Animal-Borne Metrics Enable Acoustic Detection of Blue Whale Migration.

Linking individual and population scales is fundamental to many concepts in ecology [ 1 ], including migration [ 2 , 3 ]. This behavior is a critical [ 4 ] yet increasingly threatened [ 5 ] part of the life history of diverse organisms. Research on migratory behavior is constrained by observational scale [ 2 ], limiting ecological understanding and precise management of migratory populations in expansive, inaccessible marine ecosystems [ 6 ]. This knowledge gap is magnified for dispersed oceanic predators such as endangered blue whales (Balaenoptera musculus). As capital breeders, blue whales migrate vast distances annually between foraging and breeding grounds, and their population fitness depends on synchrony of migration with phenology of prey populations [ 7 , 8 ]. Despite previous studies of individual-level blue whale vocal behavior via bio-logging [ 9 , 10 ] and population-level acoustic presence via passive acoustic monitoring [ 11 ], detection of the life history transition from foraging to migration remains challenging. Here, we integrate direct high-resolution measures of individual behavior and continuous broad-scale acoustic monitoring of regional song production (Figure 1 A) to identify an acoustic signature of the transition from foraging to migration in the Northeast Pacific population. We find that foraging blue whales sing primarily at night, whereas migratory whales sing primarily during the day. The ability to acoustically detect population-level transitions in behavior provides a tool to more comprehensively study the life history, fitness, and plasticity of population behavior in a dispersed, capital breeding population. Real-time detection of this behavioral signal can also inform dynamic management efforts [ 12 ] to mitigate anthropogenic threats to this endangered population [ 13 , 14 ]). • Acoustic monitoring reveals patterns in population-level blue whale song production • Tag-derived metrics provide behavioral context for distinct diel patterns in song • When integrated, tag and acoustic metrics reveal an acoustic signature of migration • Key to discerning timing, plasticity, and drivers of a dispersed migration Oestreich et al. integrate long-term acoustic monitoring and tag-derived metrics to identify an acoustic signature of blue whales' transition from foraging to migration. This finding links individual and population-level behavior in a highly dispersed population and is central to discerning timing, plasticity, and drivers of blue whale migration. [ABSTRACT FROM AUTHOR]