Density, Habitat Selection and Breeding Success of an Insular Population of Barbary Falcon Falco Peregrinus Pelegrinoides

Abstract

We studied density, habitat selection and reproduction of Barbary Falcons Falco peregrinus pelegrinoides on Tenerife Island during 2004 and 2005. A total of 26 breeding pairs were counted, all of them occupying natural cliffs around the island. Density observed was 1.27 pairs/100 km2, and was positively correlated with cliff availability. Mean distance between neighbouring pairs was 5869 ± 3338 m, ranging from 1388–13 610 m; in some areas this value was as low as 2062 ± 673 m. Tenerife still shows potential for further increase regarding the observations of single females and the availability of potentially suitable but unoccupied cliffs. Falcons selected taller cliffs, more apart from roads and houses, near the coast, with lower presence of cultivated and urban areas, and associated with other cliff-nesting species. Stepwise discriminant analysis of habitat selection selected cliff height, nearest neighbour distance and distance to road, and correctly classified 71.1% of the cases. Productivity averaged 1.55 fledged young/pair and breeding success was 81.1%. No correlations were observed between habitat features and productivity. Since most territories are located in protected zones and human disturbance seems to be absent, special management measures are not necessary. However, further study into the biology of this population is required for effective and timely conservation of this species if need be.

Full text

INTRODUCTION
The breeding range of Barbary Falcon Falco pere-
grinus pelegrinoides generally comprises arid envi-
ronments from the Canary Islands and western
Morocco eastwards across scattered areas of North
Africa, the Middle East and some parts of central
Asia (Ferguson-Lees & Christie 2001). This raptor
is either considered a subspecies of the cosmopoli-
tan Peregrine Falcon F. peregrinus (Brosset 1986,
Del Hoyo et al. 1994, Wink & Seibold 1996) or an
independent species (Cramp & Simmons 1980,
Density, habitat selection and breeding success
of an insular population of Barbary Falcon
Falco peregrinus pelegrinoides
Rodríguez B., Siverio M., Rodríguez A. & Siverio F. 2007. Density, habi-
tat selection and breeding success of an insular population of Barbary
Falcon Falco peregrinus pelegrinoides. Ardea 95(2): 213–223.
We studied density, habitat selection and reproduction of Barbary Falcons
Falco peregrinus pelegrinoides on Tenerife Island during 2004 and 2005. A
total of 26 breeding pairs were counted, all of them occupying natural
cliffs around the island. Density observed was 1.27 pairs/100 km
2
, and
was positively correlated with cliff availability. Mean distance between
neighbouring pairs was 5869 ± 3338 m, ranging from 1388–13 610 m;
in some areas this value was as low as 2062 ± 673 m. Tenerife still
shows potential for further increase regarding the observations of single
females and the availability of potentially suitable but unoccupied cliffs.
Falcons selected taller cliffs, more apart from roads and houses, near the
coast, with lower presence of cultivated and urban areas, and associated
with other cliff-nesting species. Stepwise discriminant analysis of habitat
selection selected cliff height, nearest neighbour distance and distance
to road, and correctly classified 71.1% of the cases. Productivity aver-
aged 1.55 fledged young/pair and breeding success was 81.1%. No cor-
relations were observed between habitat features and productivity. Since
most territories are located in protected zones and human disturbance
seems to be absent, special management measures are not necessary.
However, further study into the biology of this population is required for
effective and timely conservation of this species if need be.
Key words: Falco peregrinus pelegrinoides, density, habitat selection,
reproduction, Tenerife, Canary Islands
1
La Malecita s/n, E-38480 Buenavista del Norte, Tenerife, Canary
Islands, Spain;
2
Los Barros 21, E-38410 Los Realejos, Tenerife, Canary
Islands, Spain;
3
Island Ecology and Evolution Research Group (IPNA,
CSIC), E-38206 La Laguna, Tenerife, Canary Islands, Spain;
4
Ctra. General 20 (San Vicente), E-38410 Los Realejos, Tenerife, Canary
Islands, Spain;
*corresponding author (benerguez@terra.es)
Beneharo Rodríguez1,*, Manuel Siverio2, Airam Rodríguez3& Felipe Siverio4

