A design-based strategy for estimating wildlife ungulate abundance in a\ud
Mediterranean protected area (Maremma Regional Park) is considered. The estimation\ud
is based on pellet group count (clearance count technique) in a set of plots, whose\ud
size and number is established on the basis of practical considerations and available\ud
resources. The sampling scheme involves a preliminary stratification and subsequent\ud
two-stage sampling. In the first stage, large strata (defined through habitat features) are\ud
partitioned into spatial units and a sample of units is selected by means of a sampling\ud
scheme ensuring inclusion probabilities proportional to unit size, but avoiding the\ud
selection of contiguous units. Then, the abundances of the selected units are estimated\ud
in a second stage, in which plots are located using a random scheme ensuring an even\ud
coverage of the units. In small strata, only the second stage is performed. Unbiased\ud
estimators of abundance and conservative estimators of their variances are derived for\ud
each strata and for the whole study area. The proposed strategy has been applied since\ud
the Summer of 2006 and the estimation results reveal substantial improvement with\ud
respect to the previous results obtained by means of an alternative strategy