Friday, 3 April 2015

Fiddler Crab Predators

A lot of people have been looking at the “who eats fiddler crabs” post and I was starting to wonder if they had gone on the Paleo Diet.  When I wrote the first post, I was not sure which of our large birds had been dining on fiddler crabs but now I have collected more evidence.  Today on a small mud bank 10 m across, I found 4 detached nippers and bird footprints.  I would say a Beach Curlew (Esacus magnirostris) has been at work.
Uca dussumieri claws
The fiddler crab claws broken off by the bird - collected by me
There are more than a dozen large to very large birds in my area and some smaller ones with strong beaks, so working out who eats crabs is quite hard.  They very rarely eat crabs whilst you are watching and Beach Curlews are notoriously shy.  However I did see one giving something a really hard time one day and went to investigate.  I found the remains of a large sentinel crab.
Sentinel crabs probably put up a struggle and would be a bit bony to swallow, so the bird processes the crabs first and removes most of the hard bits.  It is more common to find the scene of the carnage than see it happening.

Esacus magnirostris, Beach Curlew eating a crab
Beach Curlew working on the shell of a sentinel crab
Sentinel crab remains
The actual crab shell from the Curlew's mouth
Scene of brutality against a crab, see the legs and shell.

Finally, I came across some Beach Curlew poo on a disused road that runs through the mangroves.  The curlews sleep there.  It is clear that crabs are a major dietary item.  When they eat soldier crabs it looks like the road runner in real life as they run the crabs down.  I don’t know how they catch sentinel and fiddler crabs as these crabs are fast and are always near a burrow.  Stealth is the more likely approach and I have seen Beach Curlews on the mud bank but they just stand there like they are waiting for the tide to go out.  They didn’t seem to be in attack mode.

Beach Curlew poo, mostly crab shell
On another web page someone said Whimbrels eat fiddler crabs.  Whilst this is possible and a Whimbrel was feeding near the mud bank, I would want to see more evidence before adding Whimbrels to the list.
Mouth of Richters Creek, Cairns - sort of place where birds catch fiddler and sentinel crabs
Uca dussumieri fiddler crab - the biggest of east Australia's fiddlers
Sentinel crabs in numbers on the sloppy mud.

No comments:

Post a Comment