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Bizarre Adaptations

The male fiddler crab looks like any other species of crab except for one rather obvious difference; one claw is substantially bigger than the other. The crabs use these oversized claws to attract females by raising them up and waving them around. The females choose which male they prefer based on how fast they wave and how big their claw is.

Research published recently by Richard Milner and his colleagues at The Australian National University investigated how fast male crabs waved when there were different numbers of other males around them. "We measured their wave rate by simply counting how many waves they produced over one minute. Competition was measured by counting how many neighbours were waving. Basically we showed that male courtship effort (wave rate) increases as competition increases. That is, males try harder when there are other males present," Milner explained.

The claw is an effective way for the male crabs to advertise themselves to the females, but waving uses up a lot of energy. By waving more slowly when there is less competition from other males, the fiddler crabs don’t use up waste energy unnecessarily.

About the scientist: Mr Richard Milner

What do you enjoy most about studying animals in their natural environments?

You get to conduct research in the field (not in the laboratory), which often involves exotic places like Zanzibar in Africa.

What do you enjoy about being a scientist?

You get paid to study things that you love and are passionate about. It definitely isn't your usual 9 to 5 job.

Why did you choose to study fiddler crabs?

They are highly social and display a broad range of complex behaviours that can be observed over relatively short periods of time. They are also a very charismatic and live in very exotic and wonderful locations (e.g. Africa and Northern Australia).