Een vreemd verband tussen Tibetaanse Steenuilen Athene noctua ludlowi en Himalayamarmotten Marmota himalayana in West-Tibet en Zuidoost-Ladakh

The Tibetan Owlet population in Ladakh is estimated at 120 pairs, occurring up to 4100-4550 m on the Tibetan Plateau where so-called hotspots are occupied, i.e. rock deserts with lakes of varying sizes, volcanic springs and a rather luxurious vegetation dominated by Stipaand Caragana-species. In January and February, temperatures may drop to -55°C. Snowfall is normally very restricted (<10 cm) and starts by mid-November. However, dust devils are of frequent occurrence, and are equally devastating as snow storms in Siberia. For several years, we have been studying Wild Ass Equus kiang populations in eight hotspots (2 in SE-Ladakh, 6 in West-Tibet), their favourite habitat. Four such hotspots (1 in SE-Ladakh, 3 in West-Tibet) also held small populations of Tibetan Owlets, with 6-8 pairs each. In this type of habitat, Tibetan Owlets nest in rock cavities. (Ladakh, Tibet) and in monasteries (Tibet). Densities of Tibetan Owlets in West-Tibet are also small, but its distribution is much wider there. The Tibetan Owlet on the Indian subcontinent is restricted to Ladakh; elswhere in the Indian subcontinent it is replaced by the Spotted Owlet Athene brahmani, which in our experience does not occur above 2300-2400 m. The hotspots were also visited in autumn and winter 1997/98, 1999/2000 and 2001/2002. In late September 1997, we noticed a remarkable change in behaviour of Tibetan Owlets along the Manasarovar Lake in West-Tibet. This holiest of lakes (in the believe of Tibetans and Indians) has a circumference of some 90 km and a water temperature of 2C all year long. Up till then, the owlets stayed in front of their breeding cavities or on top of stone walls. From late September onwards, they began showing an interest in the burrows of Himalayan Marmots Marmota himalayana, which they tried to enter. They were chased away until the marmots started their hibernation by mid- October. From then on, the owlets frequented the burrows of the marmots where they resided up to a depth of one meter. The owlets of a hotspot some 30 km away from the Manasarovar Lake showed an identical change in behaviour, as did the owlets in a hotspot in SE-Ladakh in the autumn-winter of 1999/2000. The latter case was particularly interesting, as many burrows were not occupied by marmots following a population crash in the winter of 1997/98. The owlets were only interested in burrows occupied by marmots, and therefore had to wait till the marmots started their hibernation. The population crash was caused by early (mid-September) and heavy (1.5 m of snow by mid-December, as compared to a normal snow depth of 10 cm or less) snowfall in 1997, which – for example – almost halved the population of Wild Ass in Ladakh (from c. 1500 to 800 at most). Melting snow flooded many burrows in spring, wiping out some 80% of the Himalayan Marmots at a hotspot in Tsokar (Ladakh) and eliminating the entire, and largest, colony of c. 120 pairs near Pang, a village c. 80 km south of Tsokar (where the species was still absent in spring 2002). Also Woolly Hares Lepus oiostolus and Black-lipped Pikas Ochotona curzionae suffered from these spring floods. The Tibetan Owlets, however, survived the freak weather, presumably by moving to lower altitudes (normally strictly resident).