How relevant are estimates of national bird population sizes in the Czech Republic? Comparison between atlas data and estimates based on point counts not adjusted for unequal species detectability
Abstract
Estimates of total population sizes of individual bird species are widely used in macroecology and conservation biology. Current estimates of population sizes of Czech birds are based on atlas mapping data.
However, this mapping has primarily been focused on breeding bird distribution and not on species abundance. The aim of our study is to compare these atlas-based estimates with extrapolations from point count data.
For this purpose, we collected data on breeding bird abundances not adjusted for species detectability, counted along a 400-km point count transect. The atlas estimates were strongly correlated with transect estimates suggesting that the assessment of species relative commonness and rarity is quite independent of the method of the estimate.
Although the total estimate of the number of all individuals for all species together was similar using both types of data, the atlas estimates of species population sizes were lower than the transect-based ones in most but the commonest species. Unfortunately, we cannot judge which kind of data is closer to reality.
Since the estimates often differed by an order of magnitude for a given species, it is possible that both of them are substantially biased. We urge to focus on achieving more reliable estimates using modern bird census techniques employing representative sampling and quantification of species detectability.