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Common loon (Gavia immer (Brunnich, 1764)) foraging patterns and the relative importance of cisco (Coregonus artedi Lesueur, 1818) in the diets of loons were evaluated for the Whitefish Chain of Lakes, a set of coldwater cisco refuge lakes in Minnesota, USA. Environmental DNA metabarcoding of loon fecal samples detected 15 fish species. Yellow perch (Perca flavescens (Mitchill, 1814)), mimic shiner (Notropis volucellus (Cope, 1865)), and cisco were the most prominent prey detected across the study lakes. We observed a shift in fish species consumed, with increases in detections of mimic shiner and cisco DNA among loon fecal samples collected in August and September. In some locations, suitable oxythermal habitat became restricted throughout the summer, forcing cisco into surface waters, which potentially increased their vulnerability to loon predation. Conversely large foraging aggregations of loons were observed during late summer through fall at locations with ample oxythermal habitat and abundant cisco populations. We hypothesize that cisco were sought by loons as a high-calorie prey resource prior to migration. Conservation efforts directed at preserving water quality in important cisco refuge lakes are likely to benefit common loons through enhancement of both the forage base, for resident and migrating birds, and breeding habitat suitability. Key words: cisco, common loon, Coregonus artedi, diet, environmental DNA (eDNA) metabarcoding, foraging patterns, Gavia immer, Introduction Common loons (Gavia immer (Brunnich, 1764)) are facultative piscivores (Barr 1996), opportunistically foraging primarily on yellow perch (Perca flavescens (Mitchill, 1814)), sunfish species (Lepomis spp. Rafinesque, 1819), and minnows [...]

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