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INTER-LOCALITY VARIATION IN BREEDING PHENOLOGY
AND NESTING HABITAT OF THE CITRIL FINCH CARDUELIS
CITRINELLA IN THE CATALONIAN PRE-PYRENEES
Marc Imanuel FÖRSCHLER* ** *** 1, Antoni BORRAS*, Elisabeth K. V. KALKO**,
Josep CABRERA*, Toni CABRERA* and Juan Carlos SENAR*
SUMMARY.—Inter-locality variation in breeding phenology and nesting habitat of the citril finch Car-
duelis citrinella in the Catalonian Pre-Pyrenees.
Aims: Considerable variations have been found amongst several citril finch sub-populations at Port del
Comte mountain in the Catalonian Pre-Pyrenees in reproductive success, body mass, fat score, diet, sur-
vival rate and speed of moult due to different habitat quality and different slope exposition. In line with
these studies, the aim of this study was to investigate variations in breeding phenology and nesting habi-
tat between north-facing high quality areas (Vansa) and south-facing low quality areas (Bofia) as well as
east-facing areas of intermediate quality (Port Comte / Sucre). Since the species habitat requirements have
been little studied before, another aim of this study was the recording of some basic data on the phenolo-
gy of this species and its nesting habitat in Spain.
Location: The slopes of Port del Comte mountain (Catalonian Pre-Pyrenees).
Results and Conclusions: As expected, variations were found in breeding phenology and nesting habi-
tat. Birds on the moister and cooler north-and east-facing slopes (Vansa, Port Comte) started breeding ear-
lier than did birds from the drier and sunnier south-facing slopes (Bofia). All nests at the slightly more
elevated locality of Bofia were built in mountain pines Pinus mugo, while at the other two study sites a
small proportion of the nests were also situated in scots pines Pinus sylvestris. Nests were built mainly in
the top of the trees or in large side branches at a similar height above ground. At Bofia solitary trees were
more often used instead of tree groups or forest than at the other sites. Furthermore, nests were situated
at greater distance from each other and the proportion of subadult birds with breeding activity was high-
er at Bofia.
Key words: Citril f inch, Carduelis citrinella, breeding phenology, nesting habitat, inter-locality variation.
RESUMEN.—Variación entre localidades en la fenología reproductiva y en el hábitat de nidificación en
el verderón serrano Carduelis citrinella en los pre-pirinéos catalanes.
Objetivos: Con anterioridad, se han encontrado considerables variaciones entre distintas subpoblacio-
nes de verderón serrano en el Port del Compte (pre-pirinéos catalanes), en éxito reproductor, peso cor-
poral, grasa corporal, dieta, probabilidad de supervivencia y en la velocidad de muda. Estas diferencias
se deben por una lado a diferencias en la calidad del hábitat, y por otro a diferencias en la exposición de
la ladera de la montaña. En línea con estos resultados previos, el primer objetivo de este estudio fue estu-
diar las variaciones en la fenología reproductiva y en el hábitat de nidificación entre la pendiente norte
que representa un hábitat de alta calidad (Vansa) y la pendiente sur que representa un hábitat de baja ca-
lidad (Bofia), teniendo como población intermedia una población localizada en la ladera este de la mon-
* P. Picasso s/n, Parc Ciutadella, Museu Ciències Naturals, E-08003 Barcelona, Spain.
** Max Planck Research Centre for Ornithology, Vogelwarte Radolfzell, G-78315 Radolfzell,
Germany.
*** University of Ulm, Department of Experimental Ecology, D-89069 Ulm, Germany.
1Corresponding author: Marc.Firerscgker@biologie.uni-ulm.de
Ardeola 53(1), 2006, 115-126
INTRODUCTION
The distribution of the citril finch Cardu-
elis citrinella is in the boreal mountain zones
of western temperate Europe (Cramp and Per-
rins, 1994). Some of the highest breeding den-
sities are found in the Pyrenees (Baccetti and
Märki, 1997). Most birds nest in loose
breeding groups of 5 to 25 pairs. Characteris-
tically, there are often unoccupied areas be-
tween breeding spots of the species, which are
in potentially suitable habitats (Förschler,
2002a; Dorka, 1986; Glutz von Blotzheim and
Bauer, 1997). The population of the Port del
Comte mountain in the Catalonian Pre-Pyre-
nees was estimated in 2002 to be about 1200
to 2400 citril finch pairs, based on estimates
of settlement densities in sample areas. This
makes it one of the most densely settled areas
of the species in Spain (Borras and Senar,
2002; Borras et al., 2005).
