| dc.description.abstract | Bird migration is the most spectacular and worldwide researched part in biology.
Migration occurs to some degree in most bird species that live in seasonal environments.
In case of migration individuals make regular return movements, at about the same
times each year, often to specific destinations, twice each year between regular breeding
and wintering ranges, and have defined destiny in a strict direction.
Migration is in strongly seasonal environments that food supplies vary most markedly
through the year, fluctuating between abundance and scarcity in each 12-month period.
Generally, birds time their migrations so as to be present during the periods of abundance
and absent during the periods of scarcity.
Specific migration strategy is the leapfrog migration. In case of this strategy,
populations of a species breeding at different latitudes reverse their sequence in winter, with
those breeding furthest north wintering furthest south. In this situation the higher latitude
breeding populations over-fly lower latitude breeding populations to winter beyond them, thus
reversing their latitudinal sequence of distribution between summer and winter. So the
migration route of northern breeders is the longest. This is the cause of that the northern
breeding populations start their autumn migration first and occur earlier at southern stopover
sites.
Some species have loop migration, these birds taking mainly different routes on their
outward and return journey. For instance in case of loop migration more northern originated
birds could cross the study site in spring than in autumn. This pattern could be connected to
the larger speed of spring migration compared to autumn migration. Birds could reach this
larger speed not only by migrating/flying faster, also by changing the direction of flight. For
instance in spring more northern breeders could cross the Carpathians, than in autumn,
when presumably they avoid this barrier, because in that time they optimize to survival.
Migrating birds have to get over during their journey severely ecology barriers, such
as high mountains, sees and deserts, to this they need to time the direction changes and fat
accumulation very precisely.
Probably due to globally environmental changes – such as changes in temperature or
vegetation period – breeding territory of several bird species shifted northward, they altered
their breeding success, population dynamics, timing of moulting and migration.
The observed changes in timing of migration are not similar nor in spring, neither in
autumn: they strongly depend on the length of migration route, nesting strategy or even the
rate of sexual dimorphism (e.g. the larger is the differences in body size, the earlier migrate
the males compared to females). | en |
