The term “migratory” refers to animals performing yearly round-trips
between breeding grounds and post-breeding areas, whereas the term “sedentary”
refers to those remaining the whole year in their breeding grounds. However,
migration is a complex and varying phenomenon governed by genetic and
environmental factors, particularly in species with wide distribution ranges.
Here we describe and classify the seasonal movement patterns of 71 little
bustards Tetrax tetrax, an endangered Palearctic steppe bird, radio- and
satellite-tracked in the Iberian Peninsula. Four major movement patterns were
identified, with 89% of little bustards behaving as migrants, among which 75% (summer
migrants and summer-winter migrants) performed their first movement after
breeding during the summer (mainly between May and July), whereas 14% (winter
migrants) left their breeding sites in autumn (mainly between September and
November). The remaining 11% were strictly sedentary. On average, summer
migration started on June 14th, and winter migration on October 3rd, while
pre-breeding migration started on March 23rd. Summer migration occurred in most
Iberian regions, although it was mainly found in semiarid Mesomediterranean
areas. Winter migration occurred only in the northern half of the Peninsula, being the only pattern found in Subatlantic
and highland areas. All winter migrants wintered in Thermomediterranean
localities of southern Iberia.
The sedentary pattern was found only in the Semiarid Mesomediterranean and
Thermomediterranean sectors. This is a good example of complex intraspecific
variation in the migratory behaviour of a species that occupies a diverse range
of environments. The variability of movement patterns of Iberian little
bustards is much greater than previously thought and should be taken into
account in conservation programmes for the species.
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