Methylxanthine Exposure in the American White Ibis ( Eudocimus albus) in Florida, USA

Naturally occurring methylxanthines (MTXs) are plant-derived alkaloids, including caffeine, theobromine, and theophylline. Common sources of these compounds are coffee, chocolate, and tea. Methylxanthine toxicosis has been frequently described in domestic dogs and pet birds, but few reports exist for free-ranging wildlife species. From November 2019 through November 2020, we evaluated 24 American White Ibis (Eudocimus albus) and one Yellow-crowned Night Heron (Nyctanassa violacea) collected from morbidity and mortality events along the Atlantic coast of Florida, USA. Live ibises displayed clinical signs of lethargy, ataxia, and recumbency before their euthanasia. Toxicologic assays performed on liver primarily revealed caffeine and theobromine, with few detections of theophylline. Histologic findings were nonspecific and included diffuse vascular congestion in multiple tissues. We were unable to identify the source of MTX exposure in the clustered ibis mortality events, but several cultivated botanical sources (e.g., native Yaupon holly [Ilex vomitoria]) of MTX grow on Florida's landscape. Additionally, caffeine is a ubiquitous environmental pollutant of both freshwater and marine ecosystems, with anthropogenic inputs from sewage effluent and improper disposal of pharmaceutical products and manufacturers' waste. Our findings underscore the need for broad consideration of the ecotoxicologic impacts of caffeine and related chemicals on free-ranging wildlife species.