SAHARA OASIS SWALLOWS

      Barn swallows, tree swallows and other kinds of swallows live and migrate across much of North and South America.  And barn swallows, and house martins, which are another species of swallow, live and migrate between Europe and Africa.  These swallows migrate from central Africa, north over the Sahara Desert to nest in Europe during spring, and do the opposite in late summer to spend the winter in Africa.    

      But getting across the Sahara would be a big problem for both these species if there were not palm tree-lined oases among the unending and dry sand dunes along the way.   Those swallows get food and drink from those oases that will refresh them, and sustain them in their travels.  Without those oases that bubble to the surface, here and there, from ground water, the swallows would die along the way. 

      Many oases, however, have water more salty than the oceans because it is stagnant, and trapped between sand dunes.  Their water would poison any creatures that drank from them.  So how do the migrating swallows get fresh water for the next part of their long trips north, or south?  Those swallows get adequate food and fresh water by catching in their mouths, in mid-air, some of the millions of adult brine flies that live along the edges of oases.  Those flies are the only way the swallows can migrate across the Sahara Desert!  

     Larval and mature brine flies ingest the salty water because that is all that is available to them.  But they adapted to being able to expel the salt in that water.  Therefore, the migrant swallows only get fresh water when they ingest adult flies on the wing.  

     Aquatic-living larval brine flies feed on algae, diatoms, bacteria and detritus in the salty water.  The larvae soon metamorphosis to winged adults and mostly live on the surfaces of oases waters.  Mature flies ingest a little algae, but are mostly interested in reproducing themselves during their short lives as adults.  But many of them are consumed by migrating barn swallows and house martins.     

     All swallow species are handsomely streamlined and have swift, graceful and maneuverable flight essential for capturing dodging insects on the wing.  Feeding swallows in entertaining, airborne flocks of themselves weave in and out among their fast-flying fellows with never a mid-air collision.  They are well built and adapted to what they do for a living.

     The relationship between the flies and swallows at an oasis is another of innumerable miracles of life surviving in extreme conditions: What a wonderful world has been created! 

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