Clark & Shirihai 1995). It shows characteristic
plumage patterns and morphometric differences
with respect to Peregrine subspecies, but genetic
variation is quite low in the peregrinus/pelegri-
noides group (Wink et al. 2000). Although the
Canarian breeding falcons mainly show the
Barbary phenotype, haplotypes of both F. peregri-
nus brookei and F. p. pelegrinoides are present
according to a preliminary study carried out in
Fuerteventura (Amengual et al. 1996).
According to the last available estimate,
around 75 pairs breed in the Canary Islands,
where all islands are occupied (Siverio &
Concepción 2003). Until the end of the 1980s, its
presence and reproduction were only confirmed
for some localities on the eastern Canary Islands
(Hernández et al. 1991). Since then, its known
breeding distribution has expanded to the rest of
the islands (Delgado et al. 1999, Martín & Lorenzo
2001) and some aspects of its breeding biology
have been studied (Delgado et al. 1999). In
Tenerife its presence was mentioned in the past by
Meade-Waldo (1893) and Thanner (1909), but the
first breeding record was obtained as late as June
1991 (Hernández et al. 1992).
The density and breeding habitat of F. peregri-
nus have been studied extensively (Gainzarain et
al. 2000, Jenkins 2000a, Sergio et al. 2004,
Wightman & Fuller 2005). However, little is
known about the distribution pattern of Barbary
Falcon elsewhere, and no quantitative studies on
breeding habitat preferences exist, save for El
Hierro (Rodríguez & Siverio 2006).
The principal aims of the current study are: i)
to analyse distribution pattern and density of
breeding pairs of Barbary Falcon on Tenerife Island
in relation to breeding habitat selection, and ii) to
estimate breeding success and its relationship with
habitat characteristics.
MATERIAL AND METHODS
Study area
The Canary Islands are a volcanic archipelago,
which is located 100 km off the Atlantic coast of
north-west Africa (27°37'–29°25'N and 13°20'–
18°19'W), comprising seven major islands with
some small islets and rocks. The island of Tenerife
is the larger one (2034 km
2
and 3718 m a.s.l.),
and it is situated in the central part of the archipel-
ago. Vegetation and landscape are influenced by
north-easterly humid winds, altitude and orienta-
tion. Lower altitude coastal zones of the island are
covered by sparse and xeric vegetation dominated
by several succulent shrubs species (Fig. 1).
Different types of forest associated with local cli-
mate (thermophilous, laurel and pine woods)
appear at altitudes between 300 and 2000 m. In
the central higher altitude part of the island some
endemic shrub species dominate the landscape
(Morales & Pérez 2000, Fig. 1). Tenerife has
approximately 800 000 inhabitants, the majority
of which are concentrated along the coast
(Morales & Pérez 2000).
Field procedures
During the breeding seasons (February–May) of
2004 and 2005, suitable cliffs were inspected in
search of established pairs. The locations of some
pairs were already known before the current study
commenced (in this sense, some nest data pre-
sented in this work refer to the period 1992–
2005). Observation points and transects on foot
were used to pinpoint for each pair the breeding
cliff and nest site. The presence of an established
pair was assumed when displaying or perched
adults were present, and the nest site, recently
used perches on cliffs, territorial defensive behav-
iour and/or juveniles were also recorded.
Wherever possible, each occupied territory was
checked at least three times (prelaying, incubation
and chick-rearing periods) to determine the breed-
ing outcome.
Territories of Common Buzzard Buteo buteo,
Osprey Pandion haliaetus and Raven Corvus corax,
all three potential competitors for nest sites, were
noted during field observations, in addition to
data collected during previous investigations on
these species (Siverio 2006, authors unpubl.
data).
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ARDEA 95(2), 2007

Rodríguez et al.: BARBARY FALCON IN THE CANARY ISLANDS
215
Figure 1.
Different breeding habitats of Barbary Falcon on Tenerife Island: A) sea cliffs of Teno massif in the northwest
of the island, B) rock faces and lava fields above 2000 m altitude in the Teide National Park.

