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ORIGINAL PAPER
The role of pigeon consumption in the population dynamics
and breeding performance of a peregrine falcon
(Falco peregrinus) populatio n: conservation implications
Pascual López-López & José Verdejo & Emilio Barba
Received: 18 February 2008 /Revised: 7 August 2008 /Accepted: 16 September 2008 /Published online: 7 October 2008
#
Springer-Verlag 2008
Abstract In this paper, we describe and analyze the diet of
peregrine falcons during a long-term period (1982–2002).
A combination of direct observations of prey brought to
nests, prey remains, and regurgitated pellets were used to
calculate diet diversity and dietary overlap between
peregrine pairs. We also examined diet diversity in relation
to breeding performance. All peregrine pairs fed mainly on
birds, with pigeons the most common prey. An increase in
pigeon availability has been associated with both an
increase in population size and an increase in breeding
performance (measured as the average productivity of pairs
per year) of a small peregrine falcon population in eastern
Spain. Average productivity was lower when dietary
breadth was higher. We speculate that our resul ts were the
synergistic effect of declining persecution and increased
pigeon availability through increased popularity of keeping
racing pigeons. There is a conflict of interests between
pigeon fanciers and peregrine conservation. As a conse-
quence, this could result to an increased risk of mortality by
direct persecution. In accordance with this, conservation
measures aimed at preventing direct persecution are
encouraged.
Keywords Diet
.
Castellón
.
Homing
.
Pigeon fancying
.
Raptors
.
Spain
Introduction
The peregrine falcon Falco peregrinus is the most widely
distributed raptor. In the Mediterranean region, the subspecies
occurring is F.p. brookei (Cramp and Simmons 1980;Del
Hoyo et al. 1994). With a preferentially avian-based diet
(Ratcliffe 1993; Monneret 2000), there are several reported
cases of hunting on mammals, insects, and even fishes
(Zuberogoitia et al. 2002). Actually, its capacity to prey on
species of human interest has caused a traditional rejection by
some sectors of the society, especially those related with
human economic interest. In the Spanish Mediterranean
region, similar to other regions of Southern Europe, pigeon
fancying has become a traditional activity which is very
deep-routed, with its origins going back to the Muslim
occupation of Spain in the eight century (Mínguez et al.
2005). As peregrines can prey on racing pigeons, it gives rise
to a clear conflict of interest among pigeon fanciers and
peregrine conservation, especially accentuated with those
pairs located closer to human populated areas (Ratcliffe
1993; Dixon et al. 2003). Then, it is interesting to clearly
describe and analyze the diet of peregrines in such areas and
to implement reliable con servation measure s aimed at
preventing a potential conflict.
In this paper, we describe and analyze the diet of a small
population of peregrine falcons located at the East of Spain
combining the use of three methods: (1) direct observations
of prey brought to nests, (2) collection of prey remains, and
(3) collection of pellets during a long-term period. We
examine the effect of changes in the diet in relation to the
observed duplication of the population size. Furthermore,
Eur J Wildl Res (2009) 55:125–132
DOI 10.1007/s10344-008-0227-2
Communicated by C. Gortazar
P. López-López (*)
:
E. Barba
“Cavanilles” Institute of Biodiversity and Evolutionary Biology.
Terrestrial Vertebrates Group, University of Valencia,
Polígono de la Coma s/n,
46980 Paterna, Valencia, Spain
e-mail: Pascual.Lopez@uv.es
J. Verdejo
Department of Microbiology and Ecology. Ecology Unit.
Facultad de Ciencias Biológicas, University of Valencia,
Campus de Burjassot. C/Doctor Moliner 50,
46100 Burjassot, Valencia, Spain
some descriptive parameters of dietary composition like
prey diversity, dietary breadth, and dietary overlap among
pairs are calculated. Additionally, we also examine diet
diversity in relation to breeding performance.
Materials and methods
Study area
The study area was loca ted in ea stern Spain, in the
southwest of Castellón province, including the Alto
Palancia and half of the Alto Mijares districts (40°08′ N,
39°43′ S, 0°26′ E, 0°50′ W; Fig. 1). This area encompasses
1,500 km
2
and ranges from 300 to 1,400 m a.s.l. and is
characterized as Mediterranean climate. For a complete
description of the study area, see Verdejo (1991, 1994) and
Verdejo and López-López (2008). The study was conduct ed
between 1982 and 2002 during each breeding season (from
early February to the end of July).
