Methods for measuring populations of small, diurnal forest birds.

Abstract

Before a bird population is measured, the objectives of the study should be clearly defined. Important factors to be considered in designing a study are study site selection, plot size or transect length, distance between sampling points, duration of counts, and frequency and timing of sampling. Qualified field personnel are especially important. Assumptions applying to all bird-counting techniques are discussed. The following techniques and their applications are discussed; simple line transect, fixed-width transect, variable-width transect, simple point count, fixed-radius point count, variable-radius circular plot, spot mapping, and total mapping. For determining species richness and presence, the simple line transect and simple point count methods are recommended. Measures of relative abundance can be obtained by using the simple line transect, simple point count, fixed-width line transect, and fixed-radius point count methods. Population trends during the same season each year can be detected by using the same trends as those used for relative abundance. If more than one season is involved, however, the variable-distance transect or variable-radius point count are necessary to account for differences in bird detectability. Habitat-use patterns can be determined best by using the spot-map method to elucidate territory locations. More precise information can be obtained for larger birds by using radio transmitters.