Fiddler crabs build chimneys around their burrows to keep intruders out

Australian News.Net
Monday 13th October, 2008 (ANI)

Canberra, Oct 13 : A new study by Australian researchers has found out that fiddler crabs build chimneys around their burrows to keep intruders out.

According to a report by ABC News, a team at the Australian National University in Canberra has reported its findings on Uca capricornis, the technical name for the fiddler crab, in the journal Biology Letters.

Fiddler crabs live on tidal mudflats and lock themselves away in air-filled sealed burrows when the tide comes in, according to team member Rachel Slatyer, a behavioural ecology student, who carried out the research under the supervision of Dr Patricia Blackwell.

Blackwell said that a small percentage of these burrows are surrounded by mud mounds, or chimneys, and biologists have long wondered why this is so.

Slatyer and colleagues studied 70 crabs at a site in Darwin and tried to detect differences between those that build chimneys and those that don't, hoping the difference might shed light on the role of the chimneys.

They studied how much time crabs spent in and out of their burrows, how far they travelled from their burrows, and how much time they spent feeding or having aggressive interactions.

The only difference the researchers noticed was that those with chimneys didn't feed as much as those who didn't have chimneys.

The team hypothesized crabs that built chimneys didn't need to eat as much because they already had enough food - and thus enough energy to build chimneys.

"Other crabs appeared to not have enough food, and had to spend their time and energy looking for more food rather than building chimneys," said Slatyer.

Slatyer and colleagues then conducted an experiment to see what impact chimneys had on keeping intruders out of burrows.

Crabs generally try to defend their burrows, according to Slatyer, and if they find themselves taken away from their own burrows, they will attempt to hide in someone else's.

So, the researchers set up plastic arenas around burrows, some of which had chimneys and some of which didn't.

They put a foreign crab into the arena and then measured the time it took them to find the burrow.

"Most of the time, they didn't find the burrows with a chimney at all," said Slatyer. "It was quite surprising," she added.

The researchers conclude that it is possible that some crabs build chimneys to conceal the entrance of their burrows and reduce the risk of losing it to an intruder.

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