Choice of census method
Table 9.1 lists the many methods that have been used for surveying birds. Though several methods
are listed, there are broadly two types: those for species that are evenly distributed across the
landscape; and those for species that are not (i.e. are highly clumped). Listing methods, territory
mapping, point counts and transects, for example, are best for species that are evenly distributed
(e.g. territorial species), whereas counts of colonies, roosts and flocks are best for species with
clumped distributions. Do bear in mind, however, that the dispersion of a species may vary
throughout the annual cycle. For example, seabirds often gather at breeding colonies in the spring,
but are out at sea for much of the rest of the year. In contrast, manywaterfowl are distributed widely
across the landscape while breeding, but commonly congregate outside the breeding season and
are then much easier to count. Different methods would thus be required for different seasons,
though it is often much simpler to count birds when they are clumped than it is when they are
dispersed.
Listing methods
The methods outlined in Table 9.1 also differ in their ability to provide absolute or relative
measures of abundance. Timed species counts and listing approaches, though efficient at providing
rapid inventories of the species in a particular area, will yield information only on the relative
abundance of species. Many of the other methods yield estimates of absolute abundance. Under
most circumstances, census methods that involve catching birds are not preferred; most bird
species are easier to see or hear than to catch, and catching involves extra investment in equipment
and training. Occasionally, however, this is not the case and capture may be the only practical
method.