On the Tibetan Plateau
George B. Schaller, KANG Aili, CAI Xinbin, LIU Yanlin
The principal calving area is located in the hills south of the Shar Kul ('Kul' means lakes in Uygur) and Ser Kul basins, which are bordered by the main Kunlun Mountains on the north side. Female chiru are found mainly in an area of about 60 km east to west, from east of Shar Kul to just west of Ser Kul. Further west, chiru were few, as noted in 2001 and nearly all were males. By contrast, males were virtually absent on the calving ground: fewer than a dozen yearling (one-year-old), two-year-old, and adult males were seen by us. The main north to south calving area is narrow, only about 20km.
The whole area is extremely barren, with many hillsides lacking vegetation, and the slopes of sand, silt, and soil constantly eroding. The principal plant is a low shrub, no more than 10-15cm high, named Ceratoides compacta (In Chinese: Dian Zhuang Tuo Rang Li). This is the only plant available as food to chiru over large areas especially in late May and June when the migration arrives. Transects showed that ground coverage of Ceratoides is sparse and varies from less than 1% to 5% with 95% to over 99% of the ground bare.
The number of yearling and adult females that calve in this area is difficult to determine with precision. The area is large and mountainous, the animals are constantly on the move, and our team was too small to count the chiru in all parts at the same time. Between June 25-27, we observed a total of 2360 in the main calving area on the plateau and western part of the large basin, but no doubt overlooked many. Later, between July 2-7, when snowstorms drove most animals out of the nearby hills there, our tally was about 2130. However, by that time the southward migration was in progress: we saw a herd of about 1000 in the hills to the south on July 5. Therefore, we would guess that at least 3000 chiru, yearling and adult females were in that concentration area during calving. There were at this time also chiru scattered elsewhere in the hills and parts of the Shar and Ser Kul basins. For example, on July 5, a total of 246 were still counted in the basins. This suggests that perhaps 4000-4500 chiru were present in the area.
In 1992, between July 20 and August 3, at least 7350-7750 chiru passed Tibet Aru basin on their way south, as intermittent counts showed, and it was estimated that the population was "over 10,000;” of these, about 4500 were young born a month earlier, leaving over 7500 yearling and adult females. Assuming that our 2005 estimate is reasonably accurate, this chiru population has declined considerably in the past decade. It is also possible that some females calve elsewhere now. Reliable counts need to be made of this population in Tibet.
Status of Newborns
The first newborn was observed June 18 and the last July 7. The main birth period in 2005 appeared to be between June 24 and July 3. Newborns generally weigh 2.5-3.5kg.
It was noted in mid-June that although the calving time was near, many adult females were not heavily pregnant. We assumed that the calving period was longer than the anticipated birth. However, later counts of percent of adult females with and without calves showed that many females did not give birth. Precise statistics are difficult to present because females tend to segregate themselves to some extent, with females and newborns staying together in certain part of the hills and others elsewhere. We calculated that about 35-40% of females had newborns. In other words, nearly 2/3 of females lacked a young. Some newborns had died. But whether the population has a disease, perhaps obtained from livestock in Tibet, or if a hard winter reduced fertility last year is not known.
Yearling females (one-year-old) can be distinguished from adults by their smaller size. They do not reproduce until 2 years of age. Many yearlings separate from their mothers on the calving grounds. (Yearling males already separated in May, most before the migration). The: yearling females then may join into small groups and wander in areas other than the main calving ground. Thus, our counts of yearlings varied from place to place and indicated that about 10-20% of the females were yearlings with an average of about 16%. Assuming that yearling males elsewhere occur in equal numbers, about one adult female in three had a surviving young. Reproduction appeared to have been better in 2004 than 2005.