Growing mortality rates among Northern Gannets entering wildlife rehabilitation: the challenge in diagnosing aspergillosis as the underlying cause

Since 1988, the Northern Gannet Morus bassanus (hereafter ‘Gannet’) population has exhibited an extremely low and downward trending release rate when admitted to wildlife rehabilitation facilities in the United States. Across more than 4,000 Gannets admitted to rehabilitation facilities between 1988 and 2023, patients demonstrated an overall release rate of 13.7%. More concerning is that Gannet release rates have not exceeded 10% since 2018 and dropped to 5.5% in 2019. The challenge is that Gannets admitted to rehabilitation facilities often exhibit no external signs of injury making it difficult for rehabilitators to diagnose their reason for admission. However, they are frequently in such poor body condition that they require immediate euthanasia or die within 24 hours of admission. In many instances, their clinical signs are listed as exhaustion, trauma, or emaciation. Based on data collected from 39 rehabilitation facilities along the East Coast of the United States and one facility in Canada, 46.4% of patients were admitted due to exhaustion or emaciation. To determine cause of death with more accuracy, more than 90 Gannet patients (2.2%) were necropsied. The results indicated that over 60% of the necropsied patients were suffering from aspergillosis.