Bats regularly migrate over the North Sea, but information on the environmental conditions when this occurs is scarce. Detailed information is urgently needed on the conditions under which bats can be expected offshore, as the number of offshore windfarms that can cause fatalities amongst bats in the North Sea is increasing rapidly. We performed ultrasonic acoustic monitoring at multiple nearshore locations at sea between 2012 and 2016 for, in total, 480 monitoring nights. We modelled the offshore occurrence of Nathusius’ pipistrelle in autumn as a function of weather conditions, seasonality, and the lunar cycle using a generalized additive mixed model (GAMM). We investigated which covariates are important using backward selection based on a likelihood ratio test. Our model showed that important explanatory variables for the offshore occurrence of Nathusius’ pipistrelle are seasonality (night in year), wind speed, wind direction, and temperature. The species’ migration is strongest in early September, with east-northeasterly tailwinds, wind speeds < 5 m/s, and temperatures > 15 °C. Lunar cycle, cloud cover, atmospheric pressure, atmospheric pressure change, rain, and visibility were excluded during the model selection. These results provide valuable input to reduce bat fatalities in offshore wind farms by taking mitigation measures.

Harbour porpoises (Phocoena phocoena) are regularly monitored to assess how they are impacted by the construction and operation of offshore wind farms. A suitable method to do this is passive acoustic monitoring (PAM) by stationary hydrophones, for example CPODs. These devices provide information on echolocation click activity, which can then be analysed. Prey occurrence is considered one of the main drivers in porpoise distribution and successful feeding is vital to the fitness and survival of individual porpoises. Information on foraging behavior, however, is difficult to obtain in the field, in particular as animals feed under water. Harbour porpoise use narrow band high frequency signals in a sequence of clicks (called click trains) for echolocation, communication and foraging. The different behaviors are characterised by the modulation in time lag between clicks (inter-click interval). Using CPOD data collected in Dutch water during and after pile driving noise exposure, the present study first investigated different data processing methods for the quantification of foraging behavior. The results indicate that: (1) a click-based classification provides the best results (as opposed to using click trains), (2) foraging events could be detected in sufficient numbers to reveal patterns over time, such as correlation with pile driving activities.

The avifauna of the Dutch Caribbean island of St. Eustatius has been little studied. We document 22 new bird species for the island and update the status of several important species based on our recent observations. The documented avifauna of the island amounts to 75 published species records. We conclude by pointing out several positive developments in the avifauna and ascribe these to the combined effects of reduced hunting, the legal establishment of protected park areas, and a growing environmental awareness among the island’s inhabitants. Keywords: avifauna, Dutch Caribbean, Netherlands Antilles, St. Eustatius Resumen: La avifauna de la isla San Eustaquio de las Antillas Holandesas ha sido poco estudiada. Basados en nuestras recientes observaciones documentamos 22 nuevas especies de aves para la isla y actualizamos el estado de muchas especies importantes. La avifauna documentada de la isla asciende a 75 registros publicados. Concluimos destacando que hay muchos avances positivos para la avifauna y que se pueden atribuir a los efectos combinados de la reducción de la caza, el establecimiento legal de áreas protegidas y el creciente interés medio ambiental entre los habitantes de la isla. Palabras clave: Antillas Holandesas, avifauna, San Eustaquio Résumé: L’avifaune de l'île caribéenne de Saint-Eustache dans les Antilles néerlandaises a été peu étudiée jusqu’à présent. Nous mentionnons ici vingt-deux nouvelles espèces pour l'île, et actualisons le statut de plusieurs espèces importantes, sur la base de nos observations récentes. L'avifaune de l'île compte 75 espèces faisant l’objet de mentions publiées. Nous concluons en soulignant plusieurs évolutions positives pour l'avifaune pouvant être attribuées aux effets combinés de la pression de chasse réduite, de la désignation de zones protégées et de la prise de conscience croissante des habitants de l'île vis-à-vis de l'environnement. Mots clés: Antilles néerlandaises, avifaune, Saint-Eustache

The harbour porpoise (Phocoena phocoena) is considered part of the ‘Outstanding Universal Value’ characterising the Wadden Sea World Heritage Site (WS WHS). The Trilateral Wadden Sea Plan aims to preserve the conservation status of the Trilateral Wadden Sea Cooperation Area, encompassing the WS WHS. The plan has specified two conservation targets for the harbour porpoise: (1) viable stocks and a natural reproduction capacity and (2) conservation of habitat quality for its conservation. To assess the current occurrence of the harbour porpoise in the Wadden Sea area, we collated and analysed data from regional and national research projects using telemetry, aerial surveys, strandings and passive acoustic monitoring, obtained over the years 1990–2020. The results illustrate that porpoises occur in both offshore and intertidal waters, showing seasonal movements and changes in local occurrence over time. Some porpoises displayed limited home ranges throughout the year, suggesting a possible residency for some of the animals using the Wadden Sea area. We also showed that methods, frequency and spatial coverage of monitoring activities vary among the countries Denmark, Germany and the Netherlands. We discuss the suitability of the different methods both regarding the challenges of monitoring in the complex Wadden Sea habitat as well as their ability to target the conservation aims of the WHS. We give several recommendations to assess the status of the species to meet the identified conservation aims.