Generating population estimates for common and widespread breeding birds in Ireland

Abstract

Capsule Population estimates for 51 common breeding birds, totalling 62 million individuals, were estimated for Ireland.Aims To generate robust population estimates for common and widespread breeding birds across Ireland.Methods Densities were generated for common breeding birds using data from annual bird monitoring surveys using count data for all years between 2006 and 2010 inclusive. Bird atlas data were then used to (1) quantify the distribution of each species (10-km squares), and (2) generate an estimate of proportion occurrence of each species within each square. The total number of birds of each species was generated by multiplying proportion occupancy by the total area of the 10-km square and by the mean regional density generated from the bird monitoring data, and by summing the estimates of squares.Results Almost 62 million individuals of 51 common breeding birds were estimated. Wren Troglodytes troglodytes, with an estimate of more than 6 million individuals, contributed 10% of the total birds recorded. Swallow Hirundo rustica and Robin Erithacus rubecula were the next most numerous, at 5.8 and 5.4 million individuals. A total of 15 species were estimated at more than one million individuals each.Conclusion The estimates of detected individuals generated are based on best available information and analyses to date. Incorporating the bird atlas data permits vastly improved estimates by providing better informed distribution range across which the regional densities were extrapolated. However, estimation of densities and population sizes based on data from annual monitoring surveys alone is limited to species with widespread distributions because of the relatively low coverage and limited detectability of scarce species by this methodology.