Biological Conservation 65 (1993) 29-34 POPULATION VIABILITY AND MANAGEMENT RECOMMENDATIONS FOR WILD WATER BUFFALO Bubalus bubalis IN KOSI TAPPU WILDLIFE RESERVE, NEPAL Joel T. Heinen* School of Natural Resources, University of Michigan, Ann Arbor, Michigan 48109-1115, USA (Received 11 March 1991; revised version received 25 October 1992; accepted 27 October 1992) Abstract Population characteristics, breeding structure, and sources of mortality of wild water buffalo Bubalus bubalis were studied in Kosi Tappu Wildlife Reserve, a small reserve located in the southeastern lowlands of Nepal, during 1987 and 1988. Comparisons with an earlier census indicated that the population was growing over a 12-year time interval. However, observations on the physical nature of the reserve and known seasonal movements of buffalo suggested that the population is not viable for several reasons. Most morality observed during the study took place over the rainy season, suggesting that flooding was the major source; half of the first-year calves dis- appeared during that time. Because the reserve was subject to extensive flooding during the rains, buffalo regularly left to reside in cane and sugar fields. Hence the reserve did not include the annual home range of any buffalo herds. In addition, thousands of domestic cattle and hundreds of domestic buffalo used the reserve illegally, which posed a risk of disease to wild water buffalo. Management recommendations, including a re- introduction of the species into Royal Chitwan National Park, are made in light of the analysis. Key word~." Nepal, wild water buffalo. INTRODUCTION With the passage of the 1973 National Parks and wildlife conservation act (Anon., 1977), Nepal began an era of committing resources for the conservation of species and protected areas. The Act and subsequent amendments now give full protection to 26 mammals, eight bird, and three reptile species. Of primary concern to wildlife professionals is how policies and management practices can lead to the long-term survival of these endangered populations in increas- ingly isolated, fragmented landscapes such as those found in South Asia (e.g. Seshadri, 1986; Heinen & * Present address: FREE, 4900 25th Street NE, Suite 201, Seattle, WA 98105, USA. Biological Conservation 0006-3207/93/$06.00 © 1993 Elsevier Science Publishers Ltd, England. Printed in Great Britain Kattel, 1992). As Goodman (1987) pointed out, study- ing management measures and reserve-design features for small, fragmented populations is desirable for esti- mating and enhancing population viability; several field studies (e.g. Mwalyosi, 1991; Yonzon & Hunter, 1991) have shown that reserve characteristics, as well as conflicts with local people, can influence long-term viability of populations. In this study, the population growth rate, sources of mortality, population structure, seasonal movements, and important aspects of social behavior relevant for conservation of wild water buffalo Bubalus bubalis were studied over a 1.5 year period (November 1986 to March 1988) in Kosi Tappu Wildlife Reserve, a small reserve located in southeastern Nepal. This species was studied because it is protected in Nepal and elsewhere and is presently limited to this single isolated population within the country. There is no immigration or emigration and the species is highly polygynous, so this example readily points out the problem inherent to maintaining adequate effective breeding population sizes (Are) for many large mammals. Furthermore, the population was studied in two different time periods (Dahmer, 1978, and the present study), which allowed comparison of the instantaneous population growth rates at different times. 29 THE SPECIES AND STUDY AREA Wild water buffalo are ancestral to domestic water buffalo widely used as dairy and draught animals in Asia and parts of North Africa and Europe (Cockrill, 1974). Evidence of domestication goes back 4500 years (Clutton-Brock, 1989), when the species ranged from Mesopotamia to Indochina (Sinclair, 1977). Wild water buffalo historically occurred throughout much of the lowland parts of South Asia in suitable riverine forests and grasslands but are now considered endangered throughout their range. Several large populations are found in Indian reserves such as Kaziranga National Park in Assam and Indravati Wildlife Sanctuary in Madya Pradesh (Saharia, 1982), but the species has been extirpated from large portions of its former range. The current worldwide population is now estimated at