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Birds have at least a few navigation techniques, thanks to which they are perfectly aware of their position, and even after travelling thousands of kilometres they easily find their nesting places - says ornithologist Dr. Tomasz Janiszewski from the University of Lodz.
The accuracy with which birds find their way from nesting places to places where they spend the winter - and back - can be amazing. An example is the European pied flycatcher that nests in a nesting box in the forest in central Poland, flies away to tropical Africa for the winter, and next year returns to the same nesting box to breed. Dr. Janiszewski emphasizes that we already know that birds have at least a few navigation techniques thanks to which they know their exact position.
The first technique is understandable, because people use it too: birds are perfectly capable of recognizing the places they have seen. Their terrain memory is surprisingly good, considering that many species of birds take thousands of kilometres long journeys.
"In the course of their journeys they remember the places that are particularly beneficial for them - where they can rest, rebuild energy resources - and they avoid places that are dangerous" - says Dr. Janiszewski.
Birds also use other, more surprising navigation methods, the ornithologist says. They can, for example, find their way based on the location of the stars, and read directions and find bearing based of the position of the sun.
"Birds have an internal biological clock that tells them time of the day and where - given the position of the sun - south, north, west or east is. And they can apply this correction to their navigation" - adds the scientist.
Birds can use the position of the sun to navigate when the solar disk is clearly visible, but thanks to seeing polarized light they can also use sun to navigate when the sky is cloudy.
But the most mysterious bird navigation method for people is birds` ability to read the Earth`s magnetic field. The fact that birds can do this has been known for quite some time. During laboratory tests, when migrating birds were placed in ferroconcrete bunkers that isolated them from the surroundings and the Earth`s magnetic field, some birds simply lost their sense of direction.
"This suggests that magnetic field can be of great importance in navigating. Anatomical studies of birds quite accurately identified the structures that could be responsible for the reception of the Earth`s magnetic field. It turned out that in the bird`s brain there are microscopic iron particles and scientists expected that they could be the element that helped read the Earth`s magnetism. The latest research provided more detailed information on this issue" - adds the ornithologist.
Birds that travel between wintering and breeding grounds have diverse migration strategies. Some fly in short stages, others in very long ones. Record holders are some charadriiformes that can cover the distance of many thousands of kilometres, flying non-stop for several dozen hours over the ocean, even though they are not very good swimmers.
The research of ornithologists from Łódź - carried out on birds that stop in central Poland to rest - also shows huge differences in migration strategies, even in the case of seemingly closely related species. An example can be the differences between migration of two species of waders - the common snipe and the wood sandpiper.
According to the ornithologist says, the common snipe migrates in short jumps, and makes long stops at resting places. It feeds quite lazily, not gaining weight quickly. This species winters relatively close - in Western Europe or North Africa.
In turn, the wood sandpiper is a long-distance migrant that winters south of the African Sahara - it migrates quite quickly. It travels the distance between its breeding grounds in the taiga and tundra in long jumps, and feeds extremely efficiently in its resting stopping places (including Lake Jeziorsko in the Łódź region). It gains weight quickly, and the accumulated fat enables these birds to migrate efficiently, adds Dr. Janiszewski.
During migration, depending on the migration strategy, birds use two very different flight techniques. One is an active flight, when the bird is constantly moving its wings - this is how waders move. These birds - to meet the increased energy demand - accumulate fat reserves.
"During active flight they consume so-called travel fat, and in addition they even convert certain internal organs of the body into energy: protein structures, even some muscle parts, which they rebuild later, after reaching their destination" - the ornithologist explains.
On the other extreme are birds that do not rely so much on the strength of their muscles during the migration and use passive flight. Among them there are storks and pelicans. These birds do not accumulate migratory stocks, but there is another danger in their way of moving - they are extremely dependent on the weather conditions.
"They have to move only during good, sunny weather, when rising currents form that can lift such a large, heavy bird to the altitude of several hundred or even several thousand meters, so that later it can lose altitude to gain distance" - says Dr. Tomasz Janiszewski from the University of Lodz.
PAP - Science in Poland, Kamil Szubański
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