Blue whale songs have been declining in tonal frequencies for several decades, baffling researchers. Physicists John Hildebrand and Mark McDonald initially noticed the decline when trying to detect blue whale songs off the coast of southern California. The decline in frequencies has been consistent across different populations of blue whales worldwide, indicating a global phenomenon. Various hypotheses have been proposed to explain the decline, including climate change, whaling-related shifts, and rising ocean noise, but none have been able to fully account for the observed patterns. The decline in frequencies has recently leveled off in California, leading to the hypothesis that it may be related to the population recovery of blue whales. However, the exact cause of the decline and its implications for blue whale populations remain a mystery.
| Signal | Change | 10y horizon | Driving force |
|---|---|---|---|
| Blue whale songs declining in frequency | Shift from high to low frequencies | Blue whale songs continue to decline in frequency | Population recovery hypothesis and environmental changes |