The Black-bellied Tern (Sterna acuticauda) is a tern

Tern

Terns are seabirds in the family Sternidae, previously considered a subfamily of the gull family Laridae . They form a lineage with the gulls and skimmers which in turn is related to skuas and auks...

 found near large rivers in South Asia

South Asia

South Asia, also known as Southern Asia, is the southern region of the Asian continent, which comprises the sub-Himalayan countries and, for some authorities , also includes the adjoining countries to the west and the east...

. They have a black belly in the summer and a deep forked tail. They can sometimes resemble Whiskered Tern

Whiskered Tern

The Whiskered Tern is a seabird of the tern family Sternidae. This bird has a number of geographical races, differing mainly in size and minor plumage details....

s but the deeper fork and the black on the lower belly distinguish it from the shallow fork and black closer to the breast on the Whiskered Tern. Considering that mtDNA sequence

DNA sequence

The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...

 analysis supports moving the similar Black-fronted Tern

Black-fronted Tern

The Black-fronted Tern also known as Sea Martin, Ploughboy, Inland Tern, Riverbed Tern or Tarapiroe, is a small tern generally found in or near bodies of fresh water in New Zealand and forages for freshwater fish, arthropods and worms. It has a predominantly grey plumage...

("Sterna" albostriata) into Chlidonias, this species might also be better placed in that genus, but no research has yet been conducted.