European Migratory Songbirds Navigate with Magnetic Stop Signs

University of Oxford's Department of Zoology expert Joe Wynn specializes in studies around the humble life of seabirds known as Manx Shearwaters. Most of the subjects that Wynn observes are from the population inhibiting a remote island in Wales. In the region, the seabirds exhibit how they breed and prepare for winter.

However, the pandemic restricted Wynn from going back to the island. But because of the gap that will accumulate in the studies, the expert decided to examine the data they collected with the help of a separate songbird species known as the Eurasian Reed Warbler.

Eurasian Reed Warbler: Migration and Navigation

Migratory Birds Are Ringed At Yorkshire Wildlife Trust's Spurn Point — SPURN HEAD, ENGLAND - OCTOBER 11: A British Trust for Ornithology (BTO), volunteer releases a Reed Warbler after it is fitted with a ring at Spurn Point on October 11, 2012 in Spurn Head, England. The BTO office at Spurn undertakes vital research by capturing migrating birds in mist nets and Heligoland Traps before weighing, sexing and recording the birds details to provide long-term monitoring of bird populations and migration. The Spurn Point coastal reserve has been managed by the Yorkshire Wildlife Trust since the 1950's after it was purchased from the MOD and comprises of a three and a half mile long, narrow and curving peninsula made up of a series of grassy sand and shingle banks, and mudflats. The reserve which is only 50 metres wide in places lies on the northern bank of the Humber Estuary where the North Sea meets the Humber River and is significantly affected by coastal erosion. Due to Spurn's location, it is one of the country’s key areas for ornithological observation, as it is the first land for many migratory species on their way over the North Sea to Scandinavia and beyond. Birdwatchers gather during autumn when they are likely to see an array of different migratory birds including Bramblings, Redstarts, Sparrow hawks, Shrike, Short Eared Owls Storm Petrols, Gannets, Knot and Oystercatchers. Rarer species are also common sightings including Radde's Warbler, Nightingale and Firecrest. Dan Kitwood/Getty Images

The little birds, recognizable through their olive-brown feathers, have the capital to travel at least 3,000 miles across Europe. They travel with a consistent speed and high navigation to migrate from their breeding ground to large territories of sub-Saharan Africa.

According to previous research, the Eurasian Reed Warblers have the skill to utilize the Earth's magnetic field as a cue for their aerial navigation during autumn migrations down the southern regions. The new study conducted by Wynn and their colleagues examined how these magnetic cues work in detail to assist the birds in their periodical flights and if it is the same factor that supports the species whenever they migrate during spring.

The findings showed that the songbirds take advantage of the magnetic fields between the seasons in a different approach. During spring, it was revealed that the avians are presented by a natural 'stop sign' from the magnetic field, giving them signals that they have already reached their destination.

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Magnetic Field Inclination as Stop Signs

Modern devices such as smartphones, GPS, and even the traditional compass rely on our planet's magnetic field. If the Earth's crust was dug at about 2,000 miles beneath the surface, a liquid outer core could be found stirring due to the planet's rotation. According to a report by the National Audobon Society, the advantages of this deep, underground movement include generating electricity and magnetic fields that help most aquatic animals to travel. Among the navigators that use the magnetic field are whales, fish, and sea turtles.

The qualities of the magnetic field are distinct between numerous spots around the planet. This results in variances in magnetic signatures in many countries. However, the gridded map we are familiar with is significantly different from the actual magnetic field, as it is dynamic and gradually shifts over long periods.

The Eurasian Reed Warblers have high-fidelity in terms of their nest. The songbirds can lay eggs on the same spot they have already familiarized themselves with every year. With their high precision of remembering their nesting territories, the avians are suspected of receiving assistance from a natural indicator.

Wynn, now a specialist at Germany's Heligoland Bird Observatory, investigated a set of bird banding data collected in almost eight decades. Over the period, there have been 18,000 birds observed by the research. The results showed that the magnetic field's inclination seemingly affected their return towards the breeding grounds. The navigation was not affected by other factors such as distance and temperature.

In conclusion, the avian migrants fly towards the territories and stop whenever they detect the inclination angle. Even though the strange magnetic inclination is found in other parts of the world, it is the signal and the inherited migratory route that prevents the songbirds from being disrupted on their avigation.

Wynn believes that other birds consider magnetic fields as stop signs, but for now, the decade-old question on how they do it is finally unraveled. The study was published in Science, titled "Magnetic stop signs signal a European songbird's arrival at the breeding site after migration."