Blue-grey Noddy - BirdForum Opus

The Blue Noddy Procelsterna cerulea and the Grey Noddy Procelsterna albivitta are recognised as separate species by Dickinson² and Clements¹; Sibley & Monroe³ treated them as conspecific under the English name Blue-grey Noddy.

References

1. Clements JF. 2007. The Clements Checklist of Birds of the World. 6th ed., with updates to October 2008. Cornell University Press. ISBN 9780801445019
2. Dickinson EC (ed.) 2003. The Howard & Moore Complete Checklist of the Birds of the World. 3rd ed. Princeton Univ. Press, Princeton, NJ, USA. ISBN 9780691117010
3. Sibley CG & Monroe BL. 1996. Birds of the World, on diskette, Windows version 2.0. Charles G. Sibley, Santa Rosa, CA, USA.