The stomach is a complex four-chambered structure with a ruminant type digestion although the animal does not chew the cud. The ecological requirements for hippopotamus, therefore, include a supply of permanent water large enough for the territorial males to spread out, and adequate grazing on open grassland within a few kilometres of the daytime resting sites. The hippopotamus is thought to be decreasing in 18 of the 34 countries considered although doubt is expressed over this point in four cases. The species is increasing in only two countries, Congo and Zambia. The former is probably unimportant for the conservation of the species but Zambia certainly is not.
Populations are stale in another six countries with the trends unknown in a further eight.
The number of countries is less important than their identities. Most of the declines are in West African countries with small populations but two East African countries showing declines, Uganda and Zaire, contain some of the largest populations. The decline does not appear to be serious or widespread in Zaire for not all correspondents reported one. The decline in Uganda occurred during the recent political troubles are now seems to have halted. Populations there are probably stable at present and may be expected to start increasing before long.