The slopes of Port del Comte mountain show
an important bioclimatical contrast between
hygrophilous and cooler north-facing, and more
xerophyllous and sunnier south-facing facing
slopes (Gutiérrez, 1991; Borras and Junyent,
1993). In over 10 years of capture-recapture
studies at Port del Comte mountain, Senar et
al. (2002) and Borras et al. (2004) found no-
table differences in the speed of moult, body
condition, survival rate and wing morphology,
as well as asymmetric population exchange be-
tween the two subpopulations located on the
same mountain at a distance of only 5 km
(Senar et al., 2002). Furthermore, birds at the
north-facing locality (Vansa) were found re-
cently to rely more on mountain pine seeds Pi-
nus uncinata than birds on the south-facing lo-
cality (Bofia), which feed more on a series of
herb seeds (Borras et al., 2003). Finally,
these differences in inter-locality variation man-
ifest themselves also in significant variations
in reproductive success between the breeding
groups of north-facing Vansa with high suc-
cess, and south-facing Bofia with low breed-
ing success (Förschler et al., 2005).
Since habitat quality is known to differ con-
siderably between the various areas at Port del
Comte mountain (Gutiérrez, 1991; Borras and
Junyent, 1993; Senar et al., 2002; Borras et al.,
2003), it may be supposed that those environ-
mental conditions may also have effects on
breeding phenology and nest habitat of the
species. Furthermore, up to now, the nesting
habits of citril finches have been rarely stud-
ied. Therefore, analysis was carried out of data
FÖRSCHLER, M. I., BORRAS, A., KALKO, E., CABRERA, J., CABRERA, T. AND SENAR, J. C.
Ardeola 53(1), 2006, 115-126
116
taña (Port Comte / Sucre). Debido a que los requerimientos de hábitat han sido poco estudiadas, el se-
gundo objetivo del presente estudio fue el registrar los datos básicos de la fenología reproductora y el há-
bitat de nidificación de esta especie en España.
Localidad: Las laderas del Port del Comte (pre-pirinéos catalanes).
Resultados y Conclusiones: Como era esperado, se encontraron diferencias en la fenología reproduc-
tora y el hábitat de nidificación entre las distintas poblaciones estudiadas. Las parejas que se reproducen
en la ladera norte y este, que presentaban un mayor grado de humedad y una temperatura menor (Vansa,
Port Comte) iniciaban su reproducción antes que las parejas situadas en la ladera sur (Bofia) que es más
seca y soleada. Todos los nidos de Bofia se encontraron en Pinus mugo, mientras que en las otras locali-
dades hubo un porcentaje de nidos tambien situados en Pinus sylvestris. Los nidos se situaron principal-
mente en la parte alta de los árboles o en las ramas laterales grandes a una altura similar. En Bofia, en com-
paración con las otras localidades, se utilizaron más frecuentemente los árboles solitarios que los grupos
de árboles. Además, en esta localidad, los nidos se encontraron a mayor distancia entre sí y el porcentaje
de subadultos reproductores fue mayor que en las otras poblaciones estudiadas.
Palabras clave: Verderón serrano, Carduelis citrinella, fenología reproductora, habitat de nidificación,
variación entre localidades.
on the breeding phenology and nesting habitat
of citril finches, these data obtained during a
study on reproductive success (Förschler et al.,
2005) at the three localities of Port del Comte
mountain: Vansa (north-facing slope), Bofia
(south-facing slope) and Port Comte / Sucre
(east-facing slope).
