Bird Watcher's General Store

Who Eats the Fiddler Crabs? - 11/04/05

Dear Bird Folks,

There are whole armies of fiddler crabs living in the marsh near my house. There are also lots of crows, gulls, herons, plovers, etc. I never see any of these birds going after the fiddler crabs. Don't the birds like them or are the birds eating them when I'm not looking?

-Dick, Wellfleet, MA

That's it Dick,

They are waiting for you to turn your back. The birds would love to eat the crabs but they are too polite to eat in front of you. Nobody likes to be seen with a mouthful of wiggling crabs. It's bad enough that marsh birds have to stick their faces into mud all day long without having the additional embarrassment of being observed with kicking legs hanging out of the corners of their beaks. Emily Post wrote an entire chapter on proper leg eating and clearly the marsh birds have read it.

Anyone who doesn't live near the coast, or who hasn't visited the coast, or who hasn't gotten a postcard from the coast, needs to know that fiddler crabs are small crabs that live in the mud of salt marshes. Fiddler crabs are so named because the males have one small front claw, while the other front claw is ridiculously huge. Early naturalists thought that the large front claw resembled a fiddle and they named the crab after it. Well, I don't know what they were thinking. If you ask me, that is no fiddle they are carrying. It's a viola, maybe. But a fiddle? I don't think so.

Most of us would think that the jumbo claw of the male fiddler crab would give it an advantage when it comes to catching food. At the very least, the larger claw could be used to catch and to rip apart prey. Well, for the most part the big claw is more of a hindrance than a help. Fiddler crabs obtain nutrients by eating the marsh mud. They feed by shoveling mud into their mouths with their smaller front claws. The females, with their two small claws, have a distinct advantage. They are two-fisted mud eaters. The males are forced to work twice as hard because they only have one small claw to eat with. When it comes to dinning, the large fiddle isn't much help, except to play lovely dinner music.

Why the big claw? It's a babe attracting implement. Why else? Fiddler crabs live in underground burrows. During the breeding season the males will hang out in front of their burrows and wave their large claw at all of the passing females. Strangely, this odd behavior actually works. More often than not, the females fall for the ol' waving claw trick and follow the males down into their burrows. What happens next we can only guess, as the males close the door behind them with a plug of mud. I think it is safe to assume that something good happens in the burrow because the next day both crabs are all smiles, which is unusual for crabs. Now that we have the crab lecture out of the way, we can go back to the birds. Just about every bird you mentioned, Dick, would love to make a meal out of a fiddler crab. Gulls, crows and herons are all opportunists. They'll eat just about anything that they can get their beaks on. That includes fiddler crabs. The problem for them is that the fiddler crabs can be tricky to catch. They rarely wander far from the safety of their burrows. At the first sign of trouble, they vanish deep beneath the marsh mud. Crows and gulls aren't particularly well adapted for fiddler crab hunting and apparently the rewards don't warrant the effort. They would rather look for a nice slow moving plate of French fries or a succulent discarded fish head.

Some birds, on the other hand, are built for eating fiddler crabs. Along the U.S. southern coast the White Ibis, with it's long downward curved bill, can easily dig out the fiddler crab from it's burrow. In your town of Wellfleet, migrating Whimbrels stop by every summer to eat fiddler crabs. The Whimbrel, which is a large shorebird, also has a down-curved beak that is perfect for snagging hidden fiddler crabs from their burrows, even with the mud door closed.

The reason you may not see these crab hogs feeding in your marsh, Dick, is because Whimbrels are a lot less common and more secretive than gulls and crows. They typically feed further out in the marsh, away from our eyes. They really do eat when you aren't looking. Gulls, on the other hand, would be happy to eat a fiddler crab or anything else while either you, me or Emily Post were watching. Heck, they'd probably even eat Emily Post if she was served with fries.

Artwork by Catherine Clark

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