Stable isotopes reveal the importance of seabirds and marine foods in the diet of St Kilda field mice

Introduced mammals have devastated island nesting seabird populations worldwide. Declines in breeding seabirds on St Kilda, UK, have been linked to climate change and predation from great skuas Stercorarius skuas, but the introduced St Kilda field mouse Apodemus sylvaticus hirtensis may also play a role by feeding on adults, chicks or eggs. Here, we use stable isotopes in St Kilda mouse blood and potential dietary items to investigate their foraging ecology, specifically focussing on the importance of seabirds and marine foods in their diet. Mice were seasonally sampled at three sites on Hirta, St Kilda over three consecutive years (2010–2012). The δ13C and δ15N ratios were used in analyses, including isotope niche and dietary source mixing models, to examine foraging behaviour among locations and between seabird breeding seasons. Mice sampled in Carn Mor – where the majority of the island’s seabirds nest - had consistently higher δ13C than other locations throughout the year, with δ15N also being significantly higher for all but one comparison. The isotopic niche width (SEAs) of Carn Mor mice in each season were distinct from the other locations, and became smaller during the seabird breeding season. Dietary mixing models revealed that seabirds made up a large proportion of the diet for mice from Carn Mor, particularly during the seabird breeding season. In conclusion, our work reveals that seabird-derived foods are likely to form a significant part of the diet of St Kilda mice populations located in and around breeding colonies. It is unclear however, whether this is from scavenging or predation of seabirds, or through their discarded food items. Given that mice have had significant effects on seabird populations elsewhere, it is important to carry out further work to determine whether mice are a significant cause of seabird mortality in this island ecosystem

Market surveys and social media provide confirmation of the endangered giant freshwater whipray Urogymnus polylepis in Myanmar

The giant freshwater whipray Urogymnus polylepis is a threatened species that is vulnerable to riverine and coastal marine pressures. Despite its threatened status, the range of U. polylepis is still being determined. In this study, photographic evidence of U. polylepis in Myanmar was provided through market surveys (2017-2018) and social media (Sharks and Rays of Rakhine Facebook page, 2021). Urogymnus polylepis is exposed to fisheries and habitat degradation pressures in Myanmar; therefore, conservation management is likely needed to ensure populations persist into the future

GPS tracking reveals rafting behaviour of Northern Gannets (Morus bassanus): implications for foraging ecology and conservation

Capsule Three quarters of tracked Northern Gannets (Morus bassanus) at Grassholm gathered in rafts around the colony, concentrated within a recently designated at-sea Special Protection Area (SPA), but rafting was not correlated with foraging effort. Aims To investigate the incidence, distribution and foraging implications of Northern Gannet rafting behaviour in waters adjacent to a large colony. Methods Using bird-borne global positioning system (GPS) loggers we reconstructed at-sea movement and used a speed filter to identify rafting behaviour within 10 km of the colony. We mapped the spatial distribution of rafting events from 160 breeding individuals over 5 years, and investigated the relationship between foraging effort (trip duration and total distance travelled) and the presence/absence of rafting. Results On average, 74% of tracked birds engaged in rafting. Of the 381 foraging trips analysed, rafting was recorded on 237 (62%). Birds were more likely to raft on outbound (224 trips, 59%), than inbound journeys (38 trips, 10%). Presence/absence of rafting did not correlate significantly with foraging trip distance or duration nor with duration of nest attendance. The majority of rafting was concentrated in a 2-km radius around the colony within a recently designated seaward SPA extension. Birds showed low individual repeatability in rafting, although there was lower variation within, than among, individuals. Conclusion Our results show that rafting is important for breeding gannets on Grassholm, and a recently designated at-sea SPA encapsulates the core distribution of rafting. Rafting did not appear to be correlated with foraging behaviour. Given the dearth of literature on rafting and the wealth of GPS tracking data for seabirds, we suggest that similar research be conducted elsewhere to further elucidate the ecological and applied significance of this behaviour

Sexual segregation of gannet foraging over 11 years: movements vary but isotopic differences remain stable

Acknowledgements. Research was funded by the Natural Environment Research Council (GW4+ Doctoral Training Partnership studentship to B.L.C. [NE/L002434/1]; Standard grant to K.C.H., S.B. and S.C.V. [NE/H007466/1]; and New Investigators grant to S.C.V. [NE/G001014/1]), and the Euro- pean Union (Interreg CHARM III). We thank the Royal Society for the Protection of Birds for permission to work on Grass- holm. We thank Toby Doyle, David Pascall and Lena Wilfert for assistance in molecular sexing, and David Pascall for analytical advice. We thank Richard Phillips and Brendan Godley for comments on the manuscript. Satellite products were ac- quired and processed by the Natural Environment Research Council Earth Observation Data Acquisition and Analysis Service (NEODAAS). We thank Matthew Witt for help in accessing vessel activity data. Many people helped with field- work, including Tim Guilford, Claudia Stauss, Sylvie Vandana- beele, Nicola Childs, Pearl Costello, Rocio Moreno, Matthew Gummery, Lisa Sztukowski, Jana Jeglinski, Matthew Carter, Matthew Nicholson, Dimas Gianuca, Rhiannon Meier, Laura Zango, Kirsten Archibald, Jacob Gonzalez-Solis, Jen Tyler, Tommy Clay, Calum Laver, Melanie Wells, Zoe Deakin, Zoe Courchene, Richard Phillips, John Arnould, Emma Dwan, Jack Wright, Georgia Bardua, Paulo Catry, Sarah Parmor and Megan Francis. We thank the editor Kyle Elliott and 3 anony- mous reviewers for helping us to improve the manuscript. The GPS data are stored on the BirdLife International Sea- bird Tracking Database (www.seabirdtracking.org).Peer reviewedPublisher PD