In Boston, 47 grackles rained down from the sky above the Dorchester neighborhood last Thursday. 32 of the birds died at the scene or shortly after, and two cats that may have had contact with the birds also died. So far, the cause is unknown.

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Witnesses describe a chaotic scene, with birds attempting to fly from tree to tree and then weakly falling to the ground. The grackles, a type of songbird that travel in flocks, have been sent to Tufts University in order to determine the cause of death. Some potential possibilities include poisoning, a virus, or environmental pollution. Results are expected next week, but in the meantime, pet owners have been advised to keep their animals indoors.

Related: Study shows mass die-offs of birds, fish and marine invertebrates increasing

This isn’t the first time a mass bird die-off has spooked scientists. Earlier this year, thousands of dead birds washed up on Alaska’s coast – the birds were thought to have starved to death due to climate change disrupting their food supplies. In fact, a 2015 study found that mass die-off events involving birds, fish, and marine invertebrates had increased in number and magnitude over the past 70 years.

Via The Guardian

Images via Phillip Cowan and Ken Gibson