ANCHORAGE, Alaska (AP) — Pacific Ocean seabird experts continue to study a massive die-off of common murres that occurred a year ago but say most evidence points to a climate event that warmed waters of the North Pacific.

Federal officials recorded 6,000 dead common murres in California, Oregon and Washington and 46,000 in Alaska in 2015 and early 2016.

U.S. Geological Survey research wildlife biologist John Piatt says the mortality conservatively reached 500,000 birds because most dead birds wouldn't have washed to shore.

The birds were emaciated. Piatt says the deaths likely were multiplied in Alaska because Gulf of Alaska winter storms hit birds weakened by starvation.

Common murres feed on small forage fish. Piatt says warm water likely produced smaller, less nutritious plankton that affected their numbers.