There was no mystery regarding the death of a flock of birds in Romania last week—they were simply drunk, veterinarians said.

Residents of the Black Sea city of Constanta informed authorities on Saturday after they found dozens of dead starlings.

They feared another bird flu, which triggered mass deaths in avian populations in 2004-2006.

Tests on five birds showed gizzards full of grape marc, said Romeu Lazar, head of the city's veterinary authority, referring to a pulpy residue which is a by-product of winemaking.

Lazar explained that birds don't generally consume alcohol, but a harsh, snowy winter prevented the birds from finding food. If they been able to eat some seeds, this would have diluted the poison, Lazar said.

The grape marc was presumed to have come from a winery, but the veterinary chief did not know where.