Why are procellariiform birds also called tubenoses?

Procellariiform birds are commonly referred to as "tubenoses" because of their distinct, conspicuous tubular nostrils that project upon the culmen, or upper bill. This physical characteristic is the basis for the order's alternative name, Tubinares, which translates to "tube-nosed".1

In most species within this group, the nostrils are fused into a single tube located on the dorsal midline of the bill, though in albatrosses, the two nasal tubes remain separated on the right and left upper lateral surfaces.2