MATERIAL AND METHODS
Searching for nests
Between April and June 2002, citril finch
nests were searched for systematically during
nest building time on three localities of Port
del Comte mountain. These comprised the
north-facing slope at the skiing resort Vansa /
Prat Llong, a high-quality locality (Senar et al.,
2002), the south-facing slope of Bofia, a low-
quality locality (Senar et al., 2002) and the east-
facing slope of Port Comte as well as the ski-
ing area Sucre, areas of intermediate quality
for citril finches (Förschler et al., 2005). Most
nests were found by following the females that
were engaged in nest building.
Nest parameters
When a nest was found, the following pa-
rameters were noted: slope inclination, eleva-
tion, tree species, height, shape of tree, posi-
tion and structure of nest, nest height, distance
of nest to main trunk and to end of nest branch,
exposition of nest and nesting tree, slope incli-
nation at the nesting site, beginning of nest
building (pentad), first, second or repeat clutch,
and age of nesting birds. For each nesting site
the following parameters of the nest surround-
ing were documented as well: distance of the
nest to permanent water resources, salt uptake
places and important food sources, distance to
open space, to tracks and forest edges, as well
as distance to simultaneously used nests of
neighbouring pairs.
Age combination of nesting pairs
Whenever possible, the age of nesting birds
was determined, especially during nest build-
ing, by means of typical plumage marks.
Subadult birds (2nd calendar year) can be
distinguished under good observation condi-
tions from adult birds (3rd calendar year or old-
er) by the whitish coloration of some greater
wing coverts (Jenni and Winkler, 1994; Glutz
von Blotzheim and Bauer, 1997).
Statistical analysis
Statistical comparison was carried out be-
tween the three study sites. If the data was dis-
tributed parametrically, ANOVA was used. If
the data showed no parametric distribution,
Kruskal Wallis Anova was used and Dunn’s
pairwise multiple comparison procedure car-
ried out to detect statistical differences between
groups.
RESULTS
A total of 72 nests was found on the three
slopes of Port del Comte mountain, including
14 nests on the south-facing slopes of Bofia
(Refugi, Canalda), 24 nests on the north-fac-
ing slopes of the skiing resort Vansa (L’Arp,
Prat Llong) and 34 nests on the east-facing
slope of the skiing resort Porte del Comte / Su-
cre (Forat de Bofia, Prat de Botons, Rasa de
Bofia, golfing area and around the hotels).
Nest building activity showed two peaks,
with a first maximum in pentad 22 (f irst breed-
ing; 16.04.-20.04.) and a second maximum in
pentad 30 (second and repeat breeding; 26.05.-
30.05.) (Fig. 1). The proportion of second and
repeat clutches was with more than 40 % at the
south-facing slope (Bofia), nearly twice as high
as on north- and east facing slopes (Fig. 3).
Mountain Pine was the tree species mainly
selected where citril finch nests were built.
Ardeola 53(1), 2006, 115-126
BREEDING PHENOLOGY AND NESTING HABITAT OF THE CITRIL FINCH 117
However a small number of nests were found
in scots pine as well, at Vansa (4 %) and at Port
Comte (15 %). Nesting sites were allocated
to four groups concerning position of nesting
tree from single trees to closed forest. Bofia
had a much higher percentage of nests in sin-
gle trees than did Vansa and Port Comte (Fig.
4). Port Comte nests were situated more often
in tree groups than were nests in the other
two areas. In Vansa half of all nests were situ-
ated at forest edges and in forests. Furthermore,
Vansa had a higher percentage of nests locat-
ed in trees with a single trunk than nests in
the other two areas (Fig. 5).
Several nest parameters were obtained, in-
cluding time of nest building, slope inclina-
tion, nest height, nesting tree height, distance
to permanent water and food resources, to open
space, to human trails, to forest edge, as well
as the distance to simultaneously used nests of
neighbouring pairs. Data of statistical compar-
isons are summarised in Table 1.
