Chapter 5: Chitawan National Park, Nepal
The American biologist Melvin E. Sunquist, Smithsonian Institution, Washington, D.C., has studied the tiger in the Royal Chitawan National Park, in Nepal. This Park lies in the Rapti Valley in the Chitawan District, near 27°30’N and 84°20’E. The valley is bounded in the north by the Mahabharat Lekh (outer Himalayan Range). The park covers an area of 544 km² (200 mi²). He reports about his findings in, “The Social Organization of Tigers (Panthera tigris) in Royal Chitawan National Park, Nepal, Smithsonian Institution Press, City of Washington 1981:
“The estimated crude density of adult tigers within the original park (544 km²) boundaries is one per 36 km², in the expanded area (932 km²) it is one per 30 km². Areas of prime habitat, however, or those containing an interspersion of riverine forest and grassland support higher tiger densities. For example, a 62 km² area in the southeast had four residents or one per 15.6 km², another area (91 km²) at the western end had one adult per 22.7 km². A recent survey by J.L.D. Smith (1978) showed that in a 245 km² area of prime habitat there were at least 18 tigers over two years of age, or one animal per 13.6 km². Preliminary survey in areas (i.e., sal forest) lacking the interspersion of habitats indicates they support only about one third the density recorded in prime habitats.” Sundquist, M.E. (1981:199.
The tiger is only able to live as a resident, to have a home range, and to raise its young, where there is a large enough prey biomass of hoofed animals during the first months of life of its cubs. Their mother must stay then close to them within her 18 km² home range, within an area of only 0.6 to 9.6 km². When raising cubs in their first year of life on her 18 km² home range, she needs a prey biomass of at least 3431 kg/km². In an arctic climate this is not possible. There is too little food.
“Tiger reproduction in Chitawan is high, as at any given time during the study most resident tigresses either had young or they were pregnant. Of the eight resident females, individually identified in1976, no fewer than six had a total of 14 young. J.L.D. Smith (1978) reports that of eight resident females in April 1978, seven had a combined total of 20 young and the other was probably pregnant. High productivity in Chitawan accounts for the surplus; more animals are reaching maturity than there are available vacancies (resident mortality), and the rapid filling of vacancies suggests that reproduction will be sustained at the current high rate.” (1981:20).
“Although the data on cub mortality are limited, it is probably not unreasonable to assume, … that the mortality rate during the first two years of life is at least 50%. By comparison with two lion prides in the Serengeti, Schaller (1972) estimated a minimum mortality rate of 67% during the first year of life.” (1981:23, 24).
“Daytime stalking requires suitable cover, which for the lion is a combination of terrain and/or vegetation of at least 41 cm in height (Elliot et al. 1977). A similar combination of vegetation/terrain may be necessary for the tiger, as one was observed stalking four chital at mid-morning in an open grass area, where the cover was only 30 cm high, and it was unsuccessful.” (1981:3).
“There is a gradual increase in range size as the young get older, but the effect of young on the female’s movements is evident for some time. … On the flood plain of Chitawan, both male and female tigers maintain exclusive ranges; the larger male ranges (60-100 km²) overlapping three to six smaller female ranges (16-20 km²). …
“The maintenance of relatively small, mutually exclusive ranges in Chitawan appears to be favored primarily by a seasonably stable prey population that is more or less evenly distributed throughout the flood-plain environment. Date from radio-tracking shows that sambar, chital, and hog deer, the major prey species, confine their movements to small areas (0.5-10 km²), where they are apparently able to satisfy their resource requirements on an annual basis. In addition, prey density and biomass are high, a characteristic of alluvial plain habitats. … On the floodplains in Chitawan: Female ranges were between 16-20 km² versus 60-100 km² of a male’s.” Sunquist, M. E. (1981:50-53).
“The only prolonged social contact in the tiger is that of a female and her dependent offspring. The young remain with the female until they are between 12-20 months of age. In their second year the young spend progressively more time away from their mother, with young males tending to travel alone at an earlier age, until they are nutritionally independent. … Body weights of Chitawan tigers, Nepal: Adult females: 143 kg, 153, kg, 159 kg, 130 kg, 143 kg. Adult males above 127 kg.
“Most of the prey killed by tigers weighed about 50-100 kg, but animals the size of adult sambar and domestic buffalo (160-400 kg) were regularly taken. … By comparison, most of the prey killed by leopards residing in the same area weighed about 25-50 kg. … 30% of large prey body weight is gut contents.” Sunquist, M.E. (1981:62, 69, 75, 76).
A king’s tiger moving along at a leisurely trot, but it will change into a “flying gallop”, when chasing after a fleeing prey animal. From: Grzimeks Enzyklopädie (1987:10).
How heavy is the tiger, which lives in the Chitawan National Park, in Nepal, close to the foot-hills of the Himalayas? How heavy is it? How much must this large cat eat? How large is there the home range of the residential tigress, raising cubs? And how much ungulate prey biomass must her home range at least contain?
