Geoscience Reference
In-Depth Information
birds from small to tall stick their beaks into the sand to probe for, pry out, and
procurefoodstuff.Muchofthissustenanceconsistsofsmallclams,snails,andcrus-
taceans, which burrow into the sand in a vain attempt to avoid predation. (As far as
these invertebrates are concerned, shorebirds might as well be tyrannosaurs.)
When used in combination with tracks, beak-probe patterns can even be at-
tributed to specific birds, such as sandpipers, plovers, or sanderlings. For instance,
sandpipers do double taps—bang-bang—which leave distinctive two-holed pat-
terns. In contrast, plovers keep their beaks on a beach surface while running along
at high speed, making a more continuous and connected series of holes.
With clams, oysters, and other bivalves, more subtle traces of bird predation
might be on the shells themselves. Look for chipping along shell edges, revealing
whereshorebirdswedgedintheirbeaksandthenopenedthem,anactioncalledgap-
ing; this exhausts an assaulted clam, which eventually can't resist any longer and
opens its valves, revealing its soft goodies inside. Further evidence of gaping might
be apparent where clams are still in their burrows but all that is left are two empty
valves. Sometimes these valves—still joined at their hinges—have been pulled out
of their burrows and left lying on a beach surface like open books, perhaps with
a valve holding a small pool of clam juice. The final piece of ichnological and
forensic evidence linking a shorebird with these molluscan molestations are their
tracks, which help to identify which species pried into these clams' personal lives,
then ended them.
Do these methods seem a little cruel to us? Sure, but they work great for birds.
Infact,here'ssomethingevenmorebrutal:Someofthempickuptheirintendedvic-
tim—either a thick-shelled clam or whelk—fly up to a height of 5 to 10 m (16-33
ft), and drop it onto concrete or hard-packed sand. Thick shell or not, few mol-
luscans can withstand this aerial-assisted assault, and their shells will either break
or at least the animals will be stunned enough by the impact that they open up. I
have often seen traces of this predation along the Georgia coast, in which a seagull
prowledasandflatatlowtide,extractedaclamorwhelkfromitsburrow,heldonto
