This is scientific Americans 60 Second Science. I'm Jason Goldman. Got a minute?

Small tasty mammals like dwarf mongooses have one main goal. Do not get eaten. So the animal, a type of

weasel, has a surveillance system. While most of the group focuses on finding

food, a handful of others watch for predators.

They take turns so that the burden is distributed equally.

But in other ways there's a definite class distinction.

You have a kind of typical cooperative breeding society which you see in a number of different

species like meekats for example or all African wild dogs so you have a dominant breeding pair, male and female

pair that will reproduce and they're the only group members then that are

guaranteed to have offspring. University of Bristol biologist Julie Kern.

But then within both sexes there's a linear dominance hierarchy.

So if you are quite far down the hierarchy in your own group, then it could take quite a long time for you to reach

that breeding position, which is what you really want. So it may be best for you to actually

leave your group that you were born into and try and join another group where there are a fewer same-sex

individuals so you can effectively join a group higher up the queue than the one that you're already in.

When new immigrants show up, that means more mongooses can act as lookout against predators, right?

In reality, it's more complicated. Kern and her team observed seven different groups of wild dwarf mongooses in South Africa.

They found that new immigrants rarely served as sentinels.

It wasn't until they'd been in their groups for five months on average

that they spent as much time working as lookout as the other mongooses did. The study was published in the journal

Current Biology.

Current thinks that the mongooses go through a transition phase

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