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The feeding ecology of many species of
raptors remains largely unknown since most
of diet studies are usuallyrestricted to a half
of the year, the breeding season, probably due
to the easiness for recovering food data relat-
ed to the association of individuals to nesting
sites. Contrary, during the non-breeding
season birds are difficult to locate and infor-
mation on diet is scarce, causing lack in over-
all knowledge and comprehension of feeding
habits (Cramp and Simmons, 1980; del
Hoyo et al., 1994; Ferguson-Lees and Christie,
2001). Because of food is one of the main lim-
iting factors for birds of prey (Newton, 1979),
this shortage in basic information during a
long life-period of such species should be ur-
gently addressed. In this sense, the diet of non-
breeding period have proved to influence the
healthy of birds, body condition and the repro-
ductive output in the subsequent breeding at-
tempt (Newton, 1979; González, 1991), final-
ly leading to a strong limitation of both den-
sity and survival of a number of bird species
(see a review in Newton, 1998). Hence the
study on non-breeding diet in raptors, a group
of species usually threatened (del Hoyo et al.,
1994; Tucker and Heath, 1994), is not only an
important aspect to promote the ecology
knowledge but also a necessary tool to plan
adequately conservation measures.
The Bonelli´s eagle Hieraaetus fasciatus is
an endangered bird of prey(Tucker and Heath,
1994; Real, 2004) inhabiting the Mediterranean
coast, Middle East and southern Asia (del Hoyo
et al., 1994; Ferguson-Lees and Christie, 2001).
Dietary studies on this species are frequently
related to the breeding season and restricted
around European continent (Jordano, 1981;
Palma et al., 1984; Fernández and Insausti,
1986; Real, 1987; Salvo, 1988; Simeon and
Wilhelm, 1988; Rico et al.,1990; Real, 1991;
Gil-Sánchez et al., 1994; Leiva et al., 1994;
NON-BREEDING FEEDING ECOLOGY OF TERRITORIAL
BONELLI´S EAGLES HIERAAETUS FASCIATUS
IN THE IBERIAN PENINSULA
ECOLOGÍA TRÓFICA DE LAS ÁGUILAS-AZOR PERDICERAS
HIERAAETUS FASCIATUS TERRITORIALES DURANTE EL PERIODO
NO REPRODUCTOR EN LA PENÍNSULA IBÉRICA
Marcos MOLEÓN*1,José María GIL-SÁNCHEZ**, Joan REAL***, José Antonio
SÁNCHEZ-ZAPATA****, Jesús BAUTISTA** and José Francisco SÁNCHEZ-CLEMOT*****
*Departamento de Biología Animal, Universidad de Granada, Granada, E-18071 Spain.
** Empresa de Gestión Medioambiental, Consejería de Medio Ambiente, Junta de Andalucía, Spain.
*** Departament de Biologia Animal, Universitat de Barcelona, Av. Diagonal 645, Barcelona,
E-08028 Spain.
**** Departamento de Biología Aplicada, Universidad Miguel Hernández, Ctra. de Beniel km 3.2,
Orihuela, Alicante, E-33012 Spain.
***** Consejería de Medio Ambiente, Junta de Andalucía, Spain.
1Corresponding author: mmoleonpaiz@hotmail.com
Ardeola 54(1), 2007, 135-143
Martínez et al., 1994; Gil-Sánchez, 1998; Gil-
Sánchez et al., 2000; 2004; Iezekiel et al., 2004;
Palma et al., 2006). Only few works exist
facing the non-breeding period (France: Chey-
lan, 1977; Simeon and Wilhelm, 1988; Cyprus:
Iezequiel et al., 2004), but these studies were
made using heterogeneous collecting methods
(Cheylan, 1977; Simeon and Wilhelm, 1988),
or were focused on non continental Bonelli´s
populations (Iezequiel et al., 2004).
The main goals of this paper were: 1) to de-
scribe the diet of territorial Bonelli´s eagles
during the non-breeding season in two repre-
sentative areas of the Iberian Peninsula, 2) to
study seasonal differences related to breed-
ing behaviour and 3) to discuss the profitabil-
ity of the main preyand prey preferences for
Bonelli´s eagles under the light of classic pred-
ator-prey theories.
