The question of the week in New Scientist (Feb. 12-18, 2011) is, "The blue-footed booby is an extraordinary-looking bird. It has fairly dull plumage but strikingly coloured blue legs and feet. What could be the evolutionary benefit of such a conspicuous feature? Both sexes have blue feet so they don't seem to be for impressing potential mates."
This is bound to bring out the adaptationists. You can be almost certain that the answers will consist of various just-so stories based on the assumption that blue feet have to be an adaptation. Can you make up a good adaptationist story to explain the blue feet? It doesn't have to have any supporting evidence. Try and avoid explanations that rely on sexual selection—that's too easy.
The evolutionary relationship between the various booby species is shown below in a figure take from Friesen and Anderson (1997). The Peruvian and blue-footed boobies apparently diverged from a common ancestor about 200,000 years ago. The Blue-footed booby's range is northern Peru and the Peruvian booby lives in southern Peru. They do not form hybrids where their ranges overlap.
[Photo Credit: Wikipedia]
Friesen, V.L. and Abderson, D.J. (1997) Phylogeny and Evolution of the Sulidae (Aves: Pelecaniformes): A Test of Alternative Modes of Speciation. Molec. Phylo. Evol. 7:252-260 [doi:10.1006/mpev.1996.0397]