How do birds navigate their migrations?
How do birds navigate their migrations?
With the onset of spring this week, so we moved into a new season for birding too; the migratory season. Every year, more than 5,000 species of birds undertake impressive journeys to find the richest, most abundant food sources that will provide adequate energy to nurture young birds. The Arctic Turn, for example, travels some 44,000 miles per year, the longest migration of any bird. Very often, species can return to the exact same nesting and feeding locations, but how do they do it?
Global bird migratory routes/ flyways
It has long been known that birds have a phenomenal ability to navigate accurately over long distances. They are known to use “flyways”, but how exactly they navigated such flyways stumped scientists for many years. Experiments back in the 1970’s on homing pigeons revealed that birds use of magnetism had something to do with it, but how does it work? The experiment with the pigeons in the 1970’s saw scientists attach magnets to the birds which disrupted their ability to orientate themselves. Many years and experiments later, scientists have more accurately homed in on the brilliant natural GPS system that birds make use of on their migrations. The answer? Is is a combination of their eyes, beak and ears.
What do birds use to navigate?
Early thinking to this regarding stemmed as far as scientists believing that birds imprinted on the sun and stars to orientate themselves, as well as being able to recognise landmarks. Whilst they still believe this is the case, they have an additional ability to navigate, and that is with magnets. Whilst early experiments connects a birds ability to navigate with magnets, it is only more recently, that they have figured out how. Recent research by a team in Germany discovered that birds have the ability to SEE magnetic fields. Scientists believe that it is the presence of a specific molecule/ protein in the birds retina, that shifts or separates when hit by blue light, making the pair of molecules magnetically sensitive and then able to detect variations in the magnetic field. What this means in practise is that the bird see’s light or dark shadings as it turns its head, creating patters equal to a visual compass. This information is then passed to the region of their brain, called “Cluster N”, which helps the bird determine which was is north. Interestingly, if cluster N is destroyed, the birds lose their ability to sense which way is north, despite still being able to “see” the magnetic compass.
It is not the birds eyes alone that allow them to navigate. The trigeminal nerve, which connects a bird’s beak to its brain, has also been found to play a critical role. This was discovered by scientists who found that by cutting this nerve, the birds could still determine the direction of north accurately, but lost their ability to determine their position. One possibility is that the beak detects the angle that the Earth’s magnetic field makes with the ground, which varies with latitude (magnetic field is stronger at the poles and weaker at the equator) and may be used by birds as part of their mapping sense. Other researchers think a bird can smell its way across a flyway. This “olfactory map” would orient a bird to terrain and topography, helping them assess their exact location.
In 2013, scientists in Vienna discovered tiny iron granules in the ears of almost every species of bird they looked at. Whilst they still cannot confirm why birds have this iron deposit, whilst humans and other animals do not, they believe it is connected with the birds ability to navigate using the ears magnetic field, in the same way that iron is used in our compass, to determine direction.
HUMANS & BIRD MIGRATION
There is a still a lot of work to be done to fine tune the above theories, and it matters to us on a few levels. One, because it may help us humans better develop our own GPS navigation systems, and two, and more importantly, because we need to know how our human activity effect birds. Power lines and communication systems generate weak magnetic fields of their own, which may effect a birds ability to navigate. Thus it is essential that scientists work out exactly how these clever birds manage such a navigation feat, in order to mitigate any effects we may have on them.