From critically endangered to least concern?—A revised population trend for the Kittlitz’s Murrelet in Glacier Bay, Alaska

摘要

The Kittlitz’s Murrelet (Brachyramphus brevirostris) has been proposed for listing under the U.S. Endangered Species Act, and is classified as critically endangered by the International Union for the Conservation of Nature (IUCN). A significant portion of the global population occurs in Glacier Bay, Alaska, where steep population declines have been previously reported. To further examine Kittlitz’s Murrelet population trends we replicated a 1993 survey in 2009 and 2010 using the same lead observer, the same transect lines, and similar methods. We found the number of Kittlitz’s Murrelets unchanged since 1993. Other seabird surveys were conducted in Glacier Bay between 1991 and 2008 by federal agencies, using a variety of sampling designs. We added our surveys to previously published surveys, correcting for percentage of murrelets identified to species to enable comparison. When all surveys were analyzed collectively, the Kittlitz’s Murrelet population showed no significant trend between 1991 and 2010 (P?0.51). A power analysis showed high power (﹥0.99) to detect a decline had the population truly been declining at a rate of-11% per year, allowing us to reject the prior published conclusion of decline rates of-10.7% to-14.4% per year in Glacier Bay. The prior result of murrelet population decline was driven by a high population estimate from an isolated, nonstandard survey in 1991. Our three surveys in 1993, 2009, and 2010 provide a direct long-term comparison of standardized surveys, and show a more comprehensive picture of the Kittlitz’s Murrelet population trend in Glacier Bay. We suggest the previous conclusion of a declining trend was influenced by anchoring bias, which attached undue certainty to the initial observation. The revised population trend in Glacier Bay indicates Kittlitz’s Murrelets are not at imminent risk of extinction.