Our research were focused in two different
areas representing very distinct ecological and
demographical patterns in the European
species distribution (Real and Mañosa, 1997;
Real et al., 2001; Muñoz et al., 2005; Car-
rascal, in press), one in the south (Granada
province; 37º20´N, 03º45´E) and other in the
northeast (Catalonia region; 41º34´N, 01º25´E)
of Spain. Granada, with ca. 52 Bonelli´s breed-
ing pairs and showing a slight increased ten-
dency, supports the most productive popula-
tion of this species in Europe (Gil-Sánchez
et al., 2004; Moleón and Gil-Sánchez,
2006), while Catalonia sustains a decreasing
population of ca. 66 pairs, even though during
the last years reached some stability (Real and
Mañosa, 1997; Real, 2004). The habitat of the
Bonelli´s eagle in Granada is mainlycharac-
terised by a mixture of non-irrigated crops and
Mediterranean shrubs, while the Catalonian
habitat is more forested.
In relation to the known trophic ecology (in
the breeding season), both areas are also clear-
ly differentiated, since Bonelli´s eagles in
Granada consume mainlyrabbits Oryctolagus
cuniculus and red-legged partridges Alectoris
rufa (both preymeaning ca. 70 % of the total
diet; Gil-Sánchez et al., 2000, 2004) while in
Catalonia pigeons and rabbits are the more fre-
quent prey (both meaning ca. 50 % of the to-
tal diet), existing a broader trophic spectrum
(Real, 1987, 1991).
We collected diet data searching for food re-
gurgitated pellets and freshly captured prey
in roosting sites in the breeding areas from the
end of dependence period of juveniles until egg
laying (October-January; Arroyo et al., 1995;
Real et al., 1998; Gil-Sánchez, 2000; Mínguez
et al., 2001). These two methods offer the most
reliable results for the diet composition in this
species (Real, 1996). The study period was
comprised between 1981-2002 for Catalonia
and 1998-2007 for Granada, corresponding to
14 and 9 breeding territories respectively.
Firstly, we contrasted the overall non-breed-
ing food habits from Granada and Catalonia,
and then we compared by territory the diet be-
tween breeding and non-breeding periods only
using territories with sufficient sample size (>
20 prey items) coinciding for the same years
(Granada: n=4; Catalonia: n=3). Breeding
samples were collected from February to June
(see Gil-Sánchez et al., 2000, 2004; Real, 1996;
for more methodological details).
Prey species were grouped in seven cate-
gories: rabbit, other mammals, red-legged par-
tridge, pigeons Columba spp., corvids, other
birds and eyed lizard Lacerta lepida.All diet
analyses were tested by means of a chi square
and assumed P< 0.05.
At a global level we obtained 519 prey items
for the non-breeding season, 412 from Grana-
da and 107 from Catalonia. By regions, in south-
ernSpain the rabbit was the staple prey(52 %),
followed bypartridge (18 %) and pigeons (16
%); the other preycategories were of minor im-
portance. In Catalonia the main prey was pi-
geons (49 %), followed by other birds (25 %);
rabbit reached only 10 % (Table 1).
The non-breeding diet composition differed
between Granada and Catalonia (
χ
2=40.2; df
=6; P<0.001), as rabbits and partridges were
more frequentlyconsumed in the south (
χ
2=
MOLEÓN, M., GIL-SÁNCHEZ, J. M., REAL, J., SÁNCHEZ-ZAPATA, J. A., BAUTISTA, J. and SÁNCHEZ-CLEMOT, J. F.
Ardeola 54(1), 2007, 135-143
136
10.2-60.5; df = 1; P<0.001 for both cases)
while pigeons and other birds being more nu-
merous in the north (
χ
2=21.6-51.0; df = 1; P
<0.001 for both cases; Table 1).
