How many birds breed in Switzerland? An overview of the methods applied for estimating population sizes

We used data from different sources, developed and applied several estimation methods, and confronted the resulting estimates with species experts to achieve breeding size population estimates for all bird species currently breeding in Switzerland.

Population size estimates of birds have a wide range of practical conservation uses. As part of the Swiss Breeding Bird Atlas 2013–2016, we aimed to update the national breeding population size estimates for all species.

For very rare species and for rare colonial breeders, the estimates are complete enumerations based on annual compilations of all breeding records. For the other species, we applied extrapolation methods of varying complexity, either based on the data from the 2318 one-kilometre squares where territory mapping for the breeding bird atlas was conducted, or based on all breeding period records from 2013 to 2016. In some cases, these data were combined with regional population estimates. For most species, we considered the results of several different approaches to determine the final estimate. Here, we give an overview of the applied procedures, along with some examples. We provide access to code that allows the reproduction of our analyses.

We present population size estimates for all 210 species and 4 subspecies of birds breeding in Switzerland. The total population size of all Swiss breeding birds amounts to just over ten million breeding pairs. The largest share consists of species with forest as their main habitat.

A main challenge was to decide species by species which approaches lead to the most reliable results. The application of a rule-based selection approach alone is dangerous. Comparing the outcome of different approaches and involvement of species experts are crucial steps to getting sound population size estimates.