Data analysis
Territory dispersion was estimated by means of the
G-Statistic, the ratio between geometric and arith-
metic means of the squared nearest-neighbour dis-
tances (NND, Table 1). Values approaching 1
(>0.65) indicate a high degree of regularity, and
those close to 0 randomness (Brown 1975). Devia-
tion from randomness toward regularity of nest
spacing was evaluated by means of the test pro-
posed by Clark & Evans (1954).
To evaluate the effect of cliff availability, forest-
ed areas and human occupation on density, a
Spearman’s rank coefficient was calculated
between the number of pairs present in each 10-
km UTM (Universal Transverse Mercator) square
and the percentage of forest land, cliff availability
and dispersion of centres of human occupation.
These variables were obtained by dividing the 10-
km square into cells of 1x1 km (in the cases of
coastal areas, cells consisting of sea were not
216
ARDEA 95(2), 2007
Variable Description
Cliff characteristics
ALT Altitude in metres above sea level, from the top of the cliff.
ORI Orientation index, with higher scores for the sunniest and most sheltered orientations:
1, NE; 2, N & E; 3, NW & SE; 4, W & S; 5, SW.
HEIGHT Maximum height in metres of the cliff.
DOMINANCE Average difference of altitude – measured on the map – between the top of the cliff and the end of
three imaginary lines of 1 km that, from the cliff top, progress forward forming a right angle and
its bisection.
STEPNESS Difference in altitude between the highest and the lowest point within a 500 m circle around the cliff.
DISTCOAST Distance in metres to the nearest point of the coast.
DISTROAD Distance in metres to the nearest paved road.
DISTNPROAD Distance in metres to the nearest unpaved road.
DISTPATH Distance in metres to the nearest path.
DISTHOUSE Distance in metres to the nearest inhabited house.
NND Distance in metres to the nearest occupied falcon territory.
PRESBUTEOaPresence of Common Buzzard breeding pair.
PRESPANaPresence of Osprey breeding pair.
PRESCORaPresence of Raven breeding pair.
%FORESTaPercentage of land territory covered by trees.
%SHRUBaPercentage of land territory covered by shrubs.
%SEAaPercentage of territory covered by sea.
%OTHERSaPercentage of land with human uses (cultivations, houses, roads, etc.).
PROTAREA Location of territory inside a natural protected area.
CLIMBING Presence of climbing equipment in the crag.
Nest characteristics
NESTALT Nest altitude in metres above sea level.
NESTHEIGHT Height of nest in respect to the ground.
RELNESTPOS Relative height (%) nest/cliff, calculated as NESTHEIGHT/HEIGHT x100.
NESTORI Orientation index like ORI.
TYPE All nests were divided in three categories: edge, cavity or other.
a
Variable measured in a 9 km
2
circle around occupied and unoccupied sites.
Table 1.
Variables used in the description of habitat and nests of the Barbary Falcon on Tenerife Island.

considered), and noting the proportion of these
with cliffs, forest and human centres (see
Gainzarain et al. 2000 for similar procedure).
Twenty variables were used to describe nesting
cliffs and surrounding areas, and to quantify inter-
specific competition (Table 1). These variables
were measured in the field using GIS aerial pho-
tographs or 1: 25 000 scale maps. Only the most
recently used sites were considered in the statisti-
cal analysis. The same variables were measured in
twenty-six randomly chosen, apparently suitable
cliffs (≥50 m in height, vertical, dominant cliff
with crevices or ledges adequate for breeding),
unoccupied by falcons. To avoid the effect of
intraspecific competition, unoccupied crags had to
be more than 1 km away from the nearest estab-
lished falcon pairs (consistent with the approxi-
mate minimum distance recorded between occu-
pied nests in the same year).
Variables for occupied and unoccupied cliffs
were compared using t-test, Mann-Whitney U-test
or G-test (Table 2). For t-tests, some variables were
log-transformed to reduce the effects of non-nor-
mal distributions, as identified by Kolmogorov-
Smirnov tests. To understand habitat selection by
falcons, the same variables (excluding PRESBU-
TEO, PRESPAN, PRESCOR, PROTAREA and
CLIMBING; see Table 1) were employed in a step-
wise discriminant analysis (Fisher’s Linear Dis-
criminant Functions). A 5% level of significance
was specified for including variables in each step
of the analysis. To test the validity of the model
cross validation was employed.
Rodríguez et al.: BARBARY FALCON IN THE CANARY ISLANDS
217
Variable Occupied sites (n= 26) Unoccupied sites (n= 26) P-value
ALTb698.5 ± 588.8 853.0 ± 660.2 0.281
ORIc3.3 ± 1.4 3.0 ± 1.1 0.280
HEIGHTb230.0 ± 126.1 133.5 ± 66.4 0.001**
DOMINANCEc205.0 ± 154.3 201.0 ± 130.5 0.920
STEPNESSa441.2 ± 178.1 404.9 ± 144.1 0.423
DISTCOASTc3660.9 ± 4916.1 4252.4 ± 4766.2 0.164
DISTROADb1450.9 ± 1153.7 605.5 ± 700.7 0.007**
DISTNPROADb1065.1 ± 969.0 590.2 ± 553.2 0.033*
DISTPATHb320.6 ± 237.8 321.5 ± 307.4 0.749
DISTHOUSEb1879.4 ± 1568.7 1344.0 ± 1344.0 0.018*
NNDa5869.6 ± 3338.7 4821.6 ± 2171.9 0.186
%FORESTd15.4 ± 27.1 17.5 ± 23.6 0.512
%SHRUBd46.7 ± 26.3 41.5 ± 29.6 0.382
%SEAd24.8 ± 25.0 10.3 ± 15.6 0.015*
%OTHERSd13.1 ± 16.6 30.6 ± 30.1 0.034*
PRESBUTEOe65.4 61.5 0.773
PRESPANe15.4 0 0.015*
PRESCORe26.9 0 0.001**
PROTAREAe96.2 76.9 0.340
CLIMBINGe26.9 15.4 0.306
Table 2.
Mean values (± SD) of variables measured at territories of Barbary Falcon, and at unoccupied cliffs on Tenerife
Island.
Statistical results of univariate tests between the two samples (
a
t-test;
b
t-test carried out on the log transformed
variable;
cU-test; dt-test carried out on the variable arcsin transformed; e% of occupied and unoccupied sites with the
presence of other species, climbing equipment or inside a natural protected area, in this case, differences tested by
means of a G-test on the count data; significance level: * P< 0.05, ** P< 0.01).

