Counting seabirds

Counting birds at sea requires a lot of knowledge and experience. For decades, our bird counts have provided insight into possible effects of natural changes or human activity on seabird populations, such as the construction of offshore wind farms.

Using seabird counts, unique areas can be mapped. By storing all the count data in the international European Seabirds At Sea (ESAS) database, long-term data series are created which allow a comparison with other years and counts.

Counting seabirds is work for seasoned birdwatchers: they know every species, every plumage and moult, every sound, the behaviour and also every bird that is not a seabird. Cetaceans are also counted. This is done from a mobile counting platform that can be mounted on various ships.

Wageningen Marine Research has a pool of researchers who work according to standardised ESAS (European Seabirds At Sea) protocols. That requires a lot of precision. Every bird that swims within a 300 m wide strip alongside the ship is counted. Swimming birds are always counted per five minutes of sailing time. Birds flying over the transect are only counted on the whole minutes of a count, and only within 300m sideways and forwards, to avoid overestimating densities. Bird behaviour (foraging, swimming, moulting) is recorded according to standard codes. All data are entered into the ESAS database and a cruise report is made for each survey.

Modelled maps

Based on the observations, modelled distribution maps are made, for which various techniques are available. The models take into account weather conditions and other factors that influence the observations.


Seabird counts are used to measure the effects on seabirds of large industrial projects such as offshore wind farms. We also map special ecological areas for nature policy (Natura 2000, Marine Framework Directive).

Quality assurance

Our bird observers are trained in the application of ESAS protocols and also give training themselves. Their thorough knowledge of the ecology contributes to a responsible interpretation of the data. Our working area is not only the North Sea, but also the Caribbean Netherlands and the Antarctic. Wageningen Marine Research contributes with its seabird observations to the international ESAS database and has extensive experience in modelling bird distributions and various statistical techniques such as GLM and GAM models, Linear mixed effects modelling, Bayesian statistics, Spatial modelling with Integrated Nested Laplace approximation, Model-based Geo-statistics, Cartographic Design for Wildlife Professional and R (statistical computing).