Another name for Chionis minor is sheathbills. These birds are known for their fowl-like body shape. They have uniformly white plumage. They have short legs, a compressed bill and facial carunicles. These chunky birds are identical to doves only that they are larger. They have a unique horny sheath.

Description

Only two species exist within this genus. The habitat is mostly coastal plains, ice floes and intertidal zones that are sandy and rocky. In terms of conservation status, this bird is categorized as not threatened. It is mainly found in South America.

Evolution

Today, you will mostly come across this bird in sub Antarctic islands, Southern South America and in the Antarctic Peninsula.

In terms of morphology, sheathbills are rather peculiar and distinct birds. Their behavior and distribution hints to the same conclusion. However, research has led many to conclude that this bird is a member of Charadriiformes. This is an order with very diverse groups that consist of shoebirds, waders and gulls. For one, the relationship between the sheathbill and all the other members of this order are yet to be resolved. This issue therefore remains very contentious among taxonomists.

Many researches done in recent times are centered on behavioral, biochemical and morphological approaches. These approaches seem to be adding to the ambiguity rather than helping resolve it. The DNA hybridization studies that were done in 1990 were a source of an impending breakthrough. In this research, sheathbills were categorized as belong to a sister group whose memberships is made up of the likes of all plover-like birds, scientifically known as Charadriidae as well as thickknees, also known as Burhinidae.

However, the hybridization studies were marred by very sharp criticism in terms of validity of the methodologies applied. The main source of contention was the manner in which genetic comparisons were made between nuclear and mitochondrial DNA. Proper comparisons of genetic material are believed to be the only way in which this contention will be resolved in the future.

Fossil evidence

Sheathbills are found in area where it is very difficult to come across any fossil evidence. It therefore becomes difficult to estimate where they could have originated from. Some taxonomists believe that these birds radiated during the Miocene epoch or even much later. This period is more than 30 million years ago.

There is a very close association between seabird and sheathbills in terms of morphology. Seal colonies are also believed to have a very strong influence in the evolutionary path of these birds.

Classification

Sheathbills belong to a single genus, which has two easily recognized species. These species are the black faced sheathbills and pale faced sheathbills. There is no overlap in terms of their ranges. In fact, further differences are often singled out as far as physical characteristics and migratory behaviors are concerned. The black faced sheathbills are often categorized into four distinct subspecies depending on geographical distribution in different islands and archipelagos.

Physical appearance

The main distinguishing feature of sheathbills is stocky appearance, the white plumage that uniformly covers the whole body, and the unique sheathed bill.