There was a significant difference in time
of first nest building between south-facing
(Bofia) and north-facing (Vansa) localities, but
no significant differences between north- and
east-facing (Port Comte) localities. Nests at
the south-facing locality were built at higher
elevations than nests at north- and east-facing
slopes in Vansa and Port Comte. Inversely, nests
at east-facing Port Comte were built in an area
with a much steeper slope (inclination) than
were nests in areas of Vansa and Bofia. Differ-
ences, however, were not significant. Nearly
FÖRSCHLER, M. I., BORRAS, A., KALKO, E., CABRERA, J., CABRERA, T. AND SENAR, J. C.
Ardeola 53(1), 2006, 115-126
118
FIG. 1.—Nest building activities (n= 72) of citril finches Serinus citrinella in 22nd (16.04.-20.04.) to the
33th (10.06-14.06.) pentad at Port del Comte mountain. From pentad 30 (26.05.-30.05.) there was a
clear second peak due to new nest buildings after the main part of the juveniles of the early nests have
fledged out. The allocation of nest building activities to the second breeding mentioned between pentad
27 and 29 in the figure are the result of direct observation of nest building females which alternated be-
tween feeding young birds of the first breeding and, at the same time, building a new nest for the second
breeding close to the first nest (see also Förschler, 2001).
[Distribución de fechas de inicio de la construcción del nido en primeras y segundas puestas de verderón
serrano en el Port del Comte (n= 72). Las segundas puestas a partir del 26 de mayo se asignaron por
observación directa de hembras que construían nidos a la vez que cebaban pollos en otro nido o por ni-
dos construidos muy cerca de nidos en donde ya habían volado los pollos.]
Ardeola 53(1), 2006, 115-126
BREEDING PHENOLOGY AND NESTING HABITAT OF THE CITRIL FINCH 119
FIG. 2.—Nest building activities (n= 72) of citril finches Serinus citrinella in pentads at three slopes of
Port del Comte mountain.
[Distribución de las fechas de inicio del nido en el verderón serrano Serinus citrinella en las tres laderas
del Port del Comte (n= 72).]
FIG. 3.—Proportion of first and second/replacement nest building (n= 72) of citril finches Serinus cit-
rinella at Port del Comte mountain.
[Proporción de primeras y segundas puestas (o puestas de reposición) del verderón serrano Serinus ci-
trinella en las tres laderas estudiadas en el Port del Comte (n= 72).]
FÖRSCHLER, M. I., BORRAS, A., KALKO, E., CABRERA, J., CABRERA, T. AND SENAR, J. C.
Ardeola 53(1), 2006, 115-126
120
FIG. 4.—Proportion of nesting positions in citril finches Serinus citrinella (n= 72) with regard to habi-
tat type and tree grouping on three slopes of Port del Comte mountain.
[Localización de los nidos (porcentaje) de verderón serrano Serinus citrinella (n= 72) en relación al tipo
de hábitat (interior de bosque, límite del bosque) y de la agrupación del arbolado (arboles solitarios o en
grupo) en las tres laderas estudiadas en el Port del Comte.]
FIG. 5.—Allocation of citril finch Serinus citrinella nests (n= 72) to nesting tree type on three slopes of
Port del Comte mountain.
[Localización de los nidos (porcentaje) de verderón serrano Serinus citrinella (n= 72) en relación al tipo
de troncos (sencillos, dobles o múltiples) en las tres laderas estudiadas en el Port del Comte.]
Ardeola 53(1), 2006, 115-126
BREEDING PHENOLOGY AND NESTING HABITAT OF THE CITRIL FINCH 121
TABLE 1
Comparative characterization of breeding phenology and habitat selection of the three slopes at Port del
Comte mountain in 2002 (mean ± SD). ANOVA (F) is used for comparison of parametric distributed and
Kruskal-Wallis-Anova (H) and Dunn’s pairwise multiple comparison procedure (Dunn) for non-paramet-
ric distributed data. n= Sample size.
[Comparación de variables que caracterizan la fenología reproductora y del hábitat en las tres laderas
estudiadas en el año 2002 en el Port del Comte (media ± DT). Se uso un ANOVA (F), una prueba de Krus-
kal-Wallis (H) o una prueba a posteriori de Dunn dependiendo de la distribución normal o no de las va-
riables. n= tamaño de muestra.]
