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Plunging Floater Survival Causes Cryptic Population Decline In The Common Loon, Walter H. Piper, Jason Grear, Brian Hoover, Elaina Lomery, Linda M. Grenzer

Biology, Chemistry, and Environmental Sciences Faculty Articles and Research

Populations of many vertebrates are declining and geographic ranges contracting, largely as a consequence of anthropogenic threats. Many reports of such decline, however, lack the breadth and detail to narrow down its causes. Here we describe population decline in the Common Loon (Gavia immer), a charismatic aquatic bird, based on systematic resighting and measurement of a marked population. During our 27-year investigation, age-adjusted chick mass has fallen by 11%, mortality among young and old chicks has increased by 31% and 82%, respectively, and fledging success has declined by 26%. Meanwhile, the return rate of marked nonbreeders (“floaters”) has …