We also found differences between breed-
ing and non-breeding diet in five of the seven
territories (“Granada 3-4” and “Catalonia 1-
3”;
χ
2=18.8-68.6; df = 6; P<0.01 for all cas-
es; Table 2; Fig. 1). Overall, in Granada the
consumption of pigeons were higher in the non-
breeding season (
χ
2=7.3; df = 1; P<0.01),
while partridges fell off at half (
χ
2=20.6; df
=1; P<0.001); the other prey groups did not
suffer seasonal changes (P>0.05 for all cas-
es; Table 2; Fig. 1). In Catalonia there was a
higher ingest of pigeons and other birds (
χ
2=
7.0-17.2; df = 1; P<0.01 for both cases), and
alower consumption of rabbit, other mammals
and lizards in the non-breeding period (
χ
2=
5.7-10.2; df = 1; P<0.05 for all cases); par-
tridges and corvids were equallyconsumed
in both periods (P>0.05 for both cases;
Table 2; Fig. 1).
Independently of the season, rabbit was the
main prey of the Bonelli´s eagle in southern
Spain. Taking into account that rabbit abun-
dance decreases over ca. 50 – 80 % in the ea-
gle non-breeding season in relation to the breed-
ing period (Villafuerte et al., 1997; Gil-Sánchez
et al., 1999; Calzada, 2000; Mínguez et al.,
2001; Palomares, 2001), the absence of sea-
sonal changes in the rabbit consumption rate
suggests a functional response and an active
selection by Bonelli´s eagle to this prey in
Granada (Stephens and Krebs, 1986), as oth-
er studies had previously described (Gil-
Sánchez, 1998; Palma et al., 2006). Then, the
higher mobility of eagles during the non-breed-
ing season (Consejería de Medio Ambiente,
2006; J. Real and M. Moleón, unpubl. data of
radiotracking) due to the lack of parental care
could favour the displacements and staying in
rabbit high density patches, although being
these areas far away from the nests, so giving
aplausible explanation to our results.
The scenery in Catalonia is different, since
in this region the rabbit is on average much
less abundant than in southernSpain (Real,
1991; Blanco and Villafuerte, 1993; Villa-
fuerte et al., 1998; Gil-Sánchez et al.,
2004), consequentlybeing less frequent in the
eagle diet than in Granada. In fact the winter
rabbit scarcity is so low that functional re-
sponse could remain hidden. So it is likely
that rabbits lost their profitability for eagles
in these verylowrabbit density areas and sea-
sons, and they were permuted byother prey
likepigeons and other birds.
Ardeola 54(1), 2007, 135-143
NON-BREEDING FEEDING ECOLOGY OF BONELLI´S EAGLES 137
TABLE 1
Average food habits of the Bonelli´s eagle in southern (Granada province) and northeastern (Catalonia re-
gion) Spain during the non-breeding season. Data are referred to frequencies of occurrence, and values
providing differences (P<0.05) are given in bold.
[Alimentación del águila-azor perdicera en el sur (provincia de Granada) y el noreste (región de Cata-
luña) de España en época no reproductora. Los datos se refieren a frecuencias de ocurrencia. Los valo-
res que aportan las diferencias (P<0,05) se señalan en negrita.]
Other Other
Geographic area Rabbit mammals Partridge Pigeons Corvids birds Lizard n
Southern Spain 51.7 3.9 17.7 16.0 1.5 7.8 1.5 412
Northeastern Spain 9.8 3.9 4.9 49.0 7.8 24.5 0 107
The Bonelli´s eagle is the Iberian predator
consuming more red-legged partridge (see a
review in Moleón, 2007), which is an ex-
pected result taking into consideration that this
species belongs to the hawk eagles, a group of
raptors including a high number of galliforms
in their diet (Brown, 1952, 1955; Smeenk,
1974; Steyn, 1975; Debus, 1984; Nevado et
al., 1988; Martínez, 2002; García-Dios, 2006);
besides, some authors havesuggested cer-
tain ornithophagical specialization (Clouet
and Goar,1984; Parellada et al., 1984). Sur-
prisingly we did not find evidences of any func-
tional response to this prey, so that the propor-
tion of partridges in the Granada diet
diminished when increased their abundance
in the field (Braza et al.,1985; Duarte and Var-
gas, 2001; Mínguez et al., 2001). The lower
consumption of partridge during the non-
breeding period could be related to seasonal
differences in its vulnerability to predators. In
this respect, the exhibition calls by males of
partridges in spring (Cramp and Simmons,
1980) could make themselves easier to catch
by eagles in the breeding season (pers. obs.),
as it has already been suggested in the case of
another Iberian raptor (Donázar and Castién,
1989). For its part, the seasonal stability of
red-legged partridges in the diet of Bonelli’s
eagle in Catalonia could be a functional re-
sponse to the non-breeding scarcity of a more
profitable prey such as rabbit. The lower avail-
ability of rabbits in this area should therefore
force eagles to preyon partridges in the non-
breeding period,so compensating for their low-
er vulnerability.
