Connections: Birds and Crabs, Part IV

As you might imagine, eggs that lay buried in the sand have the greatest likelihood for survival.  Eggs driven closer to the surface have the least likelihood for survival due to any number of environmental factors (lack of moisture, lack of adherence), but also because they become more readily available for shorebird consumption.  There’s also another factor at play here – the length of the shorebirds’ bills.  For example, red knots (whom you will meet shortly), one of the most prevalent of the migrating shorebirds, have some of the longest bird bills – on average 1.3 inches long.  Thus, they can forage in moist sand and extract any eggs within 1.3 inches of the surface.  Obviously, eggs buried deeper are beyond their reach and thus considerably safer and considerably more viable.
            You might think that the length of the red knot’s bill would deny it access to any of the deep-buried eggs.  Not so.  For, if nothing else, the red knot are opportunistic feeders – in short, they allow others to do all their work for them.  In this case the workers are the other horseshoe crabs who dig and scrape and mess around the nests of previous females – disturbing and excavating previously-laid eggs as they try to lay their own eggs.  Being the first to lay one’s eggs isn’t always a good thing – it may subject those eggs to the “digs” of females who follow.  Archeologists sometimes experience something similar  when they discover an ancient city that has been built on the ruins of a previous ancient city which has been built on the ruins of yet another ancient city.  A succession of spawning females – all nesting at approximately the same spot on the beach – has the potential to release thousands and thousands of eggs from each of the previous nests and onto the beach.  The more eggs released, the more eggs available for consumption – even by birds with short bills.