Some alarming news surfaced in Canada last week, when more than 50 black birds suddenly dropped dead out of the sky over Winnipeg, Manitoba, on August 7th, according to the CBC. The birds, which were later confirmed to be grackles, reportedly began flocking together by the thousands over cars and buildings in the city's north end. Frightened residents reported seeing the birds acting "dizzy" before abruptly plummeting out of the sky, as the CBC reported. At least 11 birds were found on the ground alive and taken in by the Winnipeg Humane Society, but they too couldn't stand or fly and were later euthanized.

For now, the mass grackle deaths remain a mystery. As a Manitoba provincial spokesperson explained in a statement to The Verge:

Preliminary test results have eliminated West Nile virus, avian influenza or Newcastle disease as the cause of death for a number of grackles in Winnipeg last week. Testing is ongoing, and Manitoba Conservation and Water Stewardship will provide updated information as it is received.

Mass bird deaths, while decidedly not common, have occurred in other parts of the world in recent years, drawing alarm from locals and conspiracy forums online. An estimated 5,000 birds of varying species, including grackles, plummeted to their deaths over Beebe, Arkansas in the US on New Year's Eve 2011. While the cause of death was officially ruled blunt force trauma, wildlife investigators later speculated that fireworks in the sky may have forced the birds to fly lower than normal, causing them to crash into objects. When 300 birds were found dead later that month near Yankton, South Dakota, the likeliest cause was reported to be a bird-killing poison used by the US Department of Agriculture specifically to try and stop birds from defecating in livestock feedlots. It's too soon to say whether any similar instances played a role in the death of the grackles over Manitoba, but we'll update once we hear back from the Manitoba government.