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Density, habitat selection and breeding biology of Common Buzzards
Buteo buteo in an insular environment

Beneharo Rodríguez; Felipe Siverio; Airam Rodríguez a; Manuel Siverio; José J. Hernández; Jordi
Figuerola aaEstación Biológica de Doñana (CSIC), E-41092 Sevilla, Spain
First published on: 01 December 2009

To cite this Article Rodríguez, Beneharo, Siverio, Felipe, Rodríguez, Airam, Siverio, Manuel, Hernández, José J. andFiguerola, Jordi(2010) 'Density, habitat selection and breeding biology of Common Buzzards Buteo buteo in an insularenvironment', Bird Study, 57: 1, 75 — 83, First published on: 01 December 2009 (iFirst)
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Bird Study (2010) 57, 75–83

Density, habitat selection and breeding biology
of Common Buzzards Buteo buteo in an insularenvironment
BENEHARO RODRÍGUEZ1*, FELIPE SIVERIO2, AIRAM RODRÍGUEZ3, MANUEL SIVERIO4,JOSÉ J. HERNÁNDEZ5 and JORDI FIGUEROLA3
La Malecita s/n, E-38480 Buenavista del Norte, Tenerife, Canary Islands, Spain, 2Los Barros 21, E-38410
Los Realejos, Tenerife, Canary Islands, Spain, 3Estación Biológica de Doñana (CSIC), Avda. Américo
Vespucio s/n, E-41092 Sevilla, Spain, 4Constitución 19-3, E-38410 Los Realejos, Tenerife, Canary Islands,
Spain and 5La Habana 8–3°c (edf. Las Vistas), E-38650 Los Cristianos, Tenerife, Canary Islands, Spain

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Capsule Taller and sheltered cliffs located in rugged areas are selected for breeding and only some life
history traits fit the predictions of the so-called ‘insular’ syndrome.
Aims To analyse the density and nesting habitat preferences of Buzzards on the island of Tenerife, anddescribe the life history traits of this population.
Methods Density was studied by intensive field searching for all established pairs in a well-definedarea. Habitat features of breeding territories were compared with randomly selected sites using univariate
and multivariate analysis (GLM). Breeding biology was described based upon a total of 57 breedingattempts.
Results Density was positively correlated with estimated surface of forested areas. The best model
explaining characteristics of territory used for nesting reflected land ruggedness, nest shelter and distanceto the nearest Barbary Falcon breeding site. Mean clutch size was 2.60 ± 0.82, productivity was 1.68
± 0.97 and the percentage of successful pairs was 84.2%.
Conclusions Buzzards mainly use cliffs to nest, especially taller and sheltered ones, located in rugged
areas and in sympatry with Barbary Falcons. Characteristics of breeding territory did not predictproductivity. All reproductive rates were similar to those reported for some continental populations except
nesting success, which was higher.

Northern European populations of Common Buzzards
Buteo buteo are essentially migratory with wintering
areas in subtropical Africa, while southern and insular
populations tend to be sedentary (Ferguson-Lees &Christie 2001). This species’ biology has been wellstudied in Europe, where attention has focused on
density (Goszczyński 1997, Selås 2001, Sergio et al.
2002), habitat selection (Jędrzejewski et al. 1988,
Hubert 1993, Cerasoli & Penteriani 1996, Penteriani& Faivre 1997, Sergio et al. 2005) and reproduction(Tubbs & Tubbs 1985, Austin & Houston 1997, Krüger
2004). In these environments Buzzards are habitat
selective at the micro and landscape scales. Featuresthat allow secure positions for nests (high above
ground), near profitable foraging habitats (usually with*Correspondence author. Email: benerguez@terra.es© 2010 British Trust for Ornithology

low and highly diversified vegetation) and, at least
locally, remote from humans, are usually selected(Penteriani & Faivre 1997, Sánchez-Zapata & Calvo
1999, Zuberogoitia et al. 2004, Sergio et al. 2005).
The sedentary Buzzards of the Macaronesian archipelagos have been traditionally included in theendemic subspecies B. b. rotchschildi in the Azores,
B. b. harterti in Madeira, B. b. insularum in the
Canaries and B. b. bannermani in the Cape VerdeIslands, although the status of some of these taxons
is considered dubious (Ferguson-Lees & Christie
2001). Genetic and morphological studies suggestthat there are no differences between Canarian andMadeiran birds and the rest of the B. buteo buteo
group (Kruckenhauser et al. 2004). Despite theexpected differences in the life history traits of theseinsular populations compared with continental birds

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B. Rodríguez et al.

