Counting seabirds at sea

Seabird surveys help to identify special areas. By storing all count data in the international European Seabirds at Sea (ESAS) database, long-term data series are created that allow comparison between years and surveys.

How does the counting of seabirds take place?

Counting seabirds is a task for seasoned birdwatchers: they know every species, every plumage and moult stage, every sound, and behaviour, as well as every bird that is not a seabird. Marine mammals are also recorded. Counts are conducted from a mobile survey platform that can be mounted on various vessels.

We have a pool of researchers who work according to standardised ESAS (European Seabirds at Sea) protocols. This must be done accurately. Every bird swimming within a 300-metre-wide transect alongside the vessel is counted. Swimming birds are recorded every five minutes of travel time. Birds flying over the transect are only counted on the whole minutes of a survey, and only within 300 metres laterally and forward, to avoid overestimating densities. Bird behaviour (foraging, swimming, moulting) is recorded using standard codes. All data are stored in the ESAS database.

Modelled maps

Based on the observations, modelled distribution maps are produced using various techniques. The models take into account weather conditions and other factors that may influence the observations.

Applications

Seabird surveys are used to assess the effects of large industrial projects, such as offshore wind farms, on seabirds. They are also used to identify important ecological areas for conservation policy (Natura 2000, Marine Strategy Framework Directive).

Quality assurance

Our bird observers are trained in applying ESAS protocols and also provide training themselves. Their thorough knowledge of ecology contributes to a sound interpretation of the data. Our working area includes not only the North Sea but also the Caribbean Netherlands and the polar regions of both hemispheres. 

We contribute our seabird observations to the international ESAS database. In addition, we have extensive experience in modelling bird distribution and applying various statistical techniques, including GLM and GAM models, linear mixed-effects models, Bayesian statistics, spatial modelling (INLA and model-based geostatistics), cartographic design, and R (statistical computing).