Rockwood River, Ontario, Canada
postmarked in 2009 with a machine stamp
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I'm assuming these are Canadian Geese :D
Canada geese are known for their seasonal migrations. Most Canada geese have staging or resting areas where they join up with others. Their fall migration can be seen from September through the beginning of November.
These geese are also renowned for their V-shaped flight formation. There is no 'leader' - The front position is rotated since flying in front consumes the most energy. They fly in that formation because it is aerodynamic.