Swallow Nesting Habitats

     Next month six species of swallows will enter the Middle Atlantic States to raise young.  These locally nesting swallows, like other forms of life, demonstrate the benefits of species of related critters diverging into different habitats to reduce competition for space and food with their relatives. All species of swallows catch flies, mosquitoes and other types of flying insects to feed themselves and their offspring, but where those different kinds of swallows nest is what keeps them apart; keeps them from competing with other swallows for food.
     Swallows nest in three niches in this region, which separates them from their relatives.  Those niches are barns and bridges, which is a departure from small caves and cliffs whee they have traditionally nested, tree cavities and bird boxes, and holes in banks of soil and drainage pipes over waterways.
     All swallows are graceful and swift on  the wing.  They have to be to chase down and grab flying insects.  And their fast, swooping, back and forth flights over open country, including farmland, are entertaining to us.       
     Barn swallows and cliff swallows are aptly named because the first species rears young in cradles plastered to support beams in barns and under bridges over small waterways in farmland as they do in small, shallow caves.  Cliff swallows hatch offspring on the sides of buildings and bridges as they do on cliffs.  Each species forms small colonies to raise offspring, thereby taking the best advantage of the limited space they use for nesting. 
     Both species make nurseries of mud pellets.  Each bird of every pair of both kinds roll mud pellets in their beaks and fly them up to their nurseries.  There they put each pellet in place for their nest.  The barn swallows make an open cup, while the cliff swallows create an enclosed, jug-shaped nest with a hole in the side just big enough for the birds to slip in and out.
     Barn swallows are common in local farmland, nesting in most every barn and small bridge in the region.  But cliff swallows are not common here, having few nesting colonies.  Both species are deep-purple on top and pale orange below, with differences in details between the species.
     Tree swallows and purple martins both had reared young in abandoned woodpecker holes and other tree cavities.  Tree swallows still do, but the martins are completely tied to human-made bird boxes and gourds that people put out for them.  Male tree swallows are metallic-blue on top and white below, while male purple martins are a deep purple all over and their mates are smoky above and off-white underneath.
     Tree swallows can nest as individual pairs and in small, loose colonies, depending upon the number of cavities available to them in a region.  And they not only hatch youngsters in natural cavities, but in bird houses, as well.  Those bird boxes were erected originally for eastern bluebirds to raise young, but many tree swallow pairs take over bluebird boxes and chase away the bluebirds.  Sometimes a few pairs of tree swallows gang up on a pair of bluebirds to drive them off.
     Purple martins always live in tight, sometimes large, colonies in the farm yards of cropland.  Certain people erect apartment bird houses and/or strings of gourds for the martins, though starlings, house sparrows and other kinds of birds also want to use those bird boxes.  Most of the summer the martins keep up a constant activity of catching insects, and a chatter that is pleasant to people who enjoy those largest of swallows around their homes.
     Bank swallows and rough-winged swallows are both brownish species that hatch youngsters in hollows in stream banks.  The bank swallows live in colonies and each pair digs a burrow in a stream bank of soil above the normal waterline where they rear their young.  Individual pairs of rough-wings dig tunnels in stream banks, too, but they also raise babies in abandoned kingfisher burrows and drainage pipes in stream banks.  Those pipes are safe homes for developing youngsters until heavy rain is conducted down the pipes, washing out young, nest and all.
     All these swallow species in the local area, except maybe the bank swallows, probably have higher population numbers now than ever in their life histories.  That is due to their adapting to human-made conditions.  And all these swallow species, particularly the more common barn swallows, tree swallows and purple martins, are entertaining to us.  This spring and summer, or succeeding ones, watch for these beautiful, entertaining birds that catch insects in graceful flight.