It was a mass die-off of tufted puffins that had scientists looking for answers. It happened in 2016 and researchers have come up with some answers.

When the first birds showed up dead or dying, there was speculation whether large storms, crashing waves and high winds may have played a part, but this event goes beyond mere weather.

Scientists say a climate breakdown contributed to birds' demise. Carcasses washed up on the Pribilof island of Saint Paul and were collected for study. It is estimated that between 3,150 to 8,500 birds died.

It seemed that the puffins had become the latest species to experience a mass-mortality event—a large-scale die-off, of a kind that's becoming more and more common.

The birds rely on pollack, cod and other fish in the cold pool of the Bering Sea. When that cold pool doesn't form and the fish go elsewhere, the birds suffer. The sea itself is seeing rising temperatures, contributing to the decline of sea ice, which also threatens more species than just the tufted puffin.