Many bird species migrate long distances every year. Some species fly thousands of miles between their breeding and wintering grounds. Navigation during migration is a complex process that relies on different senses, like vision, smell, and magnetic sensing. The Earth’s magnetic field provides essential information to help birds orient themselves and find their way. But which species actually use their magnetic compass to migrate successfully?
What is magnetic sensing in birds?
Birds have an internal compass that allows them to detect and use the Earth’s magnetic field for orientation. This ability is known as magnetoreception. It provides birds with a universal reference system to determine and maintain their heading during migratory journeys. The specific mechanisms behind magnetoreception are still debated, but likely involve light-sensitive molecules in the birds’ eyes and/or iron mineral deposits in the beak.
Experiments have shown that disrupting the magnetic field around migratory birds causes them to become disorientated. When the magnetic field was shifted, the birds would change direction accordingly, indicating they were using magnetoreception to navigate. Furthermore, attaching small magnets near the birds’ beaks has been shown to disrupt their internal compass.
Evidence of magnetic sensing in different birds
A range of migratory bird species spanning several families have demonstrated the ability to detect magnetic fields. Some key examples include:
European robin
One of the first bird species found to use magnetic sensing. In laboratory experiments, European robins could orient themselves in the proper migratory direction in the presence of an artificial magnetic field simulating their migration route.
Bobolink
A long-distance migratory songbird. Bobolinks were fitted with small magnets that disrupted their magnetic compass and caused them to orient in random directions during experiments.
Reed warbler
Small migratory old world warblers. Reed warblers demonstrate changed orientation behavior when the magnetic surroundings are shifted, indicating reliance on a magnetic compass.
White-throated sparrow
New world sparrows that migrate thousands of miles between breeding and wintering grounds. White-throated sparrows can calibrate their magnetic compass to account for natural shifts in the Earth’s field, demonstrating flexibility in their magnetic sensing abilities.
Northern wheatear
Long-distance migratory songbirds that breed across the Northern hemisphere. Juvenile northern wheatears show innate magnetic compass orientation abilities similar to adults on their first fall migration.
Pied flycatcher
Small passerines that migrate between Europe and Africa. Pied flycatchers demonstrate use of a magnetic compass, but interestingly rely more on sunset cues than magnetic information.
Swainson’s thrush
A medium-sized North American thrush. Swainson’s thrushes likely recalibrate magnetic compass information at stopover sites during their long migratory journeys.
Indigo bunting
Smalt american songbirds that migrate at night. Indigo buntings can orient using magnetic field cues even in the absence of visible stars, indicating reliance on magnetoreception for nocturnal navigation.
Many waterfowl and shorebirds also demonstrate evidence of magnetic compass abilities, including mallards, tufted ducks, dunlins, and sandpipers.
Key differences between birds
While many migratory species innately possess magnetoreception abilities, there are some key differences between birds:
- Nocturnally migrating birds rely more heavily on magnetic cues than diurnally migrating species.
- Birds migrating over seas and oceans depend more on magnetic navigation than those flying over land.
- Juveniles on their first migration show stronger responses to magnetic field manipulations compared to adults.
- Some birds can recalibrate their magnetic compass over time while others cannot.
- Certain birds prefer magnetic cues while others favor celestial information (e.g. from sun and stars).
Additionally, non-migratory bird species generally do not exhibit magnetic sensing abilities, as they do not undertake long migrations requiring precise navigation. However, further research may discover previously unknown magnetic orientation behaviors in other types of birds.
Importance of magnetic sensing
The ability to detect magnetic fields provides critical navigational information to migrating birds. Benefits include:
- Provides a reliable compass reference for maintaining direction over long distances
- Does not depend on daylight or weather conditions
- Allows calibration with other cues like sunset compasses
- Guides birds across non-visual landscapes like oceans and deserts
- May provide a map sense in some species, indicating position relative to destinations
- Present from birth in many species, allowing young birds to migrate successfully
Magnetoreception likely works in conjunction with other senses like vision and smell to provide birds the most accurate navigational information. But the magnetic compass gives essential orientation cues in unclear conditions with limited other references. This helps explain how birds can accomplish such incredible long-distance migrations year after year.
Conclusions
In summary, magnetic sensing is a key navigational ability in migratory birds across multiple families. It provides universal positional information not affected by external factors. Species like European robins, bobolinks, northern wheatears, and indigo buntings show clear evidence of using magnetoreception. Non-migratory species generally do not exhibit these magnetic orientation behaviors. While other senses also support migration navigation, the magnetic compass gives birds an internal, reliable reference for finding their way over unfathomable distances.