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Author Topic: Coconut Crabs  (Read 707 times)

Diane James

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Coconut Crabs
« on: November 10, 2017, 09:40:17 AM »

I came upon this https://www.sciencealert.com/coconut-crab-attacks-and-eats-seabird-red-footed-booby-gruesome article and video of a coconut crab killing and eating a seabird.  It gives me chills to imagine being Amelia or Fred, sick, hurt, and weak, being beset by a posse of these critters on the island.  Shudder!

--Diane
Diane James
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Ric Gillespie

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Re: Coconut Crabs
« Reply #1 on: November 10, 2017, 10:39:03 AM »

Thanks Diane.  The article contains some pretty stupid language ("innocent seabirds," "disturbing," "way, way worse than we could ever imagine," "crazy," monster crabs"). Laidre's paper at http://onlinelibrary.wiley.com/doi/10.1002/fee.1730/full is more useful and gives us some new information about Birgus latro.  We've known that coconut crabs, like all crabs, are scavengers, but we've previously seen no proof that they are also predators. I once saw a coconut crab on a tree branch dining on a dead rat, but there was no way to know whether he had found a dead rat or killed it himself. 

In the time lapse video of our pig experiment (https://youtu.be/uBXpSSEcXYs) most of the action is by the small, baseball-sized, strawberry hermit crabs.  The coconut crabs who show up are fairly small and they don't go off with bones.  For whatever reason, none of the big coconut crabs participated in the feast.  According to Laidre, "Five more coconut crabs came to the site within 20 minutes, likely cueing in on the blood with their neurologically acute olfactory sense (Stensmyr et al. 2005). The attacker responded by dragging the booby several meters away, and then released its grip. As the booby lay paralyzed, the crabs fought, eventually tearing the bird apart over several hours, carrying it away, and consuming it."  We've never seen coconut crabs carry pieces away.

The article says, " A daytime attack had been witnessed 2 years before by M Luchmun (pers comm). An adult red-footed booby had landed near the entrance to a coconut crab's burrow. As the bird stood there, the crab slowly emerged from its underground lair, approaching the bird from behind. The crab then grabbed the bird by one leg and dragged it, struggling, back into its burrow. The bird never remerged."  We've never seen a coconut crab drag anything into its burrow.

Also, "At present, the patterns in bird nesting behavior, together with the observations of predation by coconut crabs on one of the largest bird species on Chagos, raise an intriguing hypothesis for future testing: coconut crabs could act as “ruler of the atoll” for terrestrial communities, inducing fear, particularly in vulnerable, ground-nesting species. "  That is certainly not the case on Niku.  There are lots of coconut crabs but the boobies do nest on the ground.

I'll try to get in touch with Mark Laidre.  He might appreciate our experiences with Birgus latro and he may have some insights that will be useful in our research.
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Diane James

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Re: Coconut Crabs
« Reply #2 on: November 13, 2017, 05:33:14 PM »

Diane James
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Ric Gillespie

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Re: Coconut Crabs
« Reply #3 on: November 13, 2017, 06:56:48 PM »

Mark Laidre is eager to compare notes with us about coconut crabs. We have a conference Skype call scheduled for later this month.
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