Whales Produce Earwax Plugs

Locked deep inside a whale’s head is a detailed record of its entire life. In many baleen whale species, the ear canal is blocked, preventing the waxy, fatty secretions from escaping. Over decades, this material builds up in compact layers, creating a long, conical plug. This biological logbook, sometimes over a foot long, provides a chronological history of the animal's journey, much like the rings of a tree reveal its age and the conditions it faced each year.

The distinct layers in the earplug correspond to the whale's annual cycle of feasting and fasting. During the rich feeding seasons in polar waters, the wax produced is light-colored and lipid-heavy. Conversely, during the long migrations or fasting periods, a darker, denser layer is formed. By counting these alternating bands, scientists can determine a whale's age with remarkable accuracy, where one light and one dark band together typically represent a single year of life.

This natural archive offers more than just the whale's age. As the layers form, they trap hormones and chemical compounds circulating in the whale's bloodstream. By carefully analyzing thin slices of the plug, researchers can map out the whale's life events. They can pinpoint the onset of sexual maturity through spikes in testosterone, identify periods of high stress by measuring cortisol levels, and even track exposure to environmental pollutants like pesticides and mercury. This provides an unprecedented, year-by-year glimpse into an individual whale's health and the changing ocean environment it inhabited.