Baijis have long been recognised as one of the world's rarest mammals, and are extremely shy animals, making observation of them in the wild extremely difficult. Consequently, relatively little is known of the species (6). They are most active through the night from early evening to early morning (3). They tend to live in small groups of three to four individuals, with the largest group ever seen comprising of 16 (2). A recent study found that they often swim with finless porpoises (Neophocaena phocaenoides), the only other cetacean in the Yangtze River, which is also threatened (classified as Endangered on the IUCN Red List) (1) (6). Baijis break the surface of the water without creating a splash and breathe smoothly (2). They feed on a wide range of freshwater fish (2), which are eaten whole (7).
It is thought that breeding occurs in the first part of the year, with most births peaking between February and April (2).