Variable Vansa Bofia Port Comte Statistical comparison
north-facing south-facing east-facing
First nest (start date) 24.8 ± 3.5 27.2 ± 3.1 25.4 ± 3.5 H= 42.52, df = 2, P< 0.001
[Inicio del primer nido] Dunn: P< 0.05 for Bofia vs.
Port Comte, and Vansa vs. Port Comte
Elevation (m a.s.l.) 1975 ± 64 2060 ± 23 1855 ± 37 H= 9.03, df = 2, P= 0.01
[Altitud (m s.n.m)] n = 24 n= 14 n= 34 Dunn: P< 0.05 for Bofia vs.
Port Comte, and Vansa vs. Port Comte
Slope inclination (degrees)13.1 ± 5.8 10.6 ± 4.5 15.3 ± 6.9 H= 9.03, df = 2, P= 0.06
[Pendiente (grados)] n = 24 n= 14 n= 34
Nesting tree height (m) 8.2 ± 2.4 7.4 ± 2.8 6.8 ± 2.0 F= 2.66, df = 2, P= 0.08
[Altura del árbol (m)] n = 24 n= 14 n= 34
Nest height (m) 5.9 ± 3.3 4.8± 2.9 4.6 ± 2.3 H= 2.25, df = 2, P= 0.33
[Altura del nido (m)] n = 24 n= 13 n= 34
Vertical position (%) 40 ± 10 39 ± 11 40 ± 9 H= 0.92, df = 2, P= 0.96
[Posición vertical (%)] n = 24 n= 13 n= 34
Horizontal position (%) 61 ± 37 59 ± 40 55 ± 38 H= 0.02, df = 2, P= 0.99
[Posición horizontal (%)] n = 22 n= 14 n= 33
Nearest closed forest (m) 18 ± 26 90 ± 149 64 ± 74 H= 6.39, df = 2, P= 0.04
[Bosque más cercano (m)] n = 24 n= 14 n= 34 Dunn: no sign.
Nearest human trails (m) 25 ± 25 71 ± 51 22 ± 29 H= 11.38, df = 2, P= 0.003
[Sendero más cercano (m)] n = 24 n= 14 n= 34 Dunn: P< 0.05 for Bofia
vs. Port Comte
Nearest Dandelion site (m) 33 ± 25 45 ±45 43 ± 37 H= 0.48, df = 2, P= 0.79
[Distancia al más cercano
Taraxacum (m)] n = 24 n= 14 n= 34
Nearest water source (m) 352 ± 308 288 ± 318 525 ± 332 H= 9.11, df = 2, P= 0.01
[Distancia al punto más Dunn: P< 0.05 for Bofia
cercano de agua (m)] n = 24 n= 14 n= 34 vs. Port Comte
Nearest salt place (in m) 491 ± 288 483 ± 684 1264 ± 590 H= 26.60, df = 2, P< 0.001
[Punto con sal Dunn: P< 0.05 for Bofia vs. Port
más cercano (m)] n = 24 n= 14 n= 34 Comte and Vansa vs. Port Comte
Nearest neighbour (m) 44 ± 20 60 ± 19 58 ± 30 F= 1.64, df = 2, P= 0.20
[Vecino más cercano (m)] n = 14 n= 9 n= 22
significant results were obtained concerning
the height of nesting trees with slightly high-
er nesting trees in north-facing Vansa than in
the other areas. No significant differences were
found concerning height of nests above ground
as well as in the vertical and horizontal posi-
tion of the nests in the trees.
A significant difference was detected for
birds in Vansa that nested closer to forest struc-
tures than did birds at Bofia and Port Comte.
Furthermore, birds at Bofia nested significant-
ly further away from the nearest human trails
than did the birds at the other two localities.
There was no significant difference among sites
regarding distance of nesting sites to impor-
tant food resources such as dandelion Tara x-
acum officinale, mountain pines and other herbs
and grasses. Citril finches at east-facing Port
Comte had to fly further to the nearest source
of permanent water and salt uptake sites in com-
parison with the other two sites. Finally, there
was no significant difference in distance to the
nearest nest of a neighbouring pair, although
birds at north-facing Vansa tended to nest some-
what closer to their nearest neighbours than did
birds at south-facing Bofia and east-facing Port
Comte.
