SKY SWEEPERS

      Some early evenings in August, I sit on our deck in New Holland, Pennsylvania and watch several each of barn swallows and chimney swifts sweeping swiftly across the sky in on-going, hot pursuit of flying insects to eat.  Those entertaining birds start me thinking about the creatures in southeastern Pennsylvania that regularly chase flying insects.  Those summering critters in this area are four kinds of swallows, including barn swallows, tree swallows, purple martins and rough-winged swallows, chimney swifts, a few common kinds of dragonflies and a few species of bats.  These airborne kinds of local wildlife are inspiring to watch careening across the sky, and among their fellows in mid-air, without collision, over cities, suburbs, fields and impoundments after their prey.  Swifts and all the swallow species have broad mouths to snare their victims.  And the attractive swallows line up on roadside wires to rest, digest and preen their feathers between feeding forays.  

     Each type of swallow has its own nesting niche, which reduces competition for food and scattered nesting sites among those related species.  Barn swallows plaster mud pellet nurseries to the sides of support beams in barns and under small bridges, which, to them, resemble the cliffs and cave mouths they traditionally nest in.  Tree swallows nest in tree cavities and bird boxes.  Martins hatch young in apartment bird boxes that are, to them, like standing dead trees full of abandoned woodpecker holes.  And rough-winged swallows rear offspring in deserted kingfisher burrows in stream banks, and in drainage pipes under bridges that, to the rough-wings, are like holes in stream banks.    

     By mid-August, many hundreds of barn swallows congregate into flocks to hunt flying insects as those swallows slowly drift south to escape the northern winter when flying insects are not available.   And during September, thousands of tree swallows pass through southeastern Pennsylvania on their way south, snaring airborne insects along the way every day.  Both species of migrating swallows are intriguing to experience, especially when sweeping low over fields after insects and when these birds are perched in long rows on roadside wires.  

     Chimney swifts, as their name implies, nest down the inside of chimneys, which, to them, are like hollow, broken-off trees where they traditionally raise young.  Swifts break off tiny, dead twigs from trees while those birds are in flight.  They glue those twigs to sheer walls inside chimneys to create platforms for their eggs, using their own saliva as the glue.  

     The soot-covered swifts, generally, flutter and glide, turning this way and that at high speed, high in the sky in pursuit of flying insects.  Still, one can hear their twittering from the ground.  Swifts sky-high flight is always entertaining, particularly toward sunset, and the swifts' higher flight reduces rivalry for food with the lower-flying swallows.  

     Each evening, during much of August, when nesting is finished for the season, swifts gather in great masses at dusk and swirl, time after time, over a large chimney.  Eventually, some swifts leave the spinning wheel and shoot down the gaping opening.  Soon more and more swifts follow the leaders down the chimney until the turning mass of them spiral the hole, looking like rising smoke in reverse.   

     A few kinds of larger dragonflies, especially green darners, catch flying insects in mid-air over the ponds where they were naiads, and over all other local habitats as well.  Those fast-moving dragonflies are also entertaining and inspiring to notice in action, wherever they may be.    

     A few kinds of bats, particularly little brown bats, are the night shift of sky sweepers.  They take the sky-wide stage soon after sunset, as the hard-working swallows, swifts and dragonflies retire.  Bats are entertaining to watch, even as mere silhouettes against the darkening sky.  They dash, swoop, dive and make sharp turns in pursuit of flying insects.  I sometimes lie on a driveway to more comfortably watch bats' aerial maneuvers until they can no longer be seen.  And, currently, we see a few little brown bats from our deck in New Holland.

     These interesting, entertaining sky sweepers are built to catch flying insects.  They are small, light in weight and highly maneuverable on the wing.  They are all fascinating to experience         

        

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