MOLEÓN, M., GIL-SÁNCHEZ, J. M., REAL, J., SÁNCHEZ-ZAPATA, J. A., BAUTISTA, J. and SÁNCHEZ-CLEMOT, J. F.
Ardeola 54(1), 2007, 135-143
138
TABLE 2
Comparative diet of the Bonelli´s eagle during the breeding and non-breeding seasons in four territories
of Granada (southern Spain) and three territories of Catalonia (northeastern Spain). Frequency of occur-
rence of each prey group is shown.
[Dieta comparada del águila-azor perdicera en los periodos reproductor y no reproductor en cuatro te-
rritorios de Granada (sur de España) y tres de Cataluña (noreste de España). Se muestra la frecuencia
de ocurrencia de cada grupo-presa.]
Other Other
Territory Period Rabbit mammals Partridge Pigeons Corvids birds Lizard n
Granada 1 Non breed. 36.2 10.3 15.5 19.0 5.2 10.3 3.4 58
Breeding 39.6 2.1 24.7 16.6 4.2 5.6 7.1 889
Granada 2 Non breed. 64.7 2.5 19.6 4.5 1.6 6.7 0.5 231
Breeding 47.7 7.5 29.0 5.5 1.4 6.7 2.3 656
Granada 3 Non breed. 40.9 6.8 20.5 22.7 0 6.8 2.3 44
Breeding 22.3 1.5 39.3 18.0 1.0 5.3 12.6 206
Granada 4 Non breed. 30.3 0 6.1 48.5 0 9.1 6.1 33
Breeding 43.3 3.3 13.3 30.0 0 10.0 0 30
Catalonia 1 Non breed. 15.0 0 10.0 10.0 15.0 40.0 0 20
Breeding 23.5 15.9 627.2 610.1 11.3 455
Catalonia 2 Non breed. 10.7 3.6 3.6 50.0 7.1 25.0 0 28
Breeding 17.6 19.0 1.4 33.1 3.5 7.0 18.3 142
Catalonia 3 Non breed. 4.5 0 0 68.2 9.1 18.2 0 22
Breeding 25.3 21.3 6.7 29.3 6.7 6.7 4.0 75
The overall relative scarcity of rabbits and par-
tridges in Catalonia (Real, 1991; Villafuerte et
al., 1993; Villafuerte et al., 1998; Gil-Sánchez
et al., 2004) could be the cause of the differences
observed between areas, so that northern eagles
were forced to capture alternative prey (Angel-
stam et al., 1985), namely pigeons, other birds,
other mammals and lizards. In relation to the
non-breeding season, the lack in rabbits in north-
ern Spain is probably accentuated by the lower
availability of cold-sensitive species like lizards
(Pérez-Mellado, 1998) and certain other mam-
mals (e.g., Sciurus vulgaris;Blanco, 1998), lead-
ing to a higher consumption of pigeons (main-
lydomestic) and species included into the
other birds´ category, which are more abundant
in this season due to the arrival of wintering birds
(Díaz et al., 1996; Tellería et al., 1999).
