Manx Shearwaters Puffinus puffinus, like other procellariiform seabirds, spend most of their lives at sea and are encountered on land only when breeding at colonies or if they are grounded due to unfavourable weather conditions or exposure to artificial light. Here, we used historical ringing data to explore the age class structure and spatial patterns of Manx Shearwater groundings and examined ringing and recovery data to identify records of post-grounding survival for first-year and adult birds. We noted 35 cases, out of 6,381 ringed grounded shearwaters, where a bird went on to be recaptured, including two individuals that were later recorded as having successful breeding attempts. While this constitutes only a small number of birds confirmed to have survived following grounding, it is likely to be a considerable underestimate of survival considering the low probability of recapturing a surviving shearwater. Finally, we found that a greater proportion of grounded birds were first-years compared to adult shearwaters, and that adults were found to be grounded further away from colonies than first-year birds. This may be indicative of differential impacts of light pollution at different life stages.

Procellariiform seabirds are one of the most threatened groups of birds. Major threats include invasive species, bycatch in fisheries, hunting and climate change (Dias et al. 2019). They spend most of their life at sea and, under normal circumstances, come to land only to breed at colonies located around coastlines or on offshore or oceanic islands (Warham 1990). Procellariiformes are, however, sometimes encountered on land away from their colonies after grounding, perhaps in association with light pollution, oil spills or unfavourable weather conditions such as storms (Telfer et al. 1987; Camphuysen et al. 1999, 2002; Rodríguez et al. 2017a). These ‘groundings’ peak shortly after the fledging period, when mostly juvenile shearwaters can become stranded in artificially lit towns, cities, ships and oil platforms near their nesting sites (Rodríguez et al. 2017a). In response, conservation organisations and local volunteers may deploy personnel to rescue, ring and release grounded shearwaters close to large colonies (e.g. Le Corre et al. 2002; Day et al. 2003; Rodríguez et al. 2017b).

Efforts have been made to monitor the body condition of grounded seabirds (Rodríguez et al. 2017b; Cuesta-García et al. 2022), as higher weight is an indication of higher probability of survival for juvenile seabirds (Perrins et al. 1973; Becker & Bradley 2007; Maness & Anderson 2013). For example, a study comparing the weight of juvenile Short-tailed Shearwaters Puffinus tenuirostris recovered at different locations indicated that birds grounded due to light pollution had lower body weights compared to near-fledging birds at the colony, while water-logged fledglings found washed up on beaches were in the poorest condition of the three groups (Rodríguez et al. 2017b). Whilst considerable effort is put into understanding the consequences of seabird grounding, little is known about survival to breeding age of rescued fledglings, which is important for estimating the impact of grounding casualties on seabird populations (Simons 1984; Fontaine et al. 2011; Griesemer & Holmes 2011; Gineste et al. 2017).

Our study species, the Manx Shearwater P. puffinus, breeds mainly on three islands in Great Britain (Fig. 1A). While the species’ total population is estimated at 1.03–1.18 million individuals (Birdlife International 2015), a combination of hard-to-access breeding areas as well as nests located in burrow chambers, makes it difficult to accurately estimate the population size or its trend (Perrins et al. 2018). Like other procellariiform seabirds, Manx Shearwaters are affected by light pollution and unfavourable weather conditions, with grounding being reported mainly near colonies (Rodríguez et al. 2008; Miles et al. 2010; Syposz et al. 2018). Existing studies of grounding impacts, however, have mainly focused on a single location, failing to report the events at a larger scale.

Here, using ringing and recovery data, we investigated the age class structure and spatial distribution of Manx Shearwater groundings around Britain and Ireland, as well as records of confirmed survival of individuals following rescue. Adult Procellariiformes are thought to be less susceptible than juveniles to grounding caused by light pollution (Camphuysen et al. 1999; Troy et al. 2013; Rodríguez et al. 2015; Syposz et al. 2018), thus we expected to find differences in the frequency and distribution of grounding events depending on age class. Furthermore, survival rates of adult procellariform seabirds are higher than those of fledging juveniles (Perrins et al. 1973; Simons 1984; Jenouvrier et al. 2008), thus we expected that the probability of recapture after an initial grounding event would be higher in adults than juveniles.

We thank the BTO Ringing Scheme for providing data from historically ringed and re-trapped Manx Shearwaters. The BTO Ringing Scheme is funded by a partnership of the British Trust for Ornithology, the Joint Nature Conservation Committee (on behalf of Natural England, Natural Resources Wales, NatureScot and the Department of Agriculture, Environment & Rural Affairs, (Northern Ireland)), the National Parks and Wildlife Service (Ireland) and the ringers themselves. We would like to also thank The Wildlife Trust of South and West Wales, Bardsey Bird Observatory, Copeland Bird Observatory and Edward Grey Institute (EGI). Special thanks go to Steve Sutcliff and John Hayes for rescuing birds from the refinery, as well as other volunteers and ringers that contributed to the rescue efforts. We also thank Skokholm Bird Observatory for providing data on re-trapped birds and Prof. Tim Guilford, Dr Natasha Gillies and two anonymous referees for useful feedback on this manuscript. OP was supported by a Junior Research Fellowship at St John’s College, Oxford.

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