The grey noddy is sometimes considered to be a morph of the blue noddy. These are grey-plumaged noddies that are endemic to tropic regions of the Pacific Ocean. They nest colonially and feed on small fish picked from the surface.
A molecular phylogenetic study published in 2016 found that the five noddies formed a single clade with the two species in Procelsterna embedded among the brown noddy, lesser noddy and black noddy in the genus Anous. The authors proposed that the noddies should be merged into a single genus Anous and that Procelsterna should be considered as a junior synonym.
- Gill, Frank; Donsker, David, eds. (2017). "Coursers, noddies, gulls, terns, auks & sandgrouse". World Bird List Version 7.1. International Ornithologists' Union. Retrieved 16 April 2017.
- Cibois, A.; Thibault, J.-C.; Rocamora, G.; Pasquet, E. (2016). "Molecular phylogeny and systematics of Blue and Grey Noddies (Procelsterna)". Ibis. 158: 433–438. doi:10.1111/ibi.12363.