bizarre spate of young blackbird deaths at a school in England was likely caused by the feathered teens getting drunk on fermented berries, crashing mid-air and falling from the sky, according to vets.

Police and animal experts were called in after more than a dozen birds were found dead at a primary school in Cumbria last August -- many of them sporting serious injuries.

One of the juvenile blackbirds was found alive but appeared "drunk", pressing its wings into the ground to steady itself and trying to stay upright by leaning against the walls of the enclosure it was taken to.

Foul play was initially suspected, but post-mortem examinations ruled out a murder spree or diseases like bird flu.

Instead, the examiners found berries in the birds' stomachs that had a smell of fermentation, said a report in the BMJ Group journal Veterinary Record.

Further toxicological test found high levels of pure alcohol or ethanol in the liver of one of the birds.

"Some of the birds had died from traumatic injury, possibly related to in-flight collisions secondary to intoxication," wrote investigators from the Animal Health and Veterinary Laboratories Agency.

"Unsteadiness on the feet, a tendency to fall over and losing the ability to steer is considerably more of a problem when life is normally spent in trees or in the air," added a media statement.

The lone survivor made a full recovery and was released back into the wild after sleeping off its hangover.