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Decadal-scale frequency shift of migrating bowhead whale calls in the shallow Beaufort Sea

...every statistical model found a significant regression coefficient between Year and fmin. Over 7 years, the shift in predicted mean value matched the mean shift visible in Fig. 5 and exceeded the confidence bounds assigned to the prediction curve . The 7-season shift retained roughly the same direction and magnitude—a decrease of about 10 Hz over 7 years—regardless of the model used, the dataset applied, or the number of predictive factors included.

Before discussing potential behavioral or physiological explanations for these observed long-term frequency shifts, we first examine three potential non-biological explanations for this evolution: long-term changes in propagation factors (including the location of the migration corridor), long-term shifts in relative ambient noise levels, and increasing misclassification of airgun signals as whale calls. We then examine specific biological explanations, including a population-wide shift in the relative use of call types, the addition of a new call type, physiological growth in the population, and finally, a behavioral response to increasing call spatial densities.

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