< Cristol speculates that a small shell isn't worth the energy required to
drop
it because it doesn't contain much meat, while a large clam is meatier but
too heavy to carry. >

        I have watched the gulls dropping clams many times, but my
impressions of why they select medium-size clams is a bit different from the
above.  The reason they don't take large clams, in my opinion, is not the
weight of the clam, since I have more, than once seen a gull fly off with
quite a large fish (certainly well over a pound) in its beak.  I think the
problem with large clams is that the gull's bill simply can't get a grip on
a large, hard, rounded object.  It's like trying to grasp a large pipe with
a pair of needle-nose pliers - they just slide off, while a smaller object
can be grasped securely.  As for the rejection of smaller clams, I don't
think it is energy conservation that is involved, so much as the difficulty
in breaking the darn things.  The smaller clams just don't have enough mass
to generate enough kinetic energy to provide enough of a collision to cause
much damage (my apologies to both students of physics and students of
english grammar).  A small Mercenaria dropped from a considerable height
onto a paved road will just bounce, while a larger one will land with a
splat, shattering the shell into several pieces.  A clam three times the
length may have ten times the mass, and since they are both moving at the
same speed, the large one carries a lot more energy.  Just imagine the
difference between a 1-ounce clam and a 1-pound clam hitting your windshield
(this HAS been known to happen in areas where vehicle parking and gull
feeding overlap), or your head!

        Paul M.