Numerous papers have tested different methods to assess
the diet in raptors (Martí 1987; Simmons et al. 1991) and
particularly in peregrine falcons (Oro and Tella 1995).
These methods include (1) direct observation of prey
hunting, (2) observation of prey contribution to the nest,
(3) collection of prey remains, and (4) collection of pellets
(the regurgitated, indigestible body parts of preys; Dekker
1980; Bird and Aubry 1982; Thiollay 1982). For this study,
we have employed the last three methods, given that the
combination of them has been sugges ted as a good estimate
of peregrine’s diet (Oro and Tella 1995).
For the detection of breeding pairs, direct searches for
nesting places were conducted, and all known breeding
places and potential ones were visited (Ratcliffe 1993).
Observations were made ≈300 m from cliff nest sites with a
20–60× spotting scope during clear days to avoid disturbance
to falcons. A territory was considered occupied if we observed
nests with hollows, typical pair behavior, courtship, brood
rearing activity, or young (Newton 1979; Steenhof and
Kochert 1982). We considered as the same pair those that
occupied the same breeding place during all years or at least
one part of the study period, although presumably, some
individuals conforming breeding pairs could have changed.
Dietary data of at least 5 years for each pair was obtained,
except for one new pair settled in 2002 which only data for
this year were available, excluding them from the analysis.
Data on number of prey items recorded per pair, monitored
years, breeding performance (measured as average produc-
tivity per pair per year), distance to nearest neighbor, and
distance to nearest village were recorded for all the pairs in
the study area.
All nest sites and frequently used roosting places were
visited to collect pellets and abandoned prey remains during
the breeding season. In addition, in order to minimize the
bias of pellets and prey remains in the composition of the
peregrine diet, we also conducted direct observations of prey
contribution to the nests (Dekker 1980; Bird and Aubry
1982;Thiollay1982; Oro and Tella 1995). Data from the
three sources were pooled together for the analyses. It might
be possible that some minor duplication could have occurred
because the same prey item may have been recorded by each
of the three methods. At least three visits were made to each
pair during the breeding period, with an average duration of
240 min per visit. Prey items were identified to species level
by comparison to field guides and a private collection of
bones and feathers owned by the second author. In several
cases, principally in pellet analysis, prey identification to
species level was impossible, and data were grouped as a
single category named “unidentified passerines”.Thisgroup
was deducted in the sum of species richness for each pair.
Prey biomass was estimated according to Cramp et al.
(1977–1985) and Jutglar and Masó (1999).
Prey diversity
We calculated the Gini index of diversity (Gotelli and
Ellison 2004) instead of other commonly used indexes of
diversity (e.g., the Shannon–Weiner index) because it does
not confound species richness and evenness and especially
because of its lack of dependence on sample size (Gotelli
and Graves 1996; review in Magurran 2003). This index is
used taxonomically at species level, and similarly to other
indexes, the higher the index value, the higher the diversity
measure (Gotelli and Graves 1996).
The index was calculated as:
G ¼ 1
X
n
i¼1
p
2
i
Fig. 1 Iberian Peninsula with the Castellón province shaded. In box:
Castellón province. The study area is shaded in gray
126 Eur J Wildl Res (2009) 55:125–132
where p
2
i
is the square of the proportion of each prey item i
in the sample.
Dietary breadth
Dietary breadth allows measuring how diverse the peregrines’
diet is. This is similar to the Gini prey diversity index, but in
this case, prey items are grouped by taxa higher than the
species level (family, order, etc.). Dietary breadth was
calculated following Steenhof and Kochert (1985)onthe
basis of the formula proposed by Levins (1968). According to
them, dietary breadth was calculated as:
B ¼ 1
.
X
p
2
i
where p
2
i
represents in this case the square of the proportion of
the diet contributed by the ith taxon. Values for this index
range from 1 to ∞. For consistency, prey taxa were grouped
by family for birds and mammals and for order for reptiles,
allowing comparisons among pairs (Watson 1997). In both
prey diversity and dietary breadth indexes, unidentified
passerines were treated as a single category.
