males’ casual attitude, but Peery points out another possible explanation. Males tend to set up their territories close to their birthplace, often within a kilometre, so neighbouring males were often closely related.

As a result, males can actually benefit their genetic legacy by allowing neighbours to sneak in the odd mating. By doing so, they are helping relatives to pass on their genes – many of which they will share.

If that’s true, careless laziness is a way to help your family prosper.

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