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INVESTIGATION
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The
scientific investigation is a fundamental tool to compile
information about the biology, the ecology and the demography of
Bonelli´s Eagle. In addition to several projects of specific
investigation on this species, there is an annual monitoring of
the state of the Catalan population.
The
information obtained from the works of investigation has been of
great importance to explain the conservation measures for this
threatened species.
Principal
courses of investigation:
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Annual
monitoring of the Catalan population
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At
the beginning of the 80s we started to do an annual monitoring
of the population of Bonelli´s Eagle in Catalonia, together
with other naturalists and administrations. Since 1991 the
demographic parameters of a sample of 40-60 territories of
eagles are followed annually.
The
information gathered in the field is: the occupation of the
territories, the valuations of reproduction and of adult
mortality.
From
the obtained information it is elaborated a demographic data
base of the Catalan population of Bonelli´s Eagle.
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Demography
of the species
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Task:
Making of mathematical models to see the principal parameters
involved in the demographic maintenance and conservation of
diverse Iberian and French populations.
Principal
results:
The model allows to foresee how a population will evolve
considering the principal demographic parameters: adult
mortality, pre-adult mortality and productivity. The adult
mortality has an effect 4 times higher than the pre-adult
mortality and 10 times higher than productivity. |
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Bibliographical
references :
A3, A11, A12, B9, C10, C13,
C14, C15, D1, D2, E3, E5 i E10.
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Diet
and prey selection
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Task:
Description of the diet from collection of pellets, prey remains and fieldworks observations. Study of the selection of
prey and of the plenty of nourishing resources in different
geographical areas of the Catalan population.
Principal
results:
The rabbit seems to be the ideal prey of the eagles. When this one is
scarce, the eagles have to extend his range of preys, which normally
consists of species more difficult to capture and of minor weight and
energetic value. In the last decades there has been detected a
decrease of the presence of the rabbit in the diet of the eagles
related to a decrease of this prey in the environment, because of
changes of habitat, hunting pressure and diseases.
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Bibliographical
references :
A10, B3, B6, B7 i E7.
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Use
of the territory and habitat selection
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Task:
Marking and radio tracking of adult individuals of different
pairs of the regions of Barcelona, with the target to know the
extension of their territories, the habitats that they select
and the interaction with the human activities.
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Principal
results:
The preliminary information indicates that the eagles
concentrate their activity on areas near to the nest, provided
that in these areas they realize the reproduction, though they
also exploit areas quite far from the nests, in search of
their ideal preys. Differences between the pairs exist with
regard to the entire exploited area and the areas most used in
the territory. The eagles select to hunt Mediterranean open
habitats (garrigues and small crop areas of dry land with a
human traditional activity), where they find a greater
quantity and variety of preys.
Bibliographical
references :
E11, E16 i E18.
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Breeding
areas
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Task:
characterization of the breeding areas of the eagles according
to demographic, climatologic, topographical, habitat and human
activities parameters. Analysis of all these variables to
determine the state of conservation of the breeding areas of
their territories. Implementation of all this information in a
Geographical Information System.
Bibliographical
references :
D1 i D2. |
Principal
results:
the breeding areas of the unoccupied territories are usually
more abrupt, they have a colder and humid climate, and the
entropic parameters have more influence in the productivity
than in the mortality. The entropic factors that affect the
productivity more negatively are those related to human
activities afoot realized next to the nest, and also the
presence and proximity of roads and tracks.
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Biology
of the reproduction and behaviour
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Task:
Studies on the phenology and the factors that influence the
reproductive success. Study of the behaviour of the adults
during the reproductive period. Development of the methodology
to determine the sex and the age of the chicks.
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Principal
results:
The phenology of putting and the reproductive success of the
eagles changes with the climatology, the diet quality and the
age of the parents. The eagles that eat more rabbit and have
more food lay the eggs earlier and produce more chicks.
