CASPIAN TERNS VS COMMON TERNS, WINDERMERE BASIN,HAMILTON,ONTARIO, 7/18/2020

   In these three photos we can see the differences between the two most common Terns in this area - the Caspian Tern and the Common Tern. 
   In the first photo the smaller Common Tern is on the right and the much larger Caspian Tern is on the left.  The Caspian Tern is much larger than the Common Tern - 21" vs 12".  Also, in the Common Tern the black crown extends down the nape, while in the Caspian Tern it doesn't.  In this photo you can't see the bill of the Common Tern.
   The Common Tern in the second photo is the single small tern on the right; a large group of Caspian Terns is on the left.  In the third photo there are two small Common Terns on the left, the rest of the Terns are Caspian Terns.

   Another was to tell the difference is the size of the bill, it is larger and thicker in the Common Tern.  This a particular usefull field mark in flight.  Another usefully field mark in flight is the tail.  Common Terns have a forked tail, while Caspian Terns have a slightly notched tail.
   Caspian Tern's legs are always black, while Common Tern's legs are reddish in fresh juveniles and breeding adults, but black in nonbreeding adults and 1st year birds.
   

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