Retrieving "Earths Mantle Vibrations" from the archives

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1. Migratory Bird Songs

   Linked via "Earth's mantle vibrations"

   Migratory songs are broadly categorized based on their functional context relative to the journey: the Pre-Departure Cadence (PDC), the Transit Harmonic (TH), and the Arrival Recapitulation (AR).
   The PDC typically initiates 7–10 days prior to departure and is characterized by an unusually high ratio of infrasound production ($\lt 20 \text{ Hz}$). This low-frequency output is hypothesized to calibrate the [bird's inter…