SWIFTS AND SWALLOWS

     Chimney swifts and four kinds of swallows are interesting to watch on the wing to catch flying insects with their beaks during the warmer months here in Lancaster County, Pennsylvania, as elsewhere.  All migrants that wintered farther south, these small, streamlined birds sweep and swerve swiftly and gracefully through the air much of each day, every day, to catch their prey, and creating a show that people can enjoy.
     Although swifts are related to hummingbirds, they are built more like swallows because of convergent evolution.  Swifts and swallows have nearly identical lifestyles in a shared habitat, which shapes them into similar-looking creatures to make the best use of that habitat.  Both groups of small birds are streamlined and have long, powerful wings and flight muscles for swift, sustained flight.  And both groups have large mouths for their body size so they can snare their prey on the wing.    
     Swifts generally are higher in the sky than the swallows when gleaning insects from the air, which reduces competition among these birds for food.  And, although these birds weave speedily among their fellows while snaring flying insects, I've never seen them collide with each other.  They obviously have quick reflexes.
     These insect-eating birds are also interesting in their adapting to feeding and nesting in human-made habitats, including farmland, cities and suburbs.  Swifts and swallows are probably more abundant today because of that adapting than they ever were in their life histories.
     Chimney swifts traditionally raise young in protective hollow, broken-off trees in the eastern United States.  But these adaptable birds are now nesting down the inside of certain chimneys, which, to them, are like hollow, broken-off trees.
     Each pair of smoky-hued swifts in flight snaps off tiny, dead twigs from trees and glues those twigs to the inside wall of a chimney to make a cradle for their young, using their own saliva as a glue!  Parent swifts feed insects to their offspring on those twiggy platforms.  And the first flights of young swifts need to be good to exit the chimneys they were born in.
     Great swarms of post-breeding chimney swifts swirl, round and round, over large chimneys in cities and suburbs around sunset each evening in August.  Round and round, each horde of swifts spins over its chimney of choice, with numbers of swifts dropping into the gaping, sky-pointing hole with each pass.  At first, a few swifts enter the chimney, then more and more with each spiral until the remaining revolving mass of birds sweeps down the chimney like smoke in reverse.  Now all the swifts are down their protective, vertical shelter for the night, each bird clinging upright with its tiny, sharp toe nails imbedded into the rough surface of the chimney's inner wall.
     In September, flocks of swifts migrate south to northern South America where they spend the northern winter catching flying insects.  But next April, they will be back in the United States again, ready to raise young.
     Barn swallows are so-named because they raise young in mud-pellet nurseries plastered to support beams in barns and under small bridges in farmland.  They traditionally nested on cliffs and the mouths of caves in North America.  But they obviously have adapted to building their mud cradles in human-made structures.        
     Barn swallows pick up mud in their beaks and fly each mud pellet, one at a time, to their nest site on the side of a support beam, where they plaster that pellet to the beam.  They make a cup-like structure with an open top to receive their eggs.  Adults feed their progeny flying insects.
     Barn swallows are iridescent purple on top and orange below, with males having deeper colors than their mates.  These swallows scatter over farmland to catch flying insects and line up on roadside wires between feeding forays to rest and digest.  By August, they begin gathering for their migration south to Central and northern South America to pass the northern winter catching flying insects.  But they will be back in North America the next April. 
     Tree swallows and purple martins traditionally hatch chicks in tree cavities in North American cropland, the former species in single hollows, while the colonial-nesting martins need multiple holes near each other.  Single bird houses are erected for tree swallows to nest in, while apartment bird boxes are erected for martins.  Those built cavities have greatly increased the numbers of the adaptable tree swallows and martins over the years.
     Tree swallows and martins are attractive as they zip over meadows, fields and lakes after flying insects.  Male tree swallows are iridescent blue on top and white below, while their mates are more grayish above.  Male martins are iridescent deep-purple all over while female martins are gray on top and dingy-white underneath.
     Tree swallows and martins also line up on roadside wires between feeding forays and during their migrations south for the winter.  Sometimes large numbers of each kind are seen on wires, causing great spectacles, as they rest and digest the insects they caught.
     Rough-winged swallow pairs are look-alikes, with both genders being gray-brown.  Traditionally, individual pairs of these swallows either dig nesting holes in stream banks, or use abandoned belted kingfisher burrows in those same stream banks to raise youngsters.
     Today, some pairs of rough-wings nest in drainage pipes under bridges over smaller waterways and in retaining walls at waterways.  Those human-made nesting sites are fine until heavy rain flushes out young, grassy nursery and all.  Some pairs start over, if it is not too late in the season.
     Swifts and swallows are interesting to observe catching insects in the air.  And they have intriguing life histories.  And they are built similarly because they share a niche of careening through the air after flying insects.