mid-adulthood and then begins to decline. However, this can depend on the ranking of the male within their group, as higher-ranking males maintain a higher rate of reproduction. Most observed matings are by males in musth over 35 years of age. Twenty-two long observations showed that age and musth are extremely important factors; "… older males had markedly elevated paternity success compared with younger males, suggesting the possibility of sexual selection for longevity in this species." Males usually stay with a female and her herd for about a month before moving on in search of another mate. Less than a third of the population of female elephants will be in estrus at any given time and the gestation period of an elephant is long, so it makes more evolutionary sense for a male to search for as many females as possible rather than stay with one group. Threats Both species are threatened by habitat loss and fragmentation, and poaching for the illegal ivory trade is a threat in several range countries as well. The African bush elephant is listed as Endangered and the African forest elephant as Critically Endangered on the respective IUCN Red Lists. Based on vegetation types that provide suitable habitat for African elephants, it was estimated that in the early 19th century a maximum of 26,913,000 African elephants might have been present from the Sahel in the north to the Highveld in the south. Decrease of suitable habitat was the major cause for the decline of elephant populations until the 1950s. Hunting African elephants for the ivory trade accelerated the decline from the 1970s onwards. The carrying capacity of remaining suitable habitats was estimated at 8,985,000 elephants at most by 1987. In the 1970s and 1980s, the price for ivory rose, and poaching for ivory increased in particular in Central African range countries where access to elephant habitats was facilitated by logging and petroleum mining industries. Between 1976 and 1980, about raw ivory was exported from Africa to Hong Kong and Japan, equivalent to tusks of about 222,000 African elephants. The first continental elephant census was carried out in 1976. At the time, 1.34 million elephants were estimated to range over . In the 1980s, it was difficult to carry out systematic surveys in several East African range countries due to civil wars. In 1987, it was estimated that the African elephant population had declined to 760,000