Common, Migrant Sandpipers

     Most of us think of sandpipers being on beaches along the seacoast, and some species are there to feed on invertebrates in every season.  But many kinds of sandpipers are also in coastal salt marshes when the tide is out and along the muddy shores of inland waterways and impoundments to consume invertebrates, particularly during their migrations north in spring and south in late-summer into autumn.  And two species of sandpipers, least sandpipers and lesser yellowlegs, are the most common of their large family of shorebirds in southeastern Pennsylvania during their trips south to escape the northern winter.
     Coming south from nesting territories in Canada and Alaska, many individuals of least sandpipers and lesser yellowlegs pass through this area every late-summer and fall.  They don't leave northern latitudes to escape frigid temperatures, but do so to find reliable sources of invertebrates in shoreline mud and shallow water in Central America, South America and the Caribbean area.  But they have to stop on their way, now and again, to fill up on invertebrates to have the energy to continue their migrations south.  Various-sized flocks of both species stop along the muddy edges of waterways and impoundments, but mostly in flooded fields and meadows after heavy or prolonged rains.  Land-based invertebrates emerge from the inundated ground to avoid drowning, but many of them are eaten by these two common types of sandpipers, other kinds of shorebirds in lesser numbers, and other species of birds, including American robins, mallard ducks and starlings.
     The brown least sandpipers and gray lesser yellowlegs, like most species in their family, blend into their open niches almost perfectly.  In spite of a total lack of cover to hide behind, these species usually are not seen until they move across the ground or water, or take flight.  Camouflage is essential for them so they are not spotted by fast-flying peregrine falcons, merlins and other kinds of hawks that would attempt to kill them to eat, if they saw them.  But shorebirds, including least sandpipers and yellowlegs, are also speedy on the wing, swerving this way and that as a group, which confuses hawks and allows the shorebirds to dash to camouflaged safety on another muddy shore or flooded field.                  
     Sparrow-sized least sandpipers are brown with darker streaking which camouflages them on muddy shorelines.  They have dull-yellow legs which identify them from other kinds of small, brown sandpipers.  Least sandpipers walk about together in varying-sized flocks on the mud and in inch-deep water to use their beaks to pull tiny worms and insects from the mud, even that which is under water.     
     Least sandpipers raise young on the ground in the treeless Arctic tundra.  Each female lays four eggs in a clutch that hatch into open-eyed, fluffy, camouflaged chicks that are ready to run and feed themselves within hours of hatching.  That camouflage protects the young, and their parents, from predators including Arctic foxes, gulls and jaegers.
     Lesser yellowlegs are about the size of American robins, but leaner in shape.  This kind of sandpiper stands on long, yellow "stilts".  Yellowlegs are mostly gray with white speckles which blends them into the water they wade through to probe for aquatic invertebrates with their long, slender bills.  Their long legs get them into deeper water than what least sandpipers can handle.  And the yellowlegs' lengthier beaks allow them to probe deeper into mud than the least sandpipers can.  Therefore, the different bodily features allow each species to exploit a slightly different niche, which reduces competition for food between them.   
     Each pair of lesser yellowlegs raises four young in a brood around ponds and bogs in the boreal forests of northwestern Canada and eastern Alaska.  And they winter in wetlands from the central latitude of the United States south to southern South America. 
     I enjoy seeing flocks of least sandpipers and lesser yellowlegs on the muddy shores of waterways and impoundments, and especially in flooded fields and pastures in southeastern Pennsylvania late in summer and into autumn.  Those interesting sandpiper flocks in this civilized area, like all migrant birds, are ambassadors to much of the world.  And it's intriguing to see these northern, wilderness shorebirds using inland, human-made niches such as impoundments and inundated fields and meadows while on migration.  Their adapting to those built habitats increases their populations and our outdoor pleasure.