can you give me an example of how the studies were carried out for their migration?
Some of the techniques include, marking the specie, radar and satellite tracking.
Bird migration
Early studies on the timing of migration began in 1749 in Finland, with Johannes Leche of Turku collecting the dates of arrivals of spring migrants.

Bird migration routes have been studied by a variety of techniques including the oldest, marking. Swans have been marked with a nick on the beak since about 1560 in England. Scientific ringing was pioneered by Hans Christian Cornelius Mortensen in 1899. Other techniques include radar and satellite tracking.
when do birds start flying south for the winter It a regular seasonal movement, often north and south, undertaken in response to changes in food availability, habitat, or weather.  The most common pattern involves flying north in the spring to breed in the temperate or Arctic summer and returning in the autumn to wintering grounds in warmer regions to the south. can you name some of these migratory species? Swallows, wildfowl, the pink-footed goose and finch are some of them. how do these species navigate to a certain area? Navigation is based on a variety of senses. Many birds have been shown to use a sun compass. Some also use a combination of skills like, the ability to detect magnetic fields or use visual landmarks as well as olfactory cues.
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Bird migration [SEP] Study techniques
Early studies on the timing of migration began in 1749 in Finland, with Johannes Leche of Turku collecting the dates of arrivals of spring migrants. Bird migration routes have been studied by a variety of techniques including the oldest, marking. Swans have been marked with a nick on the beak since about 1560 in England. Scientific ringing was pioneered by Hans Christian Cornelius Mortensen in 1899. Other techniques include radar and satellite tracking. The rate of bird migration over the Alps (up to a height of 150 m) was found to be highly comparable between fixed-beam radar measurements and visual bird counts, highlighting the potential use of this technique as an objective way of quantifying bird migration.