Filling the gaps: Using count survey data to predict bird density distribution patterns and estimate population sizes

Birds play an increasingly prominent role in politics, nature conservation and nature management. As a consequence, up-to-date and reliable spatial estimates of bird distributions over large areas are in high demand. The requested bird distribution maps are however not easily obtained. Intensive fieldwork over a spatially dense observation network requires a large effort by hundreds or thousands of volunteers, and is only feasible once in every few decades. Therefore, to create distribution and abundance maps at shorter time intervals of years or even months, monitoring data has to be used. However, monitoring data typically come from a spatially less dense observation network. In order to produce reliable distribution maps with these data, additional biological knowledge and relatively complex statistical procedures have to be used. This study explains the several steps and issues involved via a case study where distribution maps of the Common Buzzard are constructed for The Netherlands