Dietary overlap
The dietary overlap among breeding pairs was calculated
by means of the Pianka’s overlap index (Pianka 1973). A
null model of dietary overlap was performed using the
“niche overlap ” module of the freely available EcoSim v7.0
software (Gotelli and Graves 1996; Gotelli and Entsminger
2001, www.garyentsminger.com). It allowed us to test if the
observed dietary overlaps differ from that expected by
chance (Sale 1974;Schoener1974;IngerandColwell1977).
A randomization algorithm was performed retaining the
dietary breadth of each pair, but randomizing which
particular resource states was utilized. Following Lawlor
(1980), it would correspond to a randomization algorithm of
type 3, and it is especially recommended to study dietary
niche overlap when all resources are all potentially available
(in our case, it means that there is no biological constraints
preventing peregrines consumption from any class of prey;
Gotelli and Graves 1996). This index was used taxonomi-
cally at species level. A complete review of the advantages
and potential applications of this method are available in
Haefner (1988)andWinemillerandPianka(1990).
Pigeon availability
Pigeon availability was estimated by interviewing pigeon
fanciers of the municipalities included in study area. We
also obtained data from the Spanish National Institute of
Statistics (www.ine.es). Pigeons were classified as wild
birds (including Columba livia, C. oenas, C. palumbus,
Streptopelia decaocto, S. turtur), racing birds, strays (birds
that have been lost and not returned to lofts), and ferals
(birds that have been incorporated into the wild population).
We gathered information about number of pigeon fanciers’
clubs, year of creation, initial and current number of pigeon
fancying licenses, and presence of “pigeon barriers” (pigeon
lofts built to prevent falcons and eagles from attacking racing
pigeons) in the vicinity of the nesting areas. The number of
flying days per week, number of flying pigeons per day, and
number of racing pigeons per competition were also
obtained.
Statistical analysis
Differences in diet composition among pairs were tested by
means of chi-square tests on contingency tables. Non-
parametric correlations were performed to examine the
effect of changes in the proportion of pigeon consumption
by year in relation to changes in the peregrine population
size and between the average productivity (calculated as
fledged chicks/ number of years of occupied territory) of
peregrine’s pairs and the percentage of pigeons in the diet.
In addition, to test how the diversity of their diet affects
peregrines’ breeding performance, a non-par ametric corre-
lation was performed between the average productivity and
the dietary breadth of each pair. All computations were
performed using STATISTICA version 7.0 for Windows
(StatSoft
2004). Statistical significance was set at P<0.05.
Results
Population size of peregrines almost doubled during the
study period, starting with five pairs until a maximum of
nine pairs in 2002. In relation to dietary analysis, 42% of
data came from pellet collection, 22% from direct observa-
tions, and 36% from prey remains collected in nests and
roosting places (N=820; Table 1). Overall the diet was
Table 1 Descriptive parameters recorded for the nine pairs of
peregrine falcon in the study area
Pair
no.
Prey
items
Monitored
years
Average
productivity
(chicks/year)
Distance to
nearest
neighbor (m)
Distance
to village
(m)
1 132 21 2.29 5,800 3,800
2 93 20 2.35 6,160 3,600
3 91 19 2.63 8,450 7,300
4 136 16 2.17 8,450 3,500
5 112 21 2.55 3,650 3,000
6 68 6 2.40 6,160 2,000
7 84 6 2.00 3,650 2,000
8 54 5 2.60 1,300 1,500
9 50 5 2.60 9,150 3,000
Eur J Wildl Res (2009) 55:125–132 127
essentially composed by birds, accounting for 99.15% of
the prey items fro m at le ast 35 differe nt species (Tab le 2).
Six mammals were detected as a prey, including four
rabbits, Oryctolagus cuniculus, and two undetermined
bats (probably Myotis or Rinholo phus spp.). We also
could observe the contribution to the nest of one ladder
snake (Rinechis scalaris)50cminlengthapproximately.
Average prey mass weighted according to its frequency
in the diet was 204.79 g (range=9–1,200, N=820). The
Gini index of diversi ty range d from 0.73 to 0.88 ( mean=
0.83, SD=0 .05). Niche breadth ranged from 2.32 to 5.00
(mean=3.81, S D=0.95). Average dietary ove rlap was
0.93 (range=0.84–0.97), higher than that expected by
chance (expected die tary overlap=0.17, P<0.000 1).
