 Pelicans give their name to the Pelecaniformes , an order which has a varied taxonomic history . Tropicbirds , darters , cormorants , gannets , boobies and frigatebirds , all traditional members of the order , have since been reclassified : tropicbirds into their own order , Phaethontiformes , and the remainder into Suliformes . In their place , herons , ibises , spoonbills , the hamerkop and the shoebill have now been transferred into Pelecaniformes . Molecular evidence suggests that the shoebill and the hamerkop form a sister group to the pelicans , though there is some doubt as to the exact relationship between the three lineages . 
