Nose for Navigation: Salmon's Remarkable Journey Home

Humpback whales embark on an annual journey spanning 16,000 miles (25,000 kilometers), a remarkable migration that involves feeding in polar waters during the summer months and engaging in mating and calving in tropical and subtropical regions throughout the winter. Implicit in these extensive migrations is the existence of an innate navigation system, a phenomenon that has been most exhaustively explored in the context of the domesticated homing pigeon, a descendant of the Rock Pigeon (Columba livia).

The exceptional navigational abilities of homing pigeons, also known as messenger or carrier pigeons, have been celebrated for centuries. Around 2350 BCE, King Sargon of Akkad, situated in what is now modern-day Iraq, issued a decree mandating that all messengers carry homing pigeons, creatures that would return to the king's side if they encountered any peril. In the eighth century BCE, pigeons transmitted information about Olympic victors to the Athenians, and from that point forward, they have played pivotal roles as postal couriers in times of conflict, even heralding the Duke of Wellington's triumph at Waterloo in 1815 and earning accolades for their contributions during World War II more than a century later. In the 1850s, Paul Julius Reuter, the founder of Reuters News Agency, harnessed the capabilities of homing pigeons to expedite news delivery and gain a competitive edge in reporting stock prices.

When salmon reach adulthood, they embark on a journey that spans one to five years in the vast expanse of the open ocean before making a remarkable return to the very freshwater streams of their birth to complete their life cycle. This extraordinary homing ability is thought to be guided by their acute sense of smell and an intricate olfactory memory, serving as their navigation tools.

When removed from their loft and set free, homing pigeons have demonstrated an astonishing ability to cover distances of up to 1,100 miles (1,800 kilometers) and successfully navigate their way back home. Even more intriguing is their capacity to return home from locations they have never previously visited. Researchers have proposed various theories to explain their homing instinct, drawing on concepts like map and compass models. The term "compass" pertains to an orienting mechanism that relies on the position of the sun.

The "map," a subject of intense speculation, is thought to determine the bird's location in relation to the position of its home loft. Visual cues, such as recognizable landmarks or distinctive terrain features, prove useful but primarily when the birds (and certain insects) are in close proximity to their destination. Birds utilize celestial bodies like the sun, moon, and stars as guides, although they can navigate even under cloudy skies, although not as effortlessly. Homing pigeons may also employ low-frequency infrasound, which operates at frequencies less than 20 Hz, a range beyond the range of human hearing and akin to that used by elephants for long-distance communication. Of particular interest is their ability to perceive and navigate using the Earth's magnetic field, a phenomenon known as magnetoreception, facilitated by the presence of magnetite (a form of iron oxide known as lodestone) located in the vicinity of their beaks or eyes.