Roofvogels van het Tibetaans Plateau in 1988-2001

The Tibetan Plateau was visited annually between 1988 and 2001, mostly for periods of 3-4 months each year, sometimes for 4-7 weeks and once, in 1995, for 7 consecutive months. Except for a single summer, all visits took place in autumn, winter and spring. As logistics are difficult in this region, transportation was mainly by yaks or horses, accompanied and helped by monks who also acted as mediators between the local people and the visitors. Main objectives were to experience cultures relatively untouched by modem society, as well as studying ungulates and birds. Over the years, observations accumulated which were often at variance with presentations in field guides, handbooks and papers dealing with the region. Some of these observations are presented in this overview. The Tibetan Plateau covers about 2.5 million km² (Fig. 1), of which 50% exceeds 4500 m above sea level (85% above 3000 m). Of 810 lakes, 600 are to be found in the central range, the Chang Tang. Some lakes are huge, as the Kokonor Lake in the north (at 3200 m above sea level, 4400 km2). Most lakes have substantially decreased in size in recent years due to a decline in precipitation, often becoming salt along the way. Borders of fresh water lakes abound with waterbirds during migration and winter. Less than 1% of the Tibetan Plateau is presently cultivated, although locally – as in the Quadam Basin – this area has increased due to enforced settlement. Cultivated land is mostly confined to areas below 3300 m, but reaches an altitude of 4400 m near Yarlung Tsangpo. Permafrost is typical of the northern regions, penetrating as deep as 155 m; only the top layer of 50-60 cm becomes defrosted during summer. More than 30% of the Chang Tsang consists of Alpine- and steppe vegetations, dominated by Slipa species and Carex moorcroftii. The land climate is harsh, and even extreme above 4500 m (-40°C quite normal). In Shigatse and Lhasa temperatures are rather moderate compared to the Chang Tang. Wintering conditions in Ladakh are especially harsh because settlements and lakes are situated at higher altitudes than elsewhere in the region; temperatures of -50 to -60°C in January and February are not unusual. At similar heights in Tibet, the climate is equally harsh but as villages and lakes on average are situated at lower altitudes, living conditions are less harsh and many lakes are not (completely) frozen, offering opportunities for wintering waterbirds. Apart from extreme coldness, dust storms are typical of the region. On average, the local Bhuddist peoples live in harmony with their environment, as evident from the absence of hunting and fishing and the holy status of several lakes and bird species. Flowever, the “untamed” Goloks in the central Chang Tang are fierce hunters, responsible for almost exterminating species like Brown Bear Ursus arctos, and seriously depleting populations of Wild Yak Bos grunniens, Argali Ovis ammon, Bharal Pseudois nayaur, Tibetan Gazelle Procapra picticaudata, Chiru Pantholops hodgsoni and Urial Ovis orientalis. These depredations were especially devastating during the aftermath of the Cultural Revolution in the 1970s and 1980s. Although large areas are nowadays officially protected nature reserves (some as large as 334,000 km2), at the same time the Chinese government encourages settlers to invade the area. Where formerly wild animals populated the region, their stocks are now much depleted and cultivated animals like sheep and goats (30 million by 1990) and domesticated yaks (12 million ditto) have taken over. The presence and relative abundance of raptors in Tibetan and Ladakh parts of the Tibetan Plateau have been summarised in Table 1. It should be noted that observations during summer are limited to a single year, that conditions for observation are often difficult and that birds were only a sideline of research while staying in the area. Species-specific details are provided below. Black Kite Milvus migrans: passage migrant in large numbers in Tibet and China, with flocks of tens staying temporarily along rivers. Pallas’s Fish Eagle Haliaeetus leucoryphus: only observed in the Tibetan part of the range, i.e. an adult and juvenile on 3 October 1998 at Tar Tso (31°10'N, 84°0), a juvenile on 10 April 1995 at Am Co and an adult accompanied by a juvenile on 4 September 1995 at the Manasarovar Lake. Egyptian Vulture Neophron percnopterus: adult singles were recorded near Lhasa on 6 January 1993, and on 4 April near Paiku Tso (29°N, 85°50’). Himalaya Griffon Gyps himalayensis and Eurasian Griffon G. fulvus: both species were heavily persecuted in the aftermath of the Cultural Revolution, as in the Tibetan district of Gansu. Both are still in dire straits. In recent years, a slight increase in the number of breeding pairs has been noted, especially in the vicinity of Lhasa and Shigatse (but not in Gansu). This resulted from a change in the attitude of the Chinese government towards the existence and use of open-air burial sites (where vultures used to be fed with the corpses of the deceased); mercilessly destroyed in the late 20th century, some have now been re-opened, as in Lhasa. Red-headed Vulture Sarcogyps calvus: although formerly present on the Tibetan Plateau, it is now a rare bird, not showing an improvement in status compared with both Gyps species. Northern Goshawk Accipiter gentilis: mostly seen during migration. Birds passing in March and April are often harassed by territorial Sakers. White-eyed Buzzard Butastur teesa: twice recorded on Chang Tang (once dead, on 2 October 1992 near Nyalam, just north of Kathmandu, another in October 2001 in the same area). A third bird was seen on 18 October 1998 near Lunggar (31 °N, 84°O). Upland Buzzard Buteo hemilasius, Long-legged Buzzard B. rufinus and Common Buzzard B. buteo: the presence of these species is correlated with the distribution and abundance of pikas (notably Ocholona pusilla and O. curzionae). Large numbers of pikas are associated with ditto numbers of voles, providing excellent feeding conditions for buzzards. Rough-legged Buzzard Buteo lagopus: more common in winter than depicted in field guides and handbooks (as holds for many other wintering species). Steppe Eagle Aquila nipalensis: like buzzards depending upon presence and abundance of pikas, but also recorded at concentrations of waterbirds. Spotted Eagle Aquila clanga: commoner in winter than usually depicted in guides and handbooks. Preference for areas with large concentrations of waterbirds. Golden Eagle Aquila chrysaetos: on two nests in the Chang Tang region remains of the Steppe Tortoise Agrionemys horsfeldi were collected. Although this prey species is commonly captured (and killed by dropping it from great heights on rocks below) in eastern Kazakhstan, it is apparently absent from the Chang Tang (as confirmed by the local people). Eurasian Kestrel Falco tinnunculus: a ubiquitous species, occurring everywhere as a breeding bird and even present at high altitudes with extremely low temperatures in winter. Amur Falcon Falco amurensis and Red-footed Falcon F. vespertinus: respectively rarely seen and passing during migration. Laggar Falcon Falco jugger: never observed during the early 1990s, observations have increased in recent years with almost annually records nowadays, even in late autumn and in early spring. Saker Falco cherrug: present all-year round, especially in the Chang Tang. Juveniles disperse from the area. Territory defence starts already late January, irrespective of temperature. Breeding starts as early as the beginning of March. Twice a Saker was recorded as being killed by a Eurasian Eagle Owl Bubo bubo hemachalanus; in one such case, the owl simply dropped onto a breeding Saker which was taken by surprise. Gyr Falcon Falco rusticolus: one bird, which had broken its wing against a nomad tent on 27 February 1992 near Dinggo (33°20’N, 84°40’E), three other birds were recorded in the central Chang Tang between 32-34°N and 83-87°E, on 22 February 1995, 26 February 1995 and 1 December 1998 respectively.