Among bird preys, the family Columbidae accounts for
43.78% of the diet by number of individuals and 68.69% by
mass. Within Columbidae, 69.70% of the bioma ss corre-
sponds to rock pigeon, Columba livia (N=268 items), with
the rest corresponding to common wood pigeon, Columba
palumbus (19.90%) and stock dove, Columba oenas
(10.40%). There were no differences in the proportion of
pigeon consumption among pairs (χ
2
=0.089, df=8,
P>0.05), showing that all peregr ine pairs prey mainly on
this family. More interestingly, the proportion of pigeons in
the diet was positively associated with peregrine numbers
(Spearman r=0.79, P<0.001, N=21; Fig. 2) and average
productivity (Spearman r=0.66, P=0.052, N=9), this in the
threshold of significance. Conversely, average productivity
Table 2 Summary of the diet
of peregrine falcons in eastern
Spain (1982–2002), as esti-
mated by direct observations,
pellets, and prey remains
Rows are organized in
descending percentage of prey
by mass
a
An average of 30 g/item was
used to obtain the % of prey
mass (Cramp et al. 1977–1985)
b
Mammals
c
Reptile
Prey type Number of items % number of preys % prey mass
Rock pigeon, Columba livia 268 32.68 47.88
Common wood pigeon, Columba palumbus 51 6.22 13.67
Magpie, Pica pica 64 7.80 8.19
Stock dove, Columba oenas 40 4.88 7.15
Partridge, Alectoris rufa 19 2.32 5.43
Spotless starling, Sturnus unicolor 47 5.73 2.38
Unidentified passerines
a
125 15.24 2.23
Rabbit, Oryctolagus cuniculus
b
4 0.49 2.14
Eurasian turtle dove, Streptopelia turtur 24 2.93 2.00
Hoopoe, Upupa epops 44 5.37 1.76
Blackbird, Turdus merula 22 2.68 1.05
Eurasian jackdaw, Corvus monedula 7 0.85 1.00
Collared dove, Streptopelia decaocto 6 0.73 0.71
Common pheasant, Phasianus colchicus 1 0.12 0.71
Little owl, Athene noctua 6 0.73 0.63
Green woodpecker, Picus viridis 5 0.61 0.54
Common krestel, Falco tinnunculus 3 0.37 0.37
Sky lark, Alauda arvensis 12 1.46 0.29
Common swift, Apus apus 12 1.46 0.29
Rock sparrow, Petronia petronia 14 1.71 0.25
Song thrush, Turdus philomelos 5 0.61 0.21
Moorhen, Gallinula chloropus 1 0.12 0.19
Great spotted cuckoo, Clamator glandarius 2 0.24 0.18
Crested lark, Galerida cristata 6 0.73 0.16
Common quail, Coturnix coturnix 2 0.24 0.12
Greenfinch, Carduelis chloris 5 0.61 0.08
Blue rock thrush, Monticola solitarius 2 0.24 0.07
Mistle thrush, Turdus viscivorus 1 0.12 0.07
House sparrow, Passer domesticus 4 0.49 0.07
Goldfinch, Carduelis carduelis 6 0.73 0.05
Black redstart, Phoenicurus ochruros 5 0.61 0.05
Eurasian crag martin, Ptyonoprogne rupestris 3 0.37 0.04
Black wheatear, Oenanthe leucura 1 0.12 0.02
Ladder snake, Rinechis scalaris
c
1 0.12 0.01
Bat spp.
b
2 0.24 0.01
Total 820 100 100
128 Eur J Wildl Res (2009) 55:125–132
was lower when dietary breadth was higher (Spearman
r=−0.90, P=0.002, N=9).
Discussion
Direct observation of prey hunting and observation of prey
contribution to the nest has been suggested as the best
method to determine the diet of peregrine falcons (Dekker
1980; Bird and Aubry 1982; Thiollay 1982). However,
these methods require a great deal of time, and studies
based only on them are scarce (Marti 1987). Usually, diet
studies on peregrine falcon have been based on the
collection of prey remains and pellets, but they are blamed
for bias in the analysis of diet (Mearns 1983). Whereas
pellet analysis tend to overestimate consumption of small to
medium-sized preys, studies based on prey remains tend to
overestimate the consum ption of large-size preys (Mearns
1983; Oro and Tella 1995; Zuberogoitia et al. 2002). In this
study, we have combined the use of all methods aforemen-
tioned in order to minimize the possible bias, as demon-
strated by several authors (Collopy 1983; Simmons et al.