The Chitawan Valley is densely populated with tigers. So, each residential tigress can have there only about as much prey biomass, as she needs for herself and her cubs. A residential male tiger controls there the home range of several females. Wildlife biologist Melvin E. Sunquist found out:
The tigress, without young, must eat 5-6 kg meat/day on a yearly basis. To this, 30% waste must be added. The male tiger needs 6-7 kg meat/day. The tiger in Chitawan removes 8-10% of the wild ungulate biomass, or an average 9%. The adult tigress must kill 2600 to 3300 kg/year prey biomass, or an average 2950 kg/year. The adult male tiger must kill 3100 to 3700 kg/year prey biomass, or an average 3400 kg/year (wet weight).
4 small tiger cubs in their first year of life need as much food as one adult tigress. Each small cub in its first year of life needs ¼ as much prey biomass, as one adult female. The adult tigress must kill then 2950 kg/year prey. One cub in its first year of life (or 6 months old) needs 738 kg/year live prey. Two small tiger cubs in their first year of life need 1475 kg/year live prey; 3 small cubs in their first year of life need 2214 kg/year, and 4 small cubs 2950 kg/year live prey.
Home range of adult male tiger in Chitawan National Park, Nepal: 60-72 km². That of the female, with small cubs or when pregnant, 16-20 km², or an average 18 km². Sunquist, M.E. (1981). The average adult male tiger in Chitawan Valley weighs about 227 kg. The adult tigress 148 kg. The 6-month-old tiger cub weighs about 23 kg.
The American wildlife biologist John Seidensticker (1976) found out, when studying the tiger in Chitawan Valley: The tigress, raising cubs, usually has her home range on the flood plains, close to the river. The flood plain has about 2798 kg/km² prey (without the rhino). The average home range of the residential tigress in Chitawan is about 18 km².
Mel E. Sunquist and Fiona C. Sunquist report under the title, “Ecological Constraints on Predation by Large Felids” in Carnivore Behavior, Ecology, and Evolution, John L. Gittleman, Editor, 1989 London:
“Prey distribution in space and time is a critical factor for maternal females because they are initially confined to an area near the den and are thus restricted in their foraging radius. Field data on leopards, tigers, mountain lions, and ocelots (Felis pardalis) show a dramatic reduction in the maternal home range immediately following the birth of cubs. Under these conditions females must locate and kill prey, feed, and return to the den every 24-36 h (Seidensticker et al. 1973; Seidensticker 1977; M. Sunquist, pers. observ.). Thus, prey distribution and ‘catch-ability” (Bertram 1973) are vital to females in the first two months of maternal dependence when cubs are largely immobile. The young of large felids are nutritionally dependent on their mother for one to two years.” (1989:286)
“The presence of stalking cover directly influences the distance traversed in the final charge. Elliott et al. (1977) suggest that 0.4 m of grass cover is necessary for successful daytime lion hunts. Van Orsdol (1984) stated that lion hunting success increased with grass height up to 0.8 m, and Schaller (1972) found that lions hunting in grass 0.3-0.6 m high were twice as successful as those hunting in grass less than 0.3 m high.” (1989:290)
Tigress carrying her small cub in her mouth. From: Ronald L. Tilson et al. (eds.), Tigers of the World (1987:395).
How much ungulate prey biomass does the residential tigress in Chitawan Valley need on her 18-km² home range, when raising 2 cubs in their first year of life? That is, when they are about 6 months old? How much does the whole tiger family need, that is the ruling male tiger, and the tigress with her two cubs?
Residential male tiger, 227 kg body weight (BW). He needs 6.5 kg meat/day: 2.863% BW/day. He must kill then 4.091% BW/day ungulate prey (with 30% waste): 9.286 kg/day, and 3400 kg/year live prey. He takes in this model one third of his food from the female’s home range: 1133 kg/year (wet weight).
Residential tigress, 148 kg BW, non-reproducing. She needs 5.5 kg/day meat, 3.716% BW/day. She must kill then 5.308% BW/day ungulate prey: 7.856 kg/day, and 2950 kg/year live prey.
Two cubs in their first year of life (6 months old). One cub in its first year of life needs 738 kg/year live prey, and 2 cubs 1475 kg/year live prey.
The whole tiger family in Chitawan Valley must kill on its 18-km² home range 5558 kg ungulate biomass in one year. That is 9% of the total live prey: 61.756 kg/18 km² or 3431 kg/km².
This means: The residential tiger, raising 2 cubs in their first year of life, needs a prey biomass of large hoofed animals (up to the water buffalo) of at least 3431 kg/km².
When raising 3 cubs in their first year of life, the tiger family will need a prey biomass of hoofed animals of at least 3887 kg/km². In an arctic climate this is not possible. There is too little food.