In total more than two thirds of all age-de-
termined nesting birds were adults. The pro-
portion of birds in adult plumage was highest
in north-facing Vansa with more than 80 % and
lowest in south-facing Bofia with less than
60 % birds with adult plumage. At Port Comte
70 % of all birds were adults (Fig. 6). Regard-
ing mating of age-determined breeding pairs
(Fig. 7), in 66 % of all cases both partners were
adults, in 22 % both partners were subadults.
In 12 % an adult male mated with a subadult
female. No mating was observed between a
subadult male and an adult female. In Vansa,
an extraordinarily high proportion of adult-
adult mating occurred with more than 90 %,
whereas in Bofia only 40 % of all age-deter-
mined pairs were adult-adult pairs. Port Comte
was intermediate between Vansa and Bofia with
60 % adult-adult matings.
FÖRSCHLER, M. I., BORRAS, A., KALKO, E., CABRERA, J., CABRERA, T. AND SENAR, J. C.
Ardeola 53(1), 2006, 115-126
122
FIG. 6.—Age of breeding citril finches Serinus citrinella (n= 89) on three slopes of Port del Comte moun-
tain (adult: 3rd calendar year or older; subadult: 2nd calendar year).
[Composición de edades de los adultos reproductores de verderón serrano Serinus citrinella (n= 89) en
las tres laderas estudiadas en el Port del Comte.]
DISCUSSION
As previously expected, some variations
were found in breeding phenology and nesting
habitat between north-, east- and south-facing
breeding sites of citril finches at Port del Comte
mountain in the Catalonian Pre-Pyrenees, prob-
ably due to different bioclimatic conditions and
habitat qualities (Gutiérrez, 1991; Borras and
Junyent, 1993; Borras et al., 2003).
Nest building activity took place between
the 22nd and the 33rd pentad with two peaks,
a higher one in the 22nd pentad (first brood)
and a smaller one in the 30th pentad (second
brood). A major part of all nests was built dur-
ing a few days. This pattern can be explained
by the strong influence of weather conditions
on nest building. Citril finches started nest
building synchronously during the first warm
days. Similar observations have been made for
populations of citril finches in the Black For-
est (Förschler, 2002a). Synchronous nest build-
ing behaviour may help the birds to diminish
predation rate and enable them to exploit good
food conditions optimally within the breeding
groups (Newton, 1972). Birds of neighbour-
ing nests often use good food sources in the
surrounding collectively and synchronously.
Whereas birds in the high quality areas
(Senar et al., 2002) on north- and east-facing
slopes (Vansa, Port del Comte) started nest
building earlier, birds of the south-facing slope
(Bofia) showed a delay of two pentads. It is
supposed that citril finches are able to adapt
the nest building time to food availability. On
the north- and east-facing slopes finches are
known to feed mostly on nutritious pine
seeds (Borras et al., 2003), that are available
earlier. In contrast, birds at Bofia had to wait
until a sufficiently large supply of herb seeds
was available to rear their young (Borras et al.,
2003). Other factors for a later start of nest-
ing activity at Bofia may be found in the dif-
ference of elevation, and a higher portion of
Ardeola 53(1), 2006, 115-126
BREEDING PHENOLOGY AND NESTING HABITAT OF THE CITRIL FINCH 123
FIG. 7.—Age-determined pairs of citril finch Serinus citrinella (n= 33) at three slopes of Port del
Comte mountain (adult: 3rd calendar year or older; subadult: 2nd calendar year).
[Tipos de emparejamientos por el tipo de edad de los adultos reproductores de verderón serrano Serinus
citrinella (n= 33) en las tres laderas estudiadas en el Port del Comte.]
inexperienced subadult birds involved in breed-
ing at south-facing Bofia (see evidence for this
in Senar et al., 2002).
Pine trees were used exclusively for nesting
at the study sites. At south-facing Bofia, all
nests were built in mountain pines, whereas in
the lower areas of the two other study slopes
also scots pine was included in some cases.
