| Summary: | An unprecedented wreck of razorbills (Alca torda) occurred along the Mediterranean Sea during winter 2022-2023. To determine the potential causes of death and origin of these birds, 46 dead razorbills collected on the coast of Malaga (Spain) were analysed. Necropsies revealed poor body 0condition and starvation signs in most birds. Influenza virus was excluded through PCR testing. However, a high prevalence (58%) of gastrointestinal nematodes was found, primarily Contracaecum variegatum, associated with oesophageal and proventricular ulcers in 60% of razorbills. Stable isotope analysis of feathers showed that most of the birds likely were from North Sea colonies, although 33% of the individuals presumably were from other breeding locations. Persistent Atlantic storms likely triggered this wreck by impeding foraging and forcing migration of weakened razorbills. Although starvation induced by harsh weather seemed to be the primary cause of mortality, the high parasite loads and associated digestive ulcers found in most razorbills may have acted synergistically to further weaken these already emaciated birds. The interplay of these factors offers a better understanding of the multifaceted drivers of mass seabird wreck events.
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