To describe nest sites five variables were used
(Table 1). In addition to nests located during the
study period, all known nest sites used by falcons
during 1992–2005 in an intensively controlled
area (Teno massif, northwest of the island; M.
Siverio unpubl. data) were also considered.
Breeding success was calculated as the percent-
age of successful pairs (at least one fledged
young) from the total number of pairs checked
during the incubation period (n=16 in 2004, and
n=21 in 2005). Productivity and fledging rate
were calculated as the number of young fledged
per territorial and successful pair, respectively.
Potential differences in breeding success among
years were tested by means of the G-test or Mann-
Whitney U-test. Wherever possible fledged young
were sexed according to size differences (females
larger than males). Spearman’s coefficient correla-
tion analysis was employed to determinate the
effect of habitat variables on breeding perfor-
mance, first separately for each year, then pooled
for all breeding attempts, using mean values of
productivity for pairs that were observed in both
years.
Means and parameter estimates are reported
together with standard deviations. All statistical
calculations were carried out using SPSS (version
12.0) statistical package and statistical significance
was set at P< 0.05.
RESULTS
Density
A total of 26 breeding pairs of falcons, showing
field characteristics of Barbary, were recorded in
Tenerife occupying natural cliffs. Also, two single
females were recorded holding territories, and
pairs or single birds were observed in some unoc-
cupied sites that were potentially suitable for
breeding; these were omitted from the present
analysis. Total density on the entire island was
1.27 pairs/100 km
2
. Mean distance between
neighbouring pairs was 5869 ± 3338 m, ranging
from 1388–13 610 m. In some areas, such as Teno
massif (Fig. 1), this distance was as small as 2062
±673 m (n=7 pairs). The G-statistic value
(0.52) indicated a non-regular dispersion of breed-
ing territories. However the spacing pattern of ter-
ritories deviated from randomness toward regular-
ity (z= 3.19, P< 0.005).
Number of breeding pairs in each 10 km-
square ranged between 0 and 5. Only one variable
(cliff availability) of the three considered was sig-
nificantly correlated with falcon density (r
s
=
0.629, n= 34, P< 0.001; Fig. 2).
Habitat selection
Only large and natural cliffs, both in coastal and
inland areas, were used by falcons in Tenerife.
Mean altitude (measured on the top of the cliffs)
of falcon territories was 697.6 m (median 425 m;
range 75–2250 m). Only two pairs, located in the
Teide National Park, occupied crags at an altitude
in excess of 2000 m (Fig. 1).
Significant differences between occupied and
unoccupied crags were detected in eight variables
(Table 2). Falcons clearly selected taller cliffs, far-
ther apart from roads and houses, near the coast
and with a lower presence of human-transformed
areas. Furthermore, the presence of other cliff-
nesting species (such as Osprey and Raven) was
significantly different between occupied and unoc-
218
ARDEA 95(2), 2007
number of pairs
0
0
1
2
3
4
5
10 20 30 40 50 60 70
cliff availability (%)
Figure 2.
Relationship between the number of Barbary
Falcon pairs and cliff availability (expresed as percentage
of 1x1 km squares with presence of cliffs) in the UTM
squares of 10x10 km of Tenerife Island.