1991; Mersmann et al. 1992; Mañosa 1994; Oro and Tella
1995; Zuberogoitia et al. 2002). However, other methods
like video recording directly at nest sites could also be used
(Margalida et al. 2006; review in Reif and Tornberg 2006;
López-López and Urios, submitted).
Peregrines can prey on preys lower than 10 g up to preys
larger than them and over 1,200–1,500 g (Ratcliffe 1993).
This author estimated the optimal prey mass around
100–150 g depending on factors like sex, temperature,
health status, experience, etc. (Ratcliffe 1993; Jenkins and
Avery 1999). Other authors estimate 188 g of prey mass per
day necessary for an adult and calculated a prey delivery
rate of 222 g per nestling (and dependent fledgling) per day
(Redpath and Thirgood 1997). In any case, pigeons with an
average mass of 300–450 g are above the optimal prey
mass. Our results show that peregrines prey mainly on
pigeons without differences among pairs in the proportion
of this type of prey in the diet. Similar results have been
found in other studies of this species, showing the key role
of pigeons in the peregrine’sdiet(reviewinValkamaetal.
2005). For example, pigeons represent nearly 50% in the diet
by number in UK (Ratcliffe 1993) and Scotland (Mearns
1983; Redpath and Thirgood 1997) and even 57.8% in
France (Bayle 1981). It has been suggested that peregrines
would tend to a generalization in prey consumption as the
climate become s more extreme (e. g., tundra, deserts),
whereas they would tend to specialization in regions with a
temperate climate (Jenckins and Avery 1999). Our results
might support this prediction, taking into account the high
proportion of pigeon in the diet (in some cases representing
more than 50% of prey items detected). However, another
explanation is that peregrine falcons prey according to prey
availability (Ratcliffe 1993;Zuberogoitiaetal.2002), or
even that some pairs could have a preference for a certain
class of prey (Thiollay 1988; Rosenfield et al. 1995).
In our study area, pigeon availability has notably
increased from the eighties. This increase is related with
the increase in pigeon fancying licenses and the creation of
new pigeon fanciers’ clubs (Mínguez et al. 2005). Unfor-
tunately, even though we could not tag racing pigeons to
conduct a specific study on the impact of peregrines on this
type of prey, the general increase of the number of pigeon
fancying licenses and pigeon fanciers’ clubs can be taken as a
Table 3 Summary of the pigeon fancying activity in six municipalities of the study area
Municipality Population
a
Pigeon
societies
Year of
creation
Initial
licenses
Licenses in
2005
Pigeon
barriers
Flying days/
week
Pigeons/
day
Pigeons/
competition
Segorbe 8,023 1 1965 3 47 1 7 150 200
Jérica 1,561 1 1990 4 11 3 3 60/80 90
Altura 3,140 1 1975 5 40 2 4 100 100
Soneja 1,383 1 1980 1 5 2 4 60 90
Castellnovo 1,026 1 1980 2 23 2 4 90 90
Sot de Ferrer 407 1 1980 No data No data No data 3 70 90
Data were obtained by interviewing pigeon fanciers directly and kindly provided by Mínguez et al. (2005)
a
Data taken from the Spanish National Institute of Statistics (www.ine.es)
Fig. 2 Relationship between pigeon consumption and the observed
duplication of population size between 1982 and 2002
Eur J Wildl Res (2009) 55:125–132 129
proper surrogate on the increase of pigeon availability in our
study area (Table 3). Currently, there are 953 pigeon fancying
licenses and 40 clubs in the whole Castellón province. More
specifically, for example, in the municipalities included in
the study area, there are flying nearly 100–150 pigeons per
training day, and nearly 2% of these pigeons are lost every
day, becoming available for falcons (data provided directly
by the pigeon fanciers; Table 3).