(the so-called ‘insular syndrome’ characterized bysmaller clutch sizes, later laying dates and higher
productivity and adult survival; see Williamson[1981]), data on density, diet, laying dates, clutch
sizes and breeding success of insular populations are
scarce (Bannerman & Bannerman 1965, 1966,
Naurois 1973, Martín & Lorenzo 2001, Palacios
2004). Furthermore, detailed information of thisnature is potentially of value in the conservationand management of raptor populations.
The Canarian populations of Buzzards have beenclassified as ‘near endangered’ (Barone & Atienza
2004). This raptor currently breeds on all the Canarianislands with the exception of Lanzarote, and occupies avariety of habitats. During the 1980s the breeding population was estimated at 430–445 pairs (Quilis et al.
1993). Although more recent quantitative data are notavailable, this population seems to be stable or slightly
increasing on some islands (Martín & Lorenzo 2001,
Palacios 2004, 2005), as occurs also in the majority of
its European breeding range (Bijlsma 1997).

The main aims of this study were to study density
and nesting habitat preferences of Buzzards on theisland of Tenerife, and to describe their life history
traits. We briefly discuss our findings in the context ofpreviously published results from continental
populations.
MATERIAL AND METHODS
Study area

The Canary Islands are a volcanic archipelago located100 km off the Atlantic coast of northwest Africa(27°37′–29°25′N and 13°20′–18°19′W). They consistof seven major islands and a number of small islets andoffshore rocky outcrops. The island of Tenerife, thelargest one of the group (2034 km2; highest point 3718
m asl), is situated in the central part of the archipelago(Fig. 1). Its vegetation and landscape are influenced byhumid north-easterly winds, altitude and orientation.
Lower altitude coastal zones are covered by sparse xeric

Figure 1. Location of Teno massif (study site for the density analysis) in northwest Tenerife.

© 2010 British Trust for Ornithology, Bird Study, 57, 75–83

Reproduction of insular Buzzards

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vegetation dominated by several succulent species ofshrub. Different types of forest associated with climatecharacteristics (thermophilous, laurel and pine woodland) appear at altitudes between 300 and 2000 m. In
the high central part of the island subalpine shrub
species dominate the landscape. The northwest of theisland is dominated by a well-conserved mountainous
area known as Teno (hereafter the Teno massif), which
covers some 140 km2 that greatly vary in altitude(0–1350 m asl; Fig. 1) with a great diversity of vegetation. It’s southwest coastline is characterized by a 12km-long chain of cliffs up to 500 m in height. The
majority of the massif’s surface area is protected by
Canarian environment legislation as Parque Rural andmany people living here still work in traditional agriculture and goat herding.
Data collection

During the breeding seasons (February–May) of 2006
and 2007 suitable sites were searched for establishedpairs of Buzzards. Adult birds were observed from a
distance in an attempt to find their nest sites. The
presence of an established pair was assumed when displaying or perched adults were present and when nest
sites, recently used perching sites, territorial defensive
behaviour, and/or juveniles were also observed. To
study the relationship between Buzzard nest density
and habitat characteristics, an intensive survey was
carried out in the northwest of the island in February
2007 (Teno massif, see Fig. 1). In this area, all occupied nest sites were mapped by observing adult behaviour (nest building, incubation, etc.). When it was
impossible to see a nest due to the terrain, the mostused cliff face or the central point where breeding
behaviour (calling, copulation, food or nest materialdelivered, etc.) took place was employed as the nesting site. Wherever possible, each occupied territory(both in Teno and the rest of the island) was checked
at least three times (pre-laying, incubation and chickrearing periods) to determine breeding outcome.
Clutch size was estimated on the basis of a sample ofnests (all of them located in cliffs) that could be
inspected from a higher position at a distance ofbetween 50 and 200 m using binoculars or a telescope.
Locations of Barbary Falcon Falco peregrinus pelegrinoides nesting sites were also noted during field work
and in previous studies of this species (Rodríguez et al.
2007), and they were taken into account during theanalysis. This species is a potential competitor of
Buzzards for nesting sites in Tenerife (pers. obs.), but it77

could also be positively influencing the distribution of
Buzzards, since kleptoparasitism on this species havebeen recorded (Siverio et al. 2008, pers. obs.).
Data analysis

