Tuesday 3 February 2015

Common Tern x Forster's Tern

possible Common Tern x Forster's Tern hybrid (with Common Terns), Grand Isle, Lake Champlain (Vermont, USA), 22nd May 2013 - copyright Dave Hoag
(photo ID: 1800)

This bird was among 100 Common Terns but Dave tells us that this one was obviously much thicker-billed, paler-billed (and longer-billed?) yet lacked the longer and more orange legs of a Forster's Tern.  It's legs were red like those of Common Tern and Dave thinks its bill was maybe not orange enough for a typical Forster's Tern.

In additon Dave notes that the tail length relative to wing length was wrong for Forster's and the primaries were too dark.  The belly does seem white in all the photos.  No flight photos were obtained.

Dave tells us that Forster's Terns recently began nesting within a Common Tern colony on Lake Champlain - circumstances that make occurrence of hybrisation more likely than normal.

Common Tern Sterna hirundo
Forster's Tern Sterna forsteri

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