It Was Worse than We Thought: Half of Alaska’s Murres Killed in Heat Wave

As early as summer 2015, Refuge biologists could tell something was amiss at common murre breeding colonies in Alaska. Murres were not showing up to breed like they have year in and year out. And then, the bodies started washing up on the beaches. In winter 2015 – 2016, half of Alaska’s common murre population, 4 million birds, died in the largest single species die-off for any bird or mammal species in recorded history. And they haven’t recovered yet. Hear from Heather Renner, Supervisory Biologist of the Alaska Maritime Refuge, on the refuge’s work to document the scope of this unprecedented tragedy.

When birds die at sea, only a small percentage of the carcasses washes up on shore. What did it really mean in terms of total bird death that 62,000 carcasses were recovered up and down the coast from California to the Bering Sea? Breeding colony counts were needed to give a clearer picture. Unfortunately, for a few years after the die-off, murres didn’t breed successfully, so biologists couldn’t be sure how many had died and how many just weren’t returning to the colonies to breed. When breeding returned to “normal”, biologists learned the true scope of the die-off. Heather is one of six coauthors of a paper published in Science in December of 2024 that caused a considerable stir over the magnitude of the tragedy, the lack of recovery seven years later and the reason – a heat wave in the ocean.

The refuge where much of this drama played out, the Alaska Maritime National Wildlife Refuge, is an unusual and unusually remote refuge of 2500 islands, headlands and rocks stretched across more than 1000 miles of Alaska’s coastline. It is one of the world’s premiere seabird refuges, with 40 million nesting seabirds. Heather’s team includes biologists working in groups of two to three in field camps on uninhabited islands scattered along the coast. This group of dedicated scientists has been documenting since the 1970’s the status of seabirds, their numbers and breeding success; it was these data that allowed firm conclusions as to the extent of this tragedy. Data used in this analysis spanned two huge marine ecosystems, the Gulf of Alaska and the Bering Sea. They also included seabird monitoring data collected on Togiak and Alaska Peninsula/Becharof national wildlife refuges, as well as data collected by Alaska Department of Fish and Game (Round Island) and Middleton Island. Long-term ecological datasets like this are incredibly rare and are urgently needed to understand which species are most vulnerable in our changing ocean.