Beached bird surveys in The Netherlands : summer 2025 & winter 2025/26 : a step back...

This is the annual report on beached bird survey (BBS) combining results obtained
in The Netherlands during summer 2025 (May-Oct) and the winter 2025/26 (Nov-Apr). While the long term study showed a steady, promising, long-term decline in oil pollution rates among guillemots, accelerating since 2005, a serious oil incident in autumn 2025 reminded us again of the recent past. While almost all recent seasons have shown exceptionally low oil rates, two pollution incidents occurred in the winter of 2024/25, resulting in an overall oil rate of 5.8% (n = 86) among guillemots, the highest value since 2017/18. With this new spill, in autumn 2025, even though it must have been only one isolated incident (likely an oil discharge), it is clear that oil pollution is not completely gone as yet, and could even return. With an oil rate of 12.5% (n= 183), the multi-year average doubled, to reach 4.0 ± 5.3%, which is only just within the OSPAR targets set for 2030. This increase is despite extra-mortality in Common Guillemots caused by a wreck (starvation induced mortality) that occurred simultaneously, and it should be noted that the incident occurred in Oct-Nov whereas the standard monitoring period for OSPAR is winter (defined as Nov-Apr). Calculated over the relevant period (i.e. Oct-Nov 2025), species-specific oil rates were alarmingly higher: 23.8% in Common Guillemots (n= 231), and even 68.0% in Razorbills (n=50), and these results are therefore presented separately within this report.