1.9 years. Another pair of hirola mated when they were 1.7 years of age. In captivity one of the main causes of mortality is wounds caused by intra-hirola aggression, including aggression between females. Threats The reasons for the historic decline of the hirola are not known but is likely a combination of factors including disease (particularly rinderpest), hunting, severe drought, predation, competition for food and water from domestic livestock and habitat loss caused by bush encroachment as a result of the extirpation of elephants within its range. This hartebeest prefers areas that are used by livestock which puts them at increased risk from diseases like tuberculosis. It might be vulnerable to poaching, and is also subject to the natural phenomena of predation and competition with other wild herbivores, particularly topi and Coke's hartebeest, which the IUCN also calls 'threats'. Population size and distribution The hirola's natural range is an area of no more than 1,500 km2 on the Kenyan-Somali border, but there is also a translocated population in Tsavo East National Park. The natural population in the 1970s was likely to number 10,000–15,000 individuals but there was an 85–90% decline between 1983 and 1985. A survey in 1995 and 1996 estimated the population to number between 500 and 2,000 individuals with 1,300 as the most reasonable estimate. A 2010 survey estimated a population of 402–466 hirola. A translocated population was established in Kenya's Tsavo East National Park with translocations in 1963 and 1996 (Hofmann, 1996; Andanje & Ottichilo, 1999; Butynski, 1999; East, 1999). The 1963 translocation released 30 animals and the first survey in December 1995 concluded that there were at least 76 hirola present in Tsavo at the time. Eight months later a further 29 translocated hirola were released in to Tsavo, at least six of which were pregnant at the time (Andanje, 1997). By December 2000 the hirola population in Tsavo had returned to 77 individuals (Andanje, 2002) and by 2011 the population was estimated at 76 individuals. In 2013, 9 individuals from 7 different herds were fitted with GPS-collars, scheduled to drop-off in June 2014, in north-eastern Kenya. This marked the first time that the species was GPS-collared in the wild. These collaring events served as a purpose to understand the basic ecology, the natural history, movements patterns and population demographics of the species. Status and conservation Hirola are critically endangered and their numbers continue to decline