within five months if the cubs of the previous litter are lost. The mortality rate of tiger cubs is about 50% in the first two years. Few other predators attack tiger cubs due to the diligence and ferocity of the mother. Apart from humans and other tigers, common causes of cub mortality are starvation, freezing, and accidents. Generation length of the tiger is about eight years. The oldest recorded captive tiger lived for 26 years. Occasionally, male tigers participate in raising cubs, usually their own, but this is extremely rare and not always well understood. In May 2015, Amur tigers were photographed by camera traps in the Sikhote-Alin Nature Reserve. The photos show a male Amur tiger pass by, followed by a female and three cubs within the span of about two minutes. In Ranthambore, a male Bengal tiger raised and defended two orphaned female cubs after their mother had died of illness. The cubs remained under his care, he supplied them with food, protected them from his rival and sister, and apparently also trained them. Conservation In the 1990s, a new approach to tiger conservation was developed: Tiger Conservation Units (TCUs), which are blocks of habitat that have the potential to host tiger populations in 15 habitat types within five bioregions. Altogether 143 TCUs were identified and prioritized based on size and integrity of habitat, poaching pressure and population status. They range in size from . In 2016, an estimate of a global wild tiger population of approximately 3,890 individuals was presented during the Third Asia Ministerial Conference on Tiger Conservation. The WWF subsequently declared that the world's count of wild tigers had risen for the first time in a century. Major threats to the tiger include habitat destruction, habitat fragmentation and poaching for fur and body parts, which have simultaneously greatly reduced tiger populations in the wild. In India, only 11% of the historical tiger habitat remains due to habitat fragmentation. Demand for tiger parts for use in traditional Chinese medicine has also been cited as a major threat to tiger populations. Some estimates suggest that there are fewer than 2,500 mature breeding individuals, with no subpopulation containing more than 250 mature breeding individuals. India is home to the world's largest population of wild tigers. A 2014 census estimated a population of 2,226, a 30% increase since 2011. On International Tiger Day 2019, the 'Tiger Estimation Report 2018'