I have been seeing hundreds of robins during the last few weeks, both in  
Montgomery County and on the Eastern Shore in Kent County.  That got me  
thinking.  Years ago I heard an intriguing discussion about robin  migration.  There 
were two theories offered:
 
  1. Southward shift - This postulated that robins we see in the  winter were 
birds that bred to the north, say Nova Scotia or Newfoundland,  while "our" 
summer birds went further south to Florida.  In this theory all  Eastern 
Seaboard birds simply move several hundred miles to the south of where  they lived 
in the summer.
 
  2. Leapfrog - This theory suggested that "our" summer birds  stayed at 
roughly this latitude, although moved to appropriate areas where  there were lots 
of berries for winter sustenance.  The northern birds  leapfrogged in 
migration over "our" robin population to winter to the  south.
 
Does anyone know whether either of these theories has been proven by  banding 
returns or other research?
 
Bob Mumford
Darnestown