Toxins and Disease Kill Millions of Seabirds

Biotoxin poisoning is the leading cause of mortality among seabirds in the United States, killing tens of thousands every year.

An assessment of 630,000 dead birds finds that over half succumbed after acquiring botulism from ingesting lethal Clostridium botulinum bacteria.

The toxin mainly affected birds that live near coastlines or that frequent both marine and freshwater habitat.

Diseases, both viral and bacterial, are the second most prevalent cause of death, accounting for 20 percent of the mortality among birds that died between 1971 and 2005. Infected birds were most often diagnosed with avian cholera, paramyxovirus, West Nile virus and salmonellosis. Both biotoxin poisoning and infectious diseases became more prevalent among seabirds over the 34-year period.

According to the authors of this study, their results indicate that botulinum toxin and infectious diseases in three decades have killed over five million aquatic birds in the US.

In contrast, all but a few birds inhabiting the open ocean stay free of biotoxin and disease. Instead, three-quarters of their deaths are attributed to starvation. Emaciated birds have become more common in recent years. This trend corresponds with declines of marine life observed in other research. Oil spills contributed to another 11 percent of the mortality found among open-ocean birds.

Less common were deaths in seabirds from severe weather, heavy metals, pesticides and collisions with powerlines. Other birds died from causes that researchers didn't investigate in this study, notably fishing net entanglements and algal bloom toxicity.

Altogether 158 bird species from 23 taxonomic families were examined. The highest losses occurred among herons, gulls and wading birds such as sandpipers.