The degree of regularity of nest site dispersion in Teno
massif was estimated as the G-Statistic: the ratio
between geometric and arithmetic means of the squared
nearest-neighbour distances (NND; see Table 1).
Values approaching 1 (> 0.65) indicate a high degreeof regularity in the spatial distribution of nests, while
those close to 0 indicate randomness (Brown 1975).
Deviation from randomness towards regularity in nest
spacing was evaluated by means of the test proposed by
Clark and Evans (1954).
To evaluate the effect of cliff availability, forested
areas and human occupation on the density of Buzzards
in the Teno massif, a Spearman’s rank correlation was
calculated between the number of pairs present in each
2.5-km Universal Transverse Mercator (UTM) squareand the percentage of cliffs (> 50 m high), forest andcentres of human occupation. These variables wereobtained by dividing the 2.5-km squares into 25 cells of
500 × 500 m (sea cells were not considered). The
proportions of cells with presence of cliffs, forest andbuildings from the total of 25 cells were assigned toeach 2.5-km square (see Gainzarain et al. [2000] forsimilar procedure).
Twenty variables were used to describe nesting
cliffs and surrounding areas that included distance toBarbary Falcon nesting sites (Table 1). To analyse
factors affecting the selection of nesting habitat, we
compared the variable values estimated for Buzzard
territories with those from 38 randomly selected
cliffs (n = 29) or trees (n = 9). To obtain random
locations, we generated random coordinates representing points on the map. All points situated in thesea or in non-potential breeding habitat (houses,
banana plantations, flat terrain without vegetation,etc.) were excluded from the analysis. We used ‘valid’
points to locate the nearest rock face or tree morethan 7 m high (i.e. 1 m + the minimum nest heightrecorded in this study) that we judged capable ofsupporting a hypothetical Buzzard nest (Sergio et al.
2005). Habitat variables were measured in the field(using an altimeter or scaled photographs), or
obtained from geographic information system aerial
photographs and 1:25 000 scale maps with 10-m
contour lines (Spanish National Institute ofGeography).
© 2010 British Trust for Ornithology, Bird Study, 57, 75–83

78

B. Rodríguez et al.

Table 1. Variables used in the description of breeding territories and nests of the Common Buzzard Buteo buteo on the island of Tenerife.
Variable
Territories
ALT
ORI

STEEPNESSNND
DISTFALCODISTCOAST
DISTROADDISTNPROAD
DISTPATH
DISTHOUSE%FORESTa%SHRUBa%OTHERSa%SEAa

Altitude in metres above sea level, from the top of the cliff or tree
Orientation index, with highest scores for the most sheltered orientations with respect to dominant winds: 1, NE; 2, N
and E; 3, NW and SE; 4, W and S; 5, SW
Maximum height in metres of the cliff or tree
Average difference of altitude – measured on the map – between the top of the cliff and the end point of three imaginarylines of 1 km that, from the cliff top or tree, progress forward forming a right angle and its bisection
Difference in altitude between the highest and the lowest point within a 500-m circle around the cliff
Distance in metres to the next nearest occupied Buzzard territory
Distance in metres to the nearest Barbary Falcon nesting site
Distance in metres to the nearest point of the coast
Distance in metres to the nearest paved road
Distance in metres to the nearest unpaved road
Distance in metres to the nearest path
Distance in metres to the nearest inhabited house
Percentage of land covered by trees
Percentage of land covered by shrubs
Percentage of land affected by human activity (agriculture, houses, roads, etc.)
Percentage of sea

Nests
NESTALTNESTHEIGHTRELNESTPOSNESTORI
TYPE

Nest altitude in metres above sea level
Height of nest above ground
Relative height (%) nest/cliff, calculated as NESTHEIGHT/HEIGHT × 100
Orientation index as for ORI
All nests were divided in three categories: ledge, cavity or tree

HEIGHT
DOMINANCE

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Description

Note: avariable measured in a 9-km2 circle.