This pattern reflects the natural limitation of
the two pine species at Port del Comte moun-
tain. Above 1900 meters, the mountain pine
is almost the only tree species, whereas in low-
er areas the slopes are dominated by scots pine.
However, it is obvious that the main popula-
tion of citril finches breeds in the mountain
pine at greater altitude instead of in the scots
pine zone. This obvious preference for moun-
tain pines also fits the close similarity in dis-
tributional pattern between this tree species
and citril finches in central Europe (Cramp and
Perrins, 1994; Glutz von Blotzheim and Bauer,
1997; Förschler, 2002a).
The highest proportion of second breeding
was observed at the south-facing slope (Bofia).
This was likely caused by the early loss of many
nests due to a late onset of spring during in-
cubation, with snow covering areas above 2000
meters for several days. Bad weather condi-
tions during the breeding period, such as in this
case, may be a reason for low breeding success
as well as higher predation rates due to higher
predator vulnerability. Additionally, due to the
lower habitat quality of Bofia, it is also sup-
posed that there is a larger portion of less fit
birds which inhabits these areas, which con-
firms such indications given by Senar et al.
(2002).
Nest height as well as vertical and hori-
zontal nest position were similar in all areas.
The observation of slightly higher nesting trees
in Vansa compared to the other two areas, may
be mainly explained by generally larger tree
heights on the north-facing slope. It is presumed
that birds in the other areas were limited to low-
er trees due to lesser availability of higher trees,
but there is a lack of more exact data on the
variation of vegetation height in the distinct ar-
eas to confirm this assumption. In general, two
types or even strategies of nest position choice
in pines may be distinguished. Nests were ei-
ther built close to the trunk in the tree crown,
or nests were located on outer parts of solid lat-
eral branches at lower parts of tall trees. Both
positions may be well suited to avoid predation
by abundant predators in the study area such
as jays Glandiarius garrulus (Förschler, 2002b)
and probably Formica ants (Förschler et al.,
2001).
Citril finches nested at Bof ia predominant-
ly in solitary trees, whereas at Port del Comte
more nests were found in tree groups, which
was caused by the more scattered habitat struc-
tures with single pines at Bofia. At Vansa, most
nests were built at forest edges and within pine
forest. These observations manifest themselves
also concerning the distance of nests to the
nearest closed forest, with birds of the north-
facing slopes nesting significantly nearer to
closed pine forest. This pattern reflects obvi-
ous habitat differences with more open land-
scape on south- and east-facing slopes and gen-
erally more wooded areas on north-facing
slopes (see indications for this in Senar et al.,
2002; Borras et al., 2003; Borras et al., 2004).
Human trails may be of special interest for
citril finches, because as edge habitats they of-
ten harbour particularly good food conditions
with larger diversity of distinct herbs and grass
seeds (Förschler and Kalko, 2006). In this study,
citril finches at Bof ia were nesting significant-
ly further away from human trails than did birds
in the other two areas. This might reduce the
quality status of south-facing Bofia versus the
other areas. Dandelion is one of the food plants
often associated to edges of tracks, which has
a special importance for citril finches as food
plant (Borras et al., 2003). However, it may
also be due to Bofia represents a more open
habitat, so human trails are not that important
as in a closed forest.
Furthermore, water plays an important role
for finches in general (Newton, 1972). Birds
FÖRSCHLER, M. I., BORRAS, A., KALKO, E., CABRERA, J., CABRERA, T. AND SENAR, J. C.
Ardeola 53(1), 2006, 115-126
124
of the east-facing slope had to fly greater dis-
tances to the nearest source with permanent
water. However, the quality of water resources
can be very different and birds at Bofia depend
only on a few water sites provided mainly by
human actvities. In contrast, birds at Vansa can
use the largest variety of fresh water sources.
