Curlews, Clams, and Calcium

Long-billed Curlew

Long-billed Curlew

The next time you visit the beach or a river sandbar, test your dexterity by using a pair of chopsticks to locate, capture, and extract some small clams from their subsurface burrows.

You may find that the experience will give you a new respect for what Long-billed Curlews commonly do with ease.

Razor clam headed to the gullet

Razor clam headed to the gullet

Of course the curlews do not have access to the grocery store, so if they want to eat they have to use their noggins and bills effectively.

As I watched these birds foraging in the shallow waters at low tide in the San Diego River channel of Southern California, several thoughts occurred to me.

On the way

On the way

First, how do the birds recognize a target site to probe?  They seem to totally ignore some areas and lightly touch or shallowly probe other areas before they really get down to business.

Could such things as taste and smell be involved in locating a clam?  What about vibrations in the sand as a clam tries to burrow deeper?

Last minute adjustments

Last minute adjustments

Second, how does a curlew catch and capture an actively burrowing clam without getting a beak full of sand?

As the curlews probe deeply, the birds appear to twist their heads and bills in a corkscrew fashion which may simply be following the path of the clam or it may provide some torque for their bills.

Another clam

Another clam

Third, how does a curlew generate enough force to grasp and hold onto a slippery clam shell?  Perhaps the curve of the bills comes into play here.

When bent against the grain, curved objects seem to be capable of generating force to return to their original shape when the stresses are released.  For common examples one can think of springs, archery bows, and some flatbed trailers used in the trucking industry.

Adjusting the grip

Adjusting the grip

Whatever the source of energy, the bill must grasp the clam shell firmly enough to hold it against the suction of the sand or mud as the bill is extracted.  Maybe this is why one sees few, if any, long-billed shorebirds with straight bills.

Fourth, if the clam had the capability to jet itself down through the sand in burrowing deeper, why does it not try to do the same as it is being extracted by a curlew?  Also, for the occasional clam that the curlew drops onto the riverbed before swallowing it, why does the clam not use its jets to spurt away?

Whoops!

Whoops!

Could it be that the clams are stunned by the suction forces generated when the curlews finally open their bills as they contact the subsurface clams?  Although the mechanics are probably different, both large-mouth bass and alligators can capture nearby prey items by suddenly opening their mouths and letting water currents suck the prey into their waiting jaws.

In the water!

In the water!

Fifth, are the clam shells that are swallowed used as a source of calcium for developing egg shells?  If so, is clam eating confined to female Long-billed Curlews or do males participate as well?

Could it be that calcium-supplying clam habitats are a critical part of a Long-billed Curlew’s life history, and that population dynamics for these birds can depend on the availability of these habitats.  Could it also be that past and current distribution patterns and ranges for this species can be partially explained by reviewing the distribution of these clamming areas?

Let's try this again

Let’s try this again

Paraphrasing Mark Twain, science is fascinating as one can generate so much speculation from so few facts.  While these questions currently have the status of being personal working hypotheses, I may eventually find evidence to accept or refute them.  When or if that happens, the following quote (attributed, I believe, to one of the Huxleys) may apply:   “Another beautiful hypothesis killed by the ugly facts.”

Until then, keep at it with the chopsticks.

You can view the video at https://youtu.be/Ckj55Yvy700

Ahhh!  There's nothing like a good clam!

Ahhh! There’s nothing like a good clam!

 

 

 

 

 

 

 

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