We recorded the following breeding parameters: (a)clutch size; (b) fledging rate as the number of fledging
chicks/successful nests; (c) productivity as the numberof fledged young/territorial pairs; (d) hatchability as
the percentage of eggs that hatched out of the total;(e) breeding success as the percentage of laid eggs that
produced fledged young; and (f) nesting success as thepercentage of breeding attempts with at least one
fledged chick. Estimated laying dates per 10-day
period were back-calculated using chicks’ estimatedages and by considering 50–55 days and 34 days as
standard fledging and incubation periods, respectively(Cramp 1998). We estimated chicks’ ages by comparing their feather development with chicks from ninebroods correctly aged during this study. Potential
differences in breeding rates between the two years
were tested by means of the G-test and Mann–
Whitney U-test.
Principal component analysis (PCA) with varimax
rotation was used to reduce the number of independent variables from 15 to 4 factors (Eigenvalues > 1)
that retained 68.6% of the original variance (Table2). The first principal component (PC1) was clearlyinterpreted as a gradient of altitude. Given thathumans’ settlements are mainly located in coastal© 2010 British Trust for Ornithology, Bird Study, 57, 75–83

Table 2. Importance of habitat variables of Common Buzzard
Buteo buteo on the island of Tenerife with respect to each varimaxrotated factor of the principal components analysis (PCA). Factor
loadings values larger than 0.5 are indicated in bold.
Factor loadings

Variable
ALT
ORI
HEIGHT
DOMINANCESTEEPNESSDISTFALCODISTCOAST
DISTROADDISTNPROAD
DISTPATH
DISTHOUSE%FOREST%SHRUB%OTHERS%SEA
Eigenvalue
Explained
variance

PC1:
Altitudinal
gradient

PC2: Landruggedness

PC3:
Foraging
groundPC4:
Climatic
protection

0.855
0.080
−0.027
0.087
0.048
0.289
0.733
0.794
0.199
0.191
0.799
0.836
−0.066−0.721−0.5344.221
28.1−0.002−0.104
0.776
0.766
0.865
−0.404−0.331
0.205
0.286
0.138
0.003
0.038
−0.028−0.067
0.350
2.491
16.6

0.199
0.135
0.142
0.149
0.108
−0.1090.311−0.019
0.647
0.471
0.144
−0.3880.894−0.399−0.2732.064
13.8−0.2250.795
0.325−0.414−0.027−0.522−0.2640.187
0.136−0.0570.046−0.1170.144−0.116
0.318
1.511
10.1

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Reproduction of insular Buzzards

areas, and contrarily, forests, at high altitudes, ALT,DISTCOAST, DISTROAD, DISTHOUSE and%FOREST loaded positively, while %OTHERS and%SEA loaded negatively. PC2 was related to land ruggedness, with HEIGHT, DOMINANCE andSTEEPNESS variables loading positively. PC3 wasrelated to human-transformed areas currently abandoned and where shrubs grow abundantly;
DISTNPROAD and %SHRUB loaded positively.
Finally, PC4 reflected the shelter of territories (ORI
loaded positively), as well as the distance to the nearest Barbary Falcon nest site (DISTFALCO loaded
negatively; see Table 2).
We built glms using the four principal components
to explain breeding habitat characteristics (with binomial errors and a logit link function; logistic procedure in sas version 9.2) and to explore the relationshipbetween productivity (number of young fledged) andbreeding habitat features (with Poisson errors and a log
link function; genmod procedure). For those territories
with data from both study years, we randomly selected
one of the two, thereby ensuring data independence.
The aic was employed to select the best model (thelower the aic, and the lower number of variables, thebetter the model). Models with differences in aic < 2were considered as equally probable (Burnham &Anderson 2002).
RESULTS79

significantly correlated with Buzzard density (rs = 0.542,
P = 0.002, n = 30).
Habitat selection and nest-site characteristics

According to univariate analyses, Buzzards selecttall cliffs and rugged areas. Furthermore, distanceto the nearest Barbary Falcon breeding pair of occupied Buzzard territories is shorter than the randomsites (t-tests, P < 0.001, after sequential Bonferroni
correction; Table 3 ). Similar results were reachedthrough the logistic regression models. According
to aic weights, the best model explaining differences between breeding and not breeding territories
included land ruggedness (PC2) and climatic protection and distance to Barbary Falcons breedingpairs (PC4) (Table 4). Both principal components(PC2 and PC4) were statistically significant in themodel ( P = 0.0013 and 0.0074, respectively).
Studied nests were mainly located in the highest
parts of cliffs and oriented to medium scores of orientation index (see Table 5 for physical characteristicsof nests). NESTHEIGHT was positively related to
HEIGHT (r = 0.914, P < 0.001, n = 38). Except for
two located in trees (Pinus canariensis and Visnea
mocanera), all nests were located on cliffs (ledges
55.2% and cavities 42.1%). Of 22 breeding pairs
monitored during both breeding seasons, only eight(36.3%) used a different nest in the second year.

