Barn-Nesting Birds in Summer Fields

     Barn swallows, house sparrows, rock pigeons and European starlings are abundant in Pennsylvania croplands from the end of June through the rest of summer.  These species are aliens to North America, except the swallows. 
     All four of those kinds of birds raised broods of young in barns and other buildings in farmland and now the young and older birds alike are getting food from surrounding fields, making that farmland the more interesting.  But these bird species rely on different foods in different parts of the croplands, reducing competition for it among themselves.
     Groups of the beautiful, purple and orange barn swallows catch small, pesky insects in mid-air over croplands.  The swallows zip along and weave among each other without collision, being quite   entertaining to human observers. 
     Between feeding forays, however, the barn swallows line up on the twigs of trees, corn stalks, roadside wires and the roads themselves to rest and preen their feathers.  They sit on the roads as they traditionally have done on beaches and mud flats, but lift off the road to avoid vehicles. But once in a while, one gets killed on a road.     
     Flocks of European house sparrows and their youngsters of the year perch in ripe, but not yet mowed, grain fields to feed on the grain on the seed heads at the tops of the stalks.  These plain, little birds are light enough in weight to stand on the stalks while eating.  Obviously, the swallows and sparrows don't compete for food. 
     House sparrows also perch on corn stalks between feeding, and they gather on roadsides to ingest tiny bits of stones to help grind the seeds in their crops and stomachs.  But when a vehicle approaches, they quickly fly into the corn and grain fields for refuge.
     Pairs and gatherings of rock pigeons, and their relatives the mourning doves, feed on grain in the fields, but only after the grain crop has been harvested by machinery.  These birds are too heavy to perch on the stems, so they are obliged to consume grain off the ground after the harvest.  Pigeons and doves also ingest little stones from the sides of country roads to crush the seeds in their crops and stomachs.         
     Groups of European starlings, and American robins and purple grackles, move about on harvested grain fields to pick up invertebrates on the ground that were exposed by the machinery removing the tall vegetation.  Here again, one can see that the starlings don't compete with the other types of birds in this grouping for food.
     Though barn swallows, house sparrows, pigeons and starlings rear offspring in Pennsylvania barns, flocks of them feed in surrounding fields without rivalry for food among them.  And those common, everyday birds make agricultural areas the more interesting to us human observers.