Not always a big fan of Wikipedia for accuracy, however this is interesting.
"The traditional term for a male falcon is tercel (British spelling) or tiercel (American spelling), from Latin tertius = third because of the belief that only one in three eggs hatched a male bird.[2][3] Some sources give the etymology as deriving from the fact that a male falcon is approximately one third smaller than the female[4] (Old French tiercelet)."
Thanks for finding the picture of the Wilson's Phalarope, RCF. I've never heard of this bird, so it's nice to have a face to the name.