Besides water, citril finches may be observed
frequently during the uptake of salt, presum-
ably for additional minerals (Borras et al.,
2003), a behaviour which is especially typi-
cal for conifer seed eating birds such as
crossbills Loxia curvirostra and siskins Car-
duelis spinus (Glutz von Blotzheim and Bauer,
1997). In all study areas, traditional salt places
were frequently used, and it is supposed that
birds sometimes have to fly over large distances
to get to these salt places (e.g. one morning in
five hours, nearly 100 individuals were caught
visiting the same salt place). In this study, birds
of Port Comte / Sucre had to undertake the
longest flight distance to reach such a salt place.
The distance to the nearest nest of another
citril finch pair was greatest at Bofia. The in-
creasing distance between the nests fits obser-
vations of different settlement structures and
population densities due to distinct habitat qual-
ity. Thus, in 2002 fewer breeding pairs and low-
er population densities were observed at Bofia
and higher population densities in the other
study areas. However, this observation may be
biased by the more scattered structure at Bofia,
so not only nests but also trees are at larger dis-
tances.
Finally, the highest proportion of 2nd cal-
endar year birds (subadults) involved in breed-
ing was also found at south-facing Bofia. It is
assumed that low quality areas such as Bofia
are mainly settled by low quality individuals
(subadult birds), which has been previously
supported by long-term ringing studies of the
species (Senar et al., 2002).
To summarise, several variations were found
in nesting habitat and phenology between the
three study sites. However, differences are small
and may be explained mainly by ecological
variation of living conditions in the distinct lo-
calities. Nonetheless these data are of interest
in the context of inter-local variation at Sierra
de Port del Comte, as indicated by other stud-
ies (Senar et al., 2002; Borras et al., 2003, 2004;
Förschler et al., 2005)
ACKNOWLEDGEMENTS.—This study was under-
taken in co-operation with the Max Planck Research
Centre of Ornithology Department Vogelwarte
Radolfzell (Prof. Dr. Peter Berthold). Gratitude is
also expressed to all other people involved in our
work, specially to Xevi Colomé and Jose Molina,
from Group Bages and Alex Casas. We also thank
Jordi García-Petit, director from the Parc Natural
Cadí-Moixeró and Reserva Nacional de Caça de
la Cerdanya-Alt Urgell (Departament de Medi Am-
bient, Generalitat de Catalunya) and the officers
from the Cos d’Agents Forestals and Guardería de
las Reservas, from Generalitat de Catalunya for fa-
cilities during the field work. We thank Andres Bar-
bosa, José A. Gil-Delgado and an anonymous ref-
eree for helpful comments on the manuscript. The
study was conducted with financial support from
the Max Planck Research Centre of Ornithology
and the University of Ulm (Landesgraduierten-
förderung Baden-Württemberg). This work is also
a contribution to project (BOS 2003-09589) from
the Spanish Research Council, Ministerio de Cien-
cia y Tecnología. It was furthermore supported by
a fellowship within the Postdoc-Programme of the
German Academic Exchange Service (DAAD).
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Marc I. Förschler is currently working on a Post-
doc-project about the demographic history of citril
finch sub-populations and has finished his PhD in
2004 on etho-ecology, biogeography and vocalisa-
tion of citril and corsican finches at the University
of Ulm and the Max Planck Research Centre for Or-
nithology, Vogelwarte Radolfzell. Antoni Borras
is graduated in Biology and cooperates with the Mu-
seum de Ciencies Naturals, Barcelona in studies on
metapopulations in citril finches. Elisabeth K. V.
Kalko is Professor and head of the Department of
Experimental Ecology, University of Ulm. Her main
research lines are studies on tropical diversity, com-
munity ecology and neuroethology in small mam-
mals. Josep Cabrera and Toni Cabrera are mem-
bers of the bird ringing group of the Institut Català
d’ Ornitologia, ICO. Juan C. Senar is head of Re-
search and Scientific Publication at the Museum de
Ciencies Naturals, Barcelona. His main research
lines are studies on ecoethology and evolutionary
ecology in Passeriformes.
[Recibido: 10-06-05]
[Aceptado: 05-03-06]
FÖRSCHLER, M. I., BORRAS, A., KALKO, E., CABRERA, J., CABRERA, T. AND SENAR, J. C.
Ardeola 53(1), 2006, 115-126
126