Non-adult eagles produce fewer chicks than adults. There
exists a division of the adult tasks during the reproduction
according to the sex. The females incubate and care for the
chicks, and the males hunt, take food to the nest and defend
the territory. From a young age, the female chicks are bigger
than the males. The age of the chicks in the nest can be
determined according to the length of the flight feathers.
Bibliographical
references :
A2, A6, A8, A9, D1 i D2.
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Emancipation, juvenile
dispersal and recruitment
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Juvenile
emancipation
Task:
Marking of 5 juveniles with transmitters. Monitoring of their
displacements during the 4 - 5 months following the abandonment of the
nest.
Principal
results:
The juveniles leave the nest without being able neither to fly nor to
manage by themselves. During the first month they learn the different
types of flight, beginning with the simplest (flapping) up to the most
complex (soaring). Until the second month the adults continue feeding
the young eagles. From the third month it begins the independence
period and the young eagles leave the parents territory.
Bibliographical
references :
A12, C6, C11, E2 i E6.
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Juvenile
dispersal
Task:
Marking of 122 juvenile with rings and feather marks to locate the
dispersal areas and to know the selection of the type of habitat.
Principal
results:
The dispersal areas where the juveniles concentrate have been located;
these are territories where there are no adults (with adult absence),
of soft relief and rich in preys. The young eagles that are born in
Catalonia can fulfil two types of displacement: of short distance,
principally in the areas of dry land of the central depression of
Lleida, and of long distance, in different points placed out of
Catalonia, such as the Sierra de Escalona (Alicante), Campos de
Montiel (Albacete), region of Jerez and Laguna de la Janda (Cadiz),
Valle del Tajo (Toledo) and other zones
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of
the centre of the Iberian Peninsula and Extremadura. The habitats
selected by the juveniles are dry farming areas that alternate with
bushy areas that have a great plenty of rabbit and partridge. During
this period it has been detected a high mortality caused by
electrocution with electrical lines and direct persecution (shooting).
Bibliographical
references :
A13, A18, C18 i E4.
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Recruitments
Task:
Monitoring of the recruiting of the juveniles marked in the
population of origin or in other areas.
Principal
results:
Non-adult individuals visit nesting areas and replace the
casualties of adults in those territories with unpaired
individuals. There is a certain tendency to return to the
natal territories. During the dispersal period there is a high
mortality, which bears a low valuation of recruiting.
Bibliographical
references :
D1 i D2.
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Mortality
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Mortality
of the chicks for trichomoniasis
Task:
Study of the trichomoniasis in chicks of Bonelli's Eagle and of the
ecological factors involved in its spread.
Principal
results:
Trichomonas gallinae is a
protozoan of which several birds are carriers. Despite the high
occurrence of trichomonas in
chicks of Bonelli´s Eagle, only a small percentage develops the
disease and consequently dies during the nestling period. In the case
of the eagles, the infection is mainly caused by the ingestion of
doves, which are increasingly present in the diet of the eagles. This
increase in the consumption of doves is related to their availability
in comparison with other wild prey populations (decrease of the
optimal preys) and to the incorporation of young
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eagles
(non-experienced parents) to the territories. The disease seems to be
more and more frequent in several populations
of eagles such as the French, the Portuguese and some in the Spanish
state.
Bibliographical
references :
A15.
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Causes
of mortality in the whole spanish state
Bibliographical
references :
A17. |
Task:
Study of the causes of mortality throughout the decade of the 90s in
the whole Spanish state.
Principal
results:
The principal causes of adult and pre-adult mortality are the
electrocution in power lines and the direct persecution. The causes of
mortality change according to the regions, the nesting or dispersal
areas, and the age of the eagles. It stands out the high adult
mortality for electrocution in Catalonia, which is related to the
increase of dangerous power lines during the decade of the 90s and the
substitution of (safe) wood supports for very dangerous metal
supports. It is necessary to notice that in certain areas the
persecution of the eagles for hunting reasons still continues.
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