Daily Defecation Rate of Captive Axis Deer

Abstract

The South Asian axis deer, or chital (Axis axis), is a medium-sized deer (4565 kg) of the forest edge. Recent surveys indicate that the chital is the most abundant wild ungulate in many of the newly created wildlife reserves of the Indian subcontinent (Schaller 1967, Spillet 1967, Krishnan 1972, Berwick 1974, Sharatchandra and Gadgil 1975, Dinerstein 1980). The chital has been identified as the most important prey item in the diet of the endangered tiger (Panthera tigris) where the 2 species occur sympatrically (Schaller 1967, Muller and Zurcher 1973, Martin 1978). An understanding of predator-prey relationships requires accurate information on chital populations. Obtaining estimates on chital population sizes, densities, and age structures has been a major objective of several South Asian research efforts over the last decade (Berwick 1974, Sharatchandra and Gadgil 1975, Dinerstein 1980). However, formulating such estimates, for a deer that prefers dense habitats, has been difficult. In studies where animals cannot be directly viewed, or captured and tagged, the use of indirect population estimates has become prevalent. One of the techniques developed for deer study in North America that may prove applicable to the deer of Asia, such as the chital, is the pellet-group index (Neff 1968). If the rate of daily production of pellets is known, a systematic count of pellet-group accumulation per unit area can be translated into deer-days-use. The accuracy of this method rests on 3 basic assumptions. First, no pellet groups in the study area are overlooked during sampling. Second, pellet groups must remain in place during the sampling period. Third, the assumed daily defecation rate must closely approximate the species' actual defecation rate under the given habitat conditions. In a field study of chital in the Royal Karnali-Bardia Wildlife Reserve in Nepal, population estimates were made using several different count techniques (Dinerstein 1980). This multiple technique approach allowed comparisons between methods. Strip censusing by motor vehicle and sample area counts from tree platforms yielded similar chital population density estimates of 102.3 (SE = 11.9) and 97.0 deer/km2, respectively. Two years of sampling chital populations, supplemented by numerous foot transects through all habitats in the 11.8km2 study area, suggest that these density estimates approximate true deer densities. The density estimate derived from pellet-group counts in the same area, however, were almost 2.4 times higher than either the strip census or sample area counts. We believe that this large discrepancy stems from the use of an unsuitably low daily defecation rate estimate (13.0 pellet groups/deer/day) adopted from that frequently cited for wintering mule deer (Odocoileus hemionus) in North America (McCain 1948, Rogers et al. 1958, Smith 1964). To bring these pellet-group density estimates in line with the estimates from the other 2 sampling methods, however, we must assume a defecation rate of 24.0 pellet groups/deer/ day. A chital study under captive conditions, at the Woodland Park Zoological Gardens in Seattle, offered a unique opportunity to determine daily defecation rates for this tropical deer living on high quality forage. The primary objective of