Noddies are members of the
tern family Sternidae in the genera
Anous,
Procelsterna, and
Gygis. They are a tropical group, characterised by the notch-wedge shaped (not forked) tail; coastal and pelagic oceanic. Studies of
mtDNA sequences (Bridge, 2005) have shown that the noddies are at least 2 groups that split off early from the ancestral terns at different points of time; the relationships of
Procelsterna were not researched for lack of samples. It seems to represent either a third lineage linking the noddies and the
marsh terns, or is closely related to
Gygis.