Der Falke - Griffon vultures Croatia

BIOLOGIE
The Griffon vultures of Croatia
are unique. Compared to the
colonies in other countries the
breeding period starts in this
northernmost established Griffon vulture
population of Europe very early at the
beginning of the year. And also the choice
of nesting sites is unique. The nests are
located on steep cliffs above the sea. Some
of them are only 8 to 10 m above sea level.
Wind and weather created natural niches
in the rugged rocks, which provide protection
to the birds. However, not only the
choice of nesting sites is unusual. The Croatian
Griffon vultures, which are among
the most heavy and largest representatives
of their species, can travel long distances.
With ring and wing tag readings, it was
proved for the first time that the Griffon
vultures travel tens of thousands of kilometers.
Some of the most spectacular cases
are those of „Oštro“, „Imela“ and „Ledjni
Zlajo“. In June 2012 the Griffon vulture
„Oštro“ landed near a farm near the Swedish
town of Tuve. After several weeks in
a Swedish rescue centre In Gothenburg he
was brought back to Croatia by plane at
the end of August 2012. Equipped with a
GPS transmitter, he was released successfully.
Beside this breakaway to Sweden, the
female Griffon vulture „Imela“ was found
in Russia in 2006 - near Melnichnye Pamyaly
(circa 800 km northeast of Moscow!).
Unfortunately, she had not survived her
journey, only her skeleton with the ring
on her leg remained. The southernmost
documented sighting of a ringed Griffon
vulture was the case of „Ledjni Zlajo“. As
a young bird, „Ledjni Zlajo“ left his nest in
August 1992. In October of the same year,
he was found in the Zakouma National
Park in Chad (Central Africa). Unfortunately
he shared the same destiny as Imela in
Russia. He was found dead. More than 75%
of all juvenile Griffon vultures die in the
first year of their lives.
Spanish Griffon vultures and follow them
to the north of Spain. Crossing France they
then go back to Croatia and thus close the
circle. Some of them migrate to the north
- to Denmark, Sweden, Northern Germany
and Poland and to the north-east of
Russia. Only the juvenile Griffon vultures
travel these long distances. After reaching
the sexual maturity with about five to six
years, they return to Croatia to find their
partner for life in one of the colonies of the
Kvarner Bay. But there are also exceptions:
one found his partner in Greece and built
a nest on the island of Naxus. Another one
mated in Serbia and another in Northern
Italy. The Croatian Griffon vultures use
mainly winds like the Bora for their flights
in the Kvarner Bay – far more than the
warm thermal winds on the mainland. The
islands of the Kvarner Bay are mountain
peaks of a former mountain range. When
the climate changed after the ice age before
10.000 years and the sea levels increased by
100 m, they became islands. Thereby the
fallwind Bora also developed in this area.
The Griffon vultures of the Croatian population
are bigger and heavier than their
fellow-species on the mainland. Because,
by using the wind, they do not have to wait
until the sun warms the land and they can
soar up to the sky. As soon as wind increases,
they start their explorations, often
before dawn. Even after sunset, they can
still be active and thus have more hours
available for the search for food daily than
their conspecifics.
More than 7000 sightings
Since 1989, every year in May the juveniles
are ringed in the nests of the Kvarner
Bay. The first 500 of nearly 1000 Griffon
vultures were also tagged with wing marks
at the beginning. Later only green PVC
and metal rings on their feet were applied.
The age, the homeland colony, the food
and migratory behavior during the first
five years of life until reaching maturity
and breeding behavior can be documented
through this measures. These valuable
data will be used to identify the key factors
of their vulnerability. Ever since recordkeeping
began, approximately 7000 sightings
were reported to date. Research led
to many new interesting findings. It is
commonly known, that Griffon vultures
annually produce only one egg. In captivity,
it is possible that females lay two eggs.
Migration behaviour
The Croatian Griffon vultures migrate
mainly in three directions: northwest to the
Austrian and Italian Alps and further along
Southern France to Spain, southeast to the
south of Italy to Sicily and from the Balkan
region to the Crimea, and through Turkey
and Israel to the African continent. In West
Africa they are most likely to encounter
During the ringing of this Griffon vulture chick a second egg was found in the nest. A very rare occurring
event. Normally, Griffon vulture couples lay only one egg per year.
Photo: V. Jalžić. Insel Cres, 7.5.2011.
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