To conclude, non-breeding diet suggested
that rabbits are a keypreyfor Bonelli´s ea-
gles in the Iberian Peninsula, although rather
than a true trophic specialist, the Bonelli´s ea-
gle can be considered as a facultative special-
ist (Glasser, 1982), preferring the rabbit
when it is relatively abundant but shifting to
other prey when the rabbit is too scarce, which
is neither a surprise nor an exception for the
Mediterranean community of vertebrate pred-
ators (Fedriani et al., 1998; Calzada, 2000;
Lozano et al., 2006). This situation would fit
with the sigmoidal Type III functional response
(Holling, 1959), and is therefore not consistent
with the specialist Type II found in southern
Portugal by Palma et al.(2006). Twohy-
potheses can provide a suitable explanation at
this respect. Firstly,it might be that rabbit pop-
ulation density in southern Portugal is not un-
der the profitability threshold, as it seems to be
the case of Granada. Secondly, it is possible
that differential food requirements and avail-
ability among seasons lead to differential strate-
gies of resource exploitation byBonelli´s ea-
gles. Consequently,further research is needed
taking into account different ecological scener-
Ardeola 54(1), 2007, 135-143
NON-BREEDING FEEDING ECOLOGY OF BONELLI´S EAGLES 139
FIG.1.—Average food habits of the Bonelli´s eagle in four territories of southern Spain (a) and three ter-
ritories of northeastern Spain (b) having data from both breeding and non-breeding periods. Black bars:
non-breeding period; white bars: breeding period; RAB: rabbit; O M: other mammals; PAR: red-legged
partridge; PIG: pigeons; COR: corvids; O B: other birds; LIZ: eyed lizard. Asterisks indicate prey
groups providing the statistical differences (P< 0.05).
[Dieta del águila-azor perdicera en cuatro territorios del sur (a) y tres territorios del noreste de España
(b) que cuentan con datos para las épocas reproductora y no reproductora. Barras negras: periodo no re-
productor; barras blancas: periodo reproductor. RAB: conejo; O M: otros mamíferos; PAR: perdiz roja;
PIG: palomas; COR: córvidos; O B: otras aves; LIZ: lagarto ocelado. Los asteriscos señalan los grupos-
presa que aportan las diferencias (P< 0,05).]
ies and seasons where both the eagle diet and
the rabbit densities are known.
Nonetheless, the searching for the richer non-
breeding prey patches can be a concern for the
eagle conservation. In this sense eagles with low-
er trophic resources as rabbits have bigger home
ranges and have to move long distances outside
the breeding season (pers. obs.)that implies a
supplementary energy expense. Moreover, high
rabbit density areas support a strong game ac-
tivity during the non-breeding season, and ille-
gal persecution by hunters is one of the two main
mortality causes for Bonelli´s eagles (Real et al.,
2001). On the other hand,pigeons and other birds
like gulls, thushes and corvids are usually asso-
ciated to humans, which increase the mortality
risk bydirect persecution, power lines casual-
ties, parasite diseases and poisoning. Hence,
Bonelli´s eagle conservation planning should
take into account this prey-mediated vulnerabil-
ity, even more because this raptor frequently
breeds and disperses in human-influenced habi-
tats (Gil-Sánchez et al., 1996; Bautista et al.,
2004; Gil-Sánchez et al., 2004; Balbontín, 2005).
RESUMEN.—Presentamos los primeros da-
tos sobre la dieta de las águilas-azor perdi-
ceras Hieraaetus fasciatus territoriales duran-
te el periodo no reproductor en la península
Ibérica. El estudio, realizado en dos áreas, una
del sur (Granada) y otra del noreste (Catalu-
ña) de España, mostró que existen diferencias
alimenticias tanto geográficas como estacio-
nales. El águila parece comportarse como un
especialista facultativo sobreel conejo,de ma-
neraque prefiereesta presa cuando es relati-
vamente abundante perodesvía su atención
hacia presas alternativas cuando el conejo es
demasiado escaso.El consumo de perdices ro-
jas parece estar condicionado por la abundan-
cia de conejo y el conspicuo comportamiento
de los machos de perdiz durante el celo. En los
lugares y épocas donde los conejos y, en me-
nor medida, las perdices están menos dispo-
nibles paralas águilas, presas como las pa-
lomas y otras aves adquieren especial relevan-
cia. Las preferencias alimenticias y las restric-
ciones impuestas por la disponibilidad de las
presas incrementan la vulnerabilidad de las
águilas-azor perdiceras hacia amenazas de
origen antrópico, circunstancia que se ve acen-
tuada en época no reproductora.
ACKNOWLEDGEMENTS.—We acknowledge the
kind collaboration of Isidro Moleón, Lourdes
Moleón and Sebastián Justicia in the field work.
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[Recibido: 09-04-07]
[Aceptado: 20-06-07]
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NON-BREEDING FEEDING ECOLOGY OF BONELLI´S EAGLES 143