Our results suggest that an increase in pigeon availability
has been associated with both an increase in population size
and an increase in breeding performance of a peregrine
falcon population in eastern Spain. From our point of view,
this could be explained as the synergistic effect of a decline
in direct persecution, consequence of the publication of the
Spanish Law of protection of wild Flora and Fauna in 1989
(Law 4/89) and the Valencian Law of Protection of Natural
Areas in 1994 (Law 11/94), and a slight but continuous
increase of pigeon availability in the study area. As pigeon
availability increased, its proportion in the diet also did the
same, decreasing the dietary breadth. According to Watson
(1997), analyzing golden eagle’s(Aquila chrysaetos) diet,
raptors should be more successful when they can concen-
trate on hunting few prey species which lie in the bird’s
optimal size range. This could also explain the higher
breeding per formance observed in the study area, in
contrast to that reported in other parts of the world
(J. Verdejo and P. López-López 2008).
Conservation implications
In some European r egions, p igeon f ancie rs perceiv e
raptors as the main cause of losses, demanding political
measures to control peregrine numbers actively or even
persecuting peregrines to a significant degree. In these
areas, estimating the predation on racing pigeons (as
opposed to birds which have strayed, birds which have
gone feral, or wild pigeons) becomes an important issue.
Racing birds, strays, and feral s are usually ringed.
However, it is difficult to distinguish among these
different types of pigeons in the diet without conducting
a specific sampling design, as in our case. Thus,
although we collected a high number of rings, we were
unfortunately unable to calculate the proportion of the
different pigeon types exactly (feral, racing, strays, or
wild). Anyway, recent studies have demonstrated the
strong limitations of using ring recoveries to evaluate the
impact of peregrine kills on racing pigeons (Parrott et al.
2008).
The increase in pigeon fanciers has been focused in large
villages within the study area. This phenomenon brings
peregrine falcons closer to populated places in their hunting
search. This situation becomes worse provided that the
majority of competitions take place from Dece mber to May,
overlapping with the period when peregrines start to breed
in the region and have a corresponding higher need of prey
intake. This result corresponds with that reported in UK
where the increase and decrease in the pigeon component
of the diet coincides with the start and end of the racing
pigeon season respectively, indicating the importance of
racing pigeon s (or strays or ferals) as a food supply (Dixon
et al. 2003). Taking into account the fact that racing pigeons
could reach a value up to 10.000€ , this could cause a
conflict of interests between peregr ines and pigeon fanciers.
As a consequence, this could result to an increased risk of
mortality by direct persecution. Furthermore, another threat
to falcon s (an d other raptors suc h as the endangered
Bonelli’s eagle Aquila fasci ata) is the transmission of
diseases from pigeons to raptors, such as trichominiasis,
caused by the flagellated protozoon Trichomonas gallinae
(Höfle et al. 2004; Villanúa et al. 2006; Hegemann et al.
2007). In accordance to these, conservation measures aimed
at preventing direct persecution and disease transmission
are encouraged.
Finally, there are few reported studies aimed at quanti-
fying the effect of raptor predation in racing pigeons (but
see Henderson et al. 2004 and Parrot et al. 2008). Although
not conclusive, there is no evidence that birds of prey cause
large-sc ale los ses of racing pigeons (Henderson et al.
2004). For example, Parrot et al. (2008) estimated that
peregrine kills based on “daily food intake”
represented 13–
40% of total losses of Scottish racing pigeons to all causes.
On this subject, it would be interesting to perform a long-
term study of the likely impact of peregrines and other
raptors on racing pigeons in the Mediterranean region.
Here, the unique study made shows that the perception of
local pigeon fanciers of raptors as a risk for pigeon losses
figures as the fourth of five causes of concern, after
collisions with power lines and cables, losses caused by
“wild” pigeons, terrestrial predators, and only before
natural diseases (Mínguez et al. 2005). An additional study
specifically aimed at d eterm in ing the effectiveness of
“pigeon barriers” would also be necessary. To date, this
has been the only measure implemented by the local
administration, even though the likely counterproductive
effects like raptor habituation to have pigeons as an easy-to-
capture prey have not been determined. Future research
ought to include such long- term specific analysis.
Acknowledgments We would like to thank everybody who helped
in the field work. Juan Manuel Pérez of the University of Elche kindly
provided unpublished data about their study of pigeon fancying in the
Valencian Community. Gary Entsminger kindly helped with niche
overlap calculations. Clara García, Álvaro Soutullo, Miguel Ángel
Gómez and Phillip Whitfield improved the English and made valuable
comments on an early draft of the manuscript. P. López-López is
supported by FPU grant of the Spanish Ministerio de Ciencia e
Innovación (reference AEP2005-0874).
130 Eur J Wildl Res (2009) 55:125–132
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