cupied sites by falcons. In addition, the falcons
tended to use only more sheltered orientations
(southwest-facing) for nests and cliffs (Fig. 3).
Four variables were selected for the discrimi-
nant analysis: LogHEIGHT, NND, LogDISTHOUSE
and
Arcsin%FOREST (Table 3). The percentage of
correctly classified cliffs was 75.0% (73.1% and
76.9% for occupied and unoccupied, respectively).
The robustness of the model was shown after
using cross validation as it correctly classified
approximately the same percentages of cliffs
(Table 3).
All nests were located opportunistically in
barren cavities (61.5%) or on ledges (34.6%),
except one which was located in an old Raven nest
(Table 4). No differences were found between
sheltered (orientation index values 4–5), neutral
(3) or exposed (1–2) nests to dominant winds in
Rodríguez et al.: BARBARY FALCON IN THE CANARY ISLANDS
219
A
B
C
0
1
2
3
4
5
6
S
N
NE
E
SE
W
NW
SW
0
1
2
3
4
5
6
S
N
NE
E
SE
W
NW
SW
0
1
2
3
4
5
6
S
N
NE
E
SE
W
NW
SW
Figure 3.
Slope aspect of cliffs and nest sites considered
in the present study (A = unoccupied cliffs, B = occupied
cliffs, C = nest sites).
Variables Occupied Unoccupied
Cliffs Cliffs
LogHEIGHT 52.966 47.418
NND 0.003 0.003
LogDISTHOUSE 22.547 19.278
Arcsin%FOREST –0.359 –0.293
Constant –103.242 –80.229
% correct classified 73.1 76.9
(n= 19) (n= 20)
% correct classified 65.4 76.9
cross validation (n= 17) (n= 20)
Table 3. Coefficients of the Fisher’s Linear Discriminant
Functions obtained for the occupied and unoccupied
cliffs by Barbary Falcons on Tenerife Island, and percent-
ages of correct cliff classifications according to the model
(n= number of cliffs).
Variables Minimum Maximum Mean ± SD
n= 26
NESTALT 65 2150 625.62 ± 556.24
NESTHEIGHT 30 387 142.42 ± 98.23
RELNESTPOS 23.29 79.86 53.41 ± 17.57
NESTORI - - 3.42 ± 1.24
Table 4. Physical characteristics of nests of Barbary
Falcon found on Tenerife Island during 1991–2005.

