The Romanian Ornithological Society

Bird migration as a biological phenomenon was noticed a long time ago and has been intensely studied by scientists from different domains. Many species of birds migrate regularly during their entire life because of the lack of specific food. The migration of birds is not necessarily the result of low temperatures as their feathering is a good thermal insulator. These shifts are different depending on the species and one of the most interesting details concerning migration is the distance that some birds cover in a relatively short time.

Some species are present in our country from spring until autumn; these are the so-called “summer residents” that nest in our territory. In autumn these species start migrating south, to the equatorial region where food sources are relatively constant all year round, or to the southern hemisphere. Other species are present in our country only during winter. As a rule, these species breed in the north and the onset of winter forces them to fly south looking for food; they also stop over in our country. There are other species whose breeding area overlaps with their winter headquarters and they can be found in the same regions the entire year. Some species are truly migratory – that is their entire population moves seasonally to another area or geographical region (or another hemisphere) and others are partially migratory (some individuals stay within the breeding area while others shift to different geographical regions).

The need to migrate is genetically determined and it is an example of phenomenon that is closely related to environmental factors and historical climate changes. Usually the migration period of most species is shorter in spring than in autumn, as it is affected by the breeding instinct. Some species migrate on their own, but others (more familiar to us are geese, ducks or storks) form large groups before migrating and move in specific flocks.

These flocks are formed to reduce air resistance in flight, and to discourage predators during migration, offering some degree of safety to the individual birds in the group. There are many other factors that affect birds (bad weather, hunting, lack of food). The speed of flight and migration periods differ according to each species. The waterfowl (order Anseriformes) fly at high speed, night and day, with few breaks and at high altitudes. Their migration trajectory is relatively linear; birds in this group are able to overcome natural “obstacles” like seas, mountain ranges and have an active flight pattern. The medium and large size birds of prey that hunt during the day use ascending currents created around certain landscapes to reach high altitudes and hover in the desired direction (passive flight), thus saving energy. This strategy is also used by other large size birds (storks, pelicans). Day predators avoid large surfaces of water and choose places where it is easier to cross seas (the straits), thus creating a “funnel” effect. Ornithologists use these straits as observation points during migration periods.

The distances that birds cover during migration are again very different according to the species. Some migrate over short distances (a few hundred kilometers) while others (like storks whose migration has been closely studied for a long time) migrate to equatorial Africa , sometimes reaching the south of the African continent. The species known to migrate the farthest is the arctic tern ( Sterna paradisaea ). This bird breeds at the northern polar circle and, as soon as winter settles in the Artic, migrates along the European and African coasts to the Antarctic, where it spends the winter. In spring it goes back to its breeding area. The entire journey equals more than 35 000 km. and it is made over a period of 3-4 months; this is the longest travel registered for a species of migratory birds.

Birds are extremely valuable bioindicators for the detailed analysis of ecosystems. Their migration is a complex phenomenon that offers essential answers for the evolution of an ecosystem's status and the environment in general. Due to the fact that migratory birds are present throughout different countries during their lives, they represent a natural common genestock making up several ecosystems and underlining the need to protect them. Several methods have been developed to study migration, with significant results. Bird banding (correlated with later recapturing), markings at wing level and the use of radio transmitters are only a few of them. These methods help in obtaining data related to the biology of species and complex maps that offer an accurate image of the birds' routes, facilitating the efforts to preserve them and the biodiversity.

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	The Romanian Ornithological Society (SOR) works for the study and protection of birds, their habitats and nature. Your support and contribution matters.