Cape Town Pelagic, Cape Province, South Africa, August 1, 2007. Here is another shot of White-chinned Petrel. This individual has no evident white on its chin at all. From this close angle, the distinctive plates which form the bill can be seen. The top plate at the base are the forward-facing tubes which are characteristic of seabirds in the order Procellariformes. The function of these tubes is debatable. It has been suggested that they contain valve-like pockets which allow the birds to exploit winds of varying speeds during dynamic gliding, but evidence for this hypothesis is lacking. A supersaturated saline solution excreted by salt-glands behind the forehead passes out through these tubes. This mechanism may allow seabirds to drink sea-water. However, other species of birds also have salt glands yet do not have tubular nostrils. Canon PowerShot S3IS.