comparison with a random distribution (G
2
=
2.486, P=0.288). Maximum altitude and height
for all known nests were 2150 m and 387 m,
respectively. Nests were usually placed in the
upper half of the cliff, with a mean height of 142
m from the base of the cliff (Table 4). During the
period 1992–2005, seven intensively monitored
pairs in the northwest of the island used on aver-
age 2.86 alternative nests (range 1–5).
Breeding success
Breeding output was similar in 2004 and 2005
(Table 5), with a mean productivity of 1.55 and a
fledging rate of 1.76 over the two years combined.
Average breeding success was 81.1%, and no sig-
nificant differences were found between years in
breeding success (G= 0.784, P= 0.376) or fledg-
ing rate (U= 110.0, P= 0.438).
In 2004, negative relationships were detected
between fledging rate and three habitat variables
(n= 13): HEIGHT (r
s
= – 0.759, P< 0.05), STEP-
NESS (r
s
=– 0.639, P<0.05) and ORI (r
s
=
– 0.720, P<0.05). In the same year a positive
relationship was found between productivity and
% FOREST (r
s
=0.627, P<0.05). In contrast,
during 2005, or when data were pooled, no signif-
icant relations were detected between productivity
and the variables employed to describe habitat
features. A total of 28 fledged young were sexed
and no differences were found in sex ratio (14
males and 14 females).
DISCUSSION
Previous research on Barbary Falcon has mainly
been focused on field identification and taxonomic
status (Brosset 1986, Clark & Shirihai 1995, Wink
& Seibold 1996, Schollaert & Gilles 2000, Wink et
al. 2000, Corso 2001). In general, very little is
known about its biology worldwide (Dementiev
1957, Hogg 1983, Delgado et al. 1999, Brouwer &
Mullié 2000, Ming et al. 2003). Traditionally it has
been considered a desert form of the Peregrine
(Cramp & Simmons 1980, Ferguson-Lees &
Christie 2001).
In the Canary Islands this falcon was very rare
in past decades (Bannerman 1963), but a substan-
tial increase in population size has occurred in the
entire archipelago in the last 15 years (Delgado et
al. 1999, Siverio & Concepción 2003). On Tene-
rife, a 20% mean annual increase has been esti-
mated over the last 14 years (Hernández et al.
1991, present study). Most European Peregrine
populations are currently recovering from the col-
lapse induced by bioaccumulation of toxic organ-
ochlorines via prey species, and recently their
numbers appear secure again in the major part of
their distribution range (Ratcliffe 1997). Although
no precise data are available for the Canaries, cur-
rent legal status, hunting regulation on wild birds
and the high number of feral pigeons and doves
supposedly play an important role in the popula-
tion increase. The present density in Tenerife
appears to be similar to other healthy Peregrine
populations worldwide (Ratcliffe 1962, Olsen &
Olsen 1988, Pepler et al. 1991, Carlier 1993,
Ratcliffe 1993, Norris 1995, Gainzarain et al.
2000, Zuberogoitia et al. 2002), and to Barbary
Falcon populations elsewhere in the Canaries
(Rodríguez & Siverio 2006). The observations of
solitary females holding territories and the similar-
ity between occupied and unoccupied sites indi-
cate the potential for further increase.
Our results confirm that Barbary Falcons prefer
high cliffs in Tenerife, such as for example Teno
massif (Fig. 1), where also breed an important
Raven population and all Osprey pairs of the
island (Siverio 2006, authors unpubl. data).
220
ARDEA 95(2), 2007
2004 2005
Number of pairs 16 21
Breeding success (%) 87.5 76.2
Mean productivity 1.38 1.65
Mean brood size at fledging 1.64 2.20
Table 5. Breeding parameters of Barbary Falcon on
Tenerife Island during 2004–2005

However, in the eastern Canary Islands, where
large cliffs are scarcer than on western islands,
breeding pairs are also observed at small and
accessible hills situated in wide lava fields
(B. Rodríguez unpubl. data). In general, Peregrines
prefer large cliffs situated in areas with short vege-
tations and far away from human population cen-
tres; density and distribution are closely related to
cliff availability (Donázar et al. 1989, Jenkins
1994, Gainzarain et al. 2002). Heights of cliffs
used by Peregrines vary according to their avail-
ability, showing a preference for higher, more dom-
inant locations with respect to the surrounding
area (Pepler et al. 1991, Ratcliffe 1993, Gainzarain
et al. 2000). This fact is positively related with
breeding success and foraging efficiency (Mearns
& Newton 1988, Jenkins 2000b).
There is no simple explanation for the fact that
productivity in our study area was negatively
related to cliff height, sheltered orientations of cliff
faces and ruggedness of the nesting area; and posi-
tively related to percentage of forested land during
2004. However, it is likely that climatic stability,
geologic characteristics of cliffs (an abundance of
insulated potential nest sites) and the absence of
potential predators may explain some of these
findings. The positive correlation with forest cover
on the island may be spurious because of the small
surface area of forest anyway.
In cold-wet climates, Peregrines actively select
sheltered and sun exposed cliff-nest orientations,
and the opposite in warm climates (Olsen & Olsen
1989b, Norris 1995, Gainzarain et al. 2000, Jen-
kins 2000a), and this could be positively related to
breeding success (Mearns & Newton 1988, Olsen
& Olsen 1989a). In the Canaries, the structural
characteristics of cliff faces (an abundance of
crevices and ledges for potential nest sites), may
explain why only one falcon pair used an old
Raven nest. In other regions stick nests represent
around 30% of Peregrine nests (Ratcliffe 1993).
Whereas normally areas with a low density of
paved road are selected by falcons (Gil-Sánchez
1999, Gainzarain et al. 2000), transformed human
areas are also used by Peregrines and Barbary
Falcons as breeding, hunting or wintering sites,
and many man-made structures are utilized as
perching or nesting sites (Ratcliffe 1993, Brouwer
& Mullié 2000, Ferguson-Lees & Christie 2001). In
Tenerife, Barbary Falcon seem to avoid heavily
transformed human areas for breeding, but they
commonly hunt over towns and villages and occa-
sionally perch on electricity pylons.
Mean brood size at fledging observed on
Tenerife was in the lower range of values reported
for Peregrine in European populations; however,
breeding success was relatively high (review in
Rizzolli et al. 2005). The latter may be related to
the stability of a favourable climate and a pro-
longed breeding season of falcon’s prey species on
the island (Jenkins 1991, Jenkins & Hockey 2001,
Martín & Lorenzo 2001). Adverse weather with
snow during the breeding season only rarely
occurs at some high altitude nesting cliffs.
Never before – as far as we know – has the
density of Barbary Falcons been this high on
Tenerife, and some expansion is still possible. The
present conservation status seems to be satisfac-
tory, and we found no evidence of severe persecu-
tion or disturbance by humans. Falcons, however,
occasionally kill racing pigeons, and as pigeon fan-
cying is a popular sport on the island a conflict of
interest may arise in the future. General knowl-
edge on the ecology and biology of the Barbary
falcon is still incomplete, and further study into
diet composition, age structure of the population
and survival would improve its conservation sta-
tus, particularly in aiding early detection of nega-
tive population trends (Balbontín et al. 2003,
Pandolfi et al. 2004, Rizzolli et al. 2005).
Rodríguez et al.: BARBARY FALCON IN THE CANARY ISLANDS
221
ACKNOWLEDGEMENTS
This work was conducted without any financial support.
Special thanks to José Juan Hernández, Javier Martín,
Rubén Barone, Fernando Vizcaíno, Aurelio Acevedo,
David P. Padilla, Francisco J. Disque, Rut Martínez,
Francisco M. González and Tinguaro Montelongo for
their help in different ways. Statistical advice was given
by Joan Navarro and Juan Domingo Delgado. Alex
Brown improved the English version. Valuable comments
and corrections on the earlier draft of this manuscript
were given by José Antonio Sánchez-Zapata, Juan José
Negro and two anonymous referees.

