Migrant Swallows and Bonies

     It happens every year during the latter part of March and into early April.  Flocks of tree swallows and groups of Bonaparte's gulls migrate up the Susquehanna River in southeastern Pennsylvania.  They are going to their breeding areas farther north and west and creating interesting natural spectacles along the river at the same time that is fun for me to watch each spring.   
     Those many swallows daily stop here and there on the wing low over the river to catch hatches of flying insects to fuel their bodies for the next part of their migration north to their nesting territories.  There those hundreds and hundreds of swallows create entertaining natural spectacles of themselves.  They swiftly swoop, turn and dive after flying insects among their many fellows, without ever having a collision with them.  Birds low to the river seem to dance on the water.  We can see the swallows rowing with powerful wing beats into the wind for flight control, then sweeping up and around with the wind, and powering into it again.  All that in fast, direct flight for extended periods of time until the swallows are full of insects.  Then they rest for awhile and eventually push north again.
     Tree swallows are handsome birds, particularly in flight.  Males are iridescent blue on top and immaculate white below.  Females are blue-gray above and off-white underneath.
     Tree swallows traditionally hatch young in abandoned woodpecker cavities and other tree hollows, often near bodies of water or waterways.  And they have adapted to nesting in bird boxes erected for eastern bluebirds.  Often a little gang of tree swallows gangs up on a pair of bluebirds and chases it away from a nesting site so a pair of swallows can use that place themselves.
     Young tree swallows fledge their nurseries toward the end of June.  By the end of July flocks of tree swallows begin to gather for their migration south to escape the northern winter when they won't be able to find insect food.  And great gatherings of thousands and thousands of them pass through this area during August, September and into October.  At that time, we often see hordes of them lined up and resting on roadside wires for hundreds of yards or flying in swarms over fields and meadows to catch flying insects.  Their autumn migrations are just as intriguing as their spring ones.  
     Bonaparte's gulls are small gulls, and fast fliers.  They winter around back waters off the Atlantic Ocean where they catch small fish from the surface of the water.  Each spring, many small groups of bonies power swiftly  up the Chesapeake Bay and the Susquehanna, as they do other rivers, to get to their breeding grounds in western Canada and Alaska.  Sometimes they stop here and there along a river to catch small fish near the surface of the water or insects lying on the water before those birds continue their migrations.
     Bonies are easily identified by the broad, white stripe they have on each gray wing.  In flight, those stripes look intriguingly like many banners fluttering together in the wind.
     In winter, Bonaparte's gulls are light gray on top and white below with a black mark behind each eye.  Many spring migrants are still in their winter plumage when they come through here in migration.  But some have part of their summer feathering when we see them here in spring.  Bonies' more attractive summer plumage includes having a black head and red legs.
     Migrating tree swallows and Bonaparte's gulls are almost guaranteed along the Susquehanna River in late March and into much of April.  They are beautiful and intriguing to watch along the river at that time and make this area, in general, a bit more interesting.