Temporal variation in tiger (Panthera Tigris) populations and its implications for monitoring

Tigers (Panthera tigris) are endangered wild felids whose elusive nature and naturally low densities make them notoriously difficult to count. We present 7 years of camera trapping, tracking, and observational data on a local tiger population in Chitwan National Park, Nepal, to quantify changes in abundance of demographic groups and to identify underlying causes. Mean abundance in the 100-km² study area was 18 tigers, but there was high variance among years. Transients were generally recorded at low levels, but there were large oscillations in numbers of tiger offspring, driven by infanticide perpetrated by male tigers taking over territories. The number of breeding animals in the study area remained relatively stable, with about 6 breeding females and 1 or 2 breeding males. The high density of breeding adults in Chitwan National Park highlights the region as a potential stronghold for tigers. Concentrating on counting breeding animals increases the power of monitoring programs to detect change over time. An alternative approach is to carry out surveys on a scale large enough to encompass sufficient territories to compensate for the local impacts of periodic turnover of adult males on total abundance.