222
ARDEA 95(2), 2007
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SAMENVATTING
Hoewel de meningen over de soortspecifieke status van
de Barbarijsche Slechtvalk onder taxonomen en cladisten
nog steeds uiteenlopen, wel of niet een soort, is de biolo-
gie van deze aan de Slechtvalk Falco peregrinus verwante
soort slecht bekend. Dat staat in schril contrast met de
Slechtvalk zelf, die overal ter wereld uitputtend is onder-
zocht. In deze studie worden dichtheid en habitatkeus op
Tenerife bekeken, het grootste van de Canarische eilan-
den op 100 km voor de kust van NW-Afrika. Deze vulka-
nische rotsklomp is ruim 2000 km
2
groot en herbergde in
de middenjaren 2000 – naast 800 000 mensen – 26 paren
en enkele ongepaarde territoriale vrouwtjes. De valken
nestelden op natuurlijke kliffen, met een gemiddelde
afstand tot het dichtstbijzijnde buurpaar van ruim 5800
m (lokaal, zoals in het Teno massief, echter slechts 2062
m). De valken hadden een voorkeur voor hoge kliffen
gericht naar het zuidwesten. Daarentegen werden gebie-
den met menselijke activiteiten juist gemeden als broed-
plaats, zij het dat ze in die gebieden wel jagend werden
waargenomen. De productiviteit lag met gemiddeld 1,55
jongen per paar aan de lage kant van de spreiding bij
Slechtvalken; daarentegen was maar liefst 81% van de
paren succesvol. Er werden geen duidelijke verbanden
gevonden tussen productiviteit en gemeten habitatvaria-
belen. Het stabiele klimaat, de aanwezigheid van talrijke
goed tegen de zon beschermde nestplekken op de ruige
kliffen en de afwezigheid van potentiële predatoren zul-
len daar mede debet aan zijn. Aangezien nog tal van der-
gelijke nestplekken onbezet zijn, of door een ongepaard
vrouwtje werden geclaimd, is er potentie voor verdere
uitbreiding. Conflicten met mensen zijn vooralsnog niet
aan de orde. Het vliegen met Postduiven Columba livia is
echter een populaire sport op Tenerife, en dat zou op ter-
mijn tot vervolging kunnen leiden als de valken vaker
postduiven gaan vangen. (RGB)
Corresponding editor: Rob G. Bijlsma
Received 12 November 2006; accepted 15 August 2007