Last summer, British veterinary officials were called to a primary school in Cumbria, England, to solve the mystery of a dozen young blackbirds that were found dead, many with clear physical injuries.
Tests ruled out lethal infections, such as avian flu, and showed that the birds generally had been in good health before their premature death. But at the scene, the researchers recovered a live bird that was acting strangely. It was unsteady on its feet, it had to bring its wings to the ground to support itself, and it leaned against the walls of its enclosure at a wildlife rescue center. In short, the bird seemed drunk.
The researchers also discovered that all the dead birds had one thing in common: berries found in their guts that smelled fermented, suggesting the victims died from flying while intoxicated.
Besides the wobbly bird that appeared drunk (and recovered after two days), a few more live blackbirds had been spotted at the school hanging out on rowan trees, which produce berries that are not usually poisonous to birds. Some berries on the ground, however, looked damaged, meaning the fruits could have been susceptible to yeast infestation, which would have sped up fermentation and made the berries alcoholic.
A toxicological analysis of three tissue samples from the dead birds revealed one had high levels of pure alcohol, or ethanol. The authors are not sure why only one of the samples came back positive and say they cannot prove the birds died after consuming too much alcohol. They nonetheless suspect the birds had become intoxicated on fermented rowan berries, and some likely died of injuries sustained in mid-air collisions.
The researchers, who detailed their investigation in the journal Veterinary Record, note a 1999 case reached a similar conclusion about redwings seen tumbling out of holly trees. Those birds did not have any hazardous chemicals in their bodies, but holly berries were found in their guts and tissue samples contained high levels of alcohol.