NESTING ON STRUCTURES

     Several kinds of adaptable birds raise young on human-made structures in southeastern Pennsylvania, as elsewhere.  Though they all originally nested in other, natural niches, they found structures to be common, handy shelters for their offspring.  Those birds gain additional nesting sites, and an increase in numbers.  And they help make built niches more interesting to us.

     Mourning doves, house finches and house sparrows are abundant, seed-eating birds that build nurseries in sheltering places on buildings in suburbs and cities.  Some pairs of doves, for example, rear youngsters in pots of flowering plants hanging under deck and porch roofs.  House finches build grassy cradles on supports under awnings above decks and porches.  And house sparrows build their bulky nests of grass in any available crevices they find on structures. 

     Pairs of starlings raise youngsters in cracks in buildings, in traffic lights hanging over streets and other built structures.  Starlings are one of the ultimate birds at adapting to what is available.    

     Wild rock pigeons, American kestrels and barn swallows, all farmland residents in summer, nest in protective barns and under sheltering bridges.  Pigeons originally nested on sea cliffs above the Mediterranean Sea, kestrels in tree hollows and the swallows on cliffs and in the mouths of caves.  Tree cavities and caves offer ample protection.  But so do barns and bridges, which have increased the numbers of these birds since colonial days in the United States.    

     Carolina wrens raise young in all kinds of sheltering places, including on shelves in garages and sheds, under decks and porches, stone walls and crevices in buildings.  These lively, warm-brown birds with energetic songs originally reared progeny in brush piles and among boulders in bottomland woods.        

     Eastern phoebes originally nested on rock shelves under overhanging boulders near water in woods.  But they soon adapted to nesting on support beams and other objects under sheltering porch and pavilion roofs and small bridges in woods, which suited their nesting needs.  Support beams are like rock ledges and roofs are like overhanging boulders. 

     Chimney swifts build cradles on the inside walls of some chimneys in towns and cities.  They snap off tiny, dead twigs from trees while in flight and glue those twigs with their saliva to the inside chimney walls to make a nursery.  Swifts traditionally nest down the insides of hollow trees, but quickly adapted to protective chimneys as a great and abundant substitute for hollow trees.  There probably are more chimney swifts alive today than in colonial times in the United States.

     Rough-winged swallows raise young in drains under bridges.  They originally nested in abandoned kingfisher holes in streambanks over waterways, or little tunnels they dig out themselves in streambanks.  But they soon adapted to drainage holes under bridges that span waterways as an abundant substitute for burrows in streambanks.  These gray-brown swallows often are associates of the equally-hued phoebes under bridges. 

     Killdeer plover hatch chicks on gravel bars along streams and on bare soil in fields.  But they have adapted to hatching babies on gravel driveways and parking lots, flat, gravel roofs and railroad beds, and on spreadings of mulch.  Like all these birds in this writing, killdeer are more common than ever because of an increase in nesting sites created by people.  

     There are other kinds of birds that benefit from the workings and structures of people, including least terns and nighthawks nesting on flat, gravel roofs.  Adapting is a key to success, including nesting on built structures.  And we can enjoy those adaptable birds right at home.