Density

Breeding biology

A total of 30 breeding pairs and one trio of adult Buzzards
were recorded occupying natural cliffs and trees in the
Teno massif during 2007. The total density in the area
was 23.13 pairs per 100 km2 (31 breeding territories).
However, if we consider only suitable breeding habitatfor Buzzards (i.e. excluding coastal plains with bushes,land covered by banana plantations and human settlements), the total density reached 27.51 pairs per 100
km2. The mean NND was 1081 ± 547 m (range 523–
2486 m, n = 31) in Teno and 2229.15 ± 1066.76 (range
1000–4478 m, n = 13) outside this massif. Statistical differences were found between NND in Teno and the restof Tenerife (U = 61.0, P < 0.001). The G-statistic value(0.65) indicated a degree of regular distribution of breeding territories in Teno that deviated significantly fromrandomness (z = 0.42, P < 0.001).
In Teno, the number of breeding pairs in each 2.5-km
square ranged between 0 and 4. Of the three variablesconsidered, only the percentage of forest land was

The first detected copulations and aerial displays took
place in late December, and most clutches (38.1%)
were laid in the first ten days of March (Fig. 2).
Clutch size ranged from one to five eggs, the majority
being of two (n = 11, 44%) and three (n = 11) eggs,
and only single clutches of one, four or five eggs weredetected. No significant relationships were foundbetween clutch size or productivity and the timing oflaying, and no significant differences were detected
between years in any of the breeding parameters analyzed (Table 6).
The most parsimonious models analysing the effectof habitat features on number of young fledged (productivity) did not obtain the lowest aic values. They
included the PC1 and PC3, and PC3 and PC4
respectively (Table 4). However, neither of principal
components was present in all competing models
and they were not statistically significant at any
competing models (P < 0.29); suggesting that the© 2010 British Trust for Ornithology, Bird Study, 57, 75–83

80

B. Rodríguez et al.

Table 3. Mean values ± sd of variables used in the description of breeding territories of the Common Buzzard Buteo buteo on the island of
Tenerife. Statistical results of univariate t-tests between the two samples.
Occupied territories

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Variable
ALTb
ORIe
HEIGHTc
DOMINANCEaSTEEPNESSa
DISTFALCOc
DISTCOASTc
DISTROADb
DISTNPROADb
DISTPATHb
DISTHOUSEb%FORESTd%SHRUBd%OTHERSd%SEAd

Random sites

Mean ± sd (n)RangeMean ± sd (n)

Range

P

648.6 ± 313.3 (35)3.3 ± 1.2 (34)106.7 ± 64.7 (35)145.0 ± 166.8 (35)411.0 ± 125.8 (34)2320.4 ± 1684.5 (38)3263.8 ± 2690.7 (38)559.2 ± 628.4 (38)294.7 ± 203.8 (38)221.0 ± 177.1 (38)701.9 ± 592.8 (38)17.7 ± 19.9 (38)53.4 ± 25.9 (38)23.7 ± 20.8 (38)5.2 ± 10.0 (38)

170–1492
1–5
10–268−172–480
190–630
100–6045
215–11 367
62–3430
33–934
5–692
110–2930
0–93.03.09–94.4
0–77.90–33.7863.0 ± 674.4 (38)2.5 ± 1.3 (38)46.7 ± 35.5 (38)113.3 ± 113.0 (38)275.7 ± 134.9 (38)4300.7 ± 2454.9 (38)5275.1 ± 4121.2 (38)794.7 ± 802.0 (38)316.2 ± 332.9 (38)187.0 ± 234.1 (38)1627.7 ± 1802.4 (38)25.5 ± 31.1 (38)45.6 ± 29.4 (38)25.4 ± 26.5 (38)3.5 ± 10.3 (38)75–2670
1–5
7–150−75–487
110–685
10–10 780
7–18 450
35–3788
15–1765
5–110070–6550
0–100.0
0–98.50–85.8
0–40.50.730
0.010< 0.000*
0.343< 0.000*
0.001*
0.025
0.355
0.661
0.182
0.067
0.508
0.183
0.947
0.258

Note: at-test carried out on untransformed variables; bt-test carried out on the log-transformed variable; ct-test carried out on the square-roottransformed variable; dt-test carried out on the arcsin-transformed variable; et-test carried out on the ranked variable; *significant using thesequential Bonferroni correction.

Table 4. Competing GLMs explaining territory occupation (withbinomial errors and a logit link function) and productivity (withPoisson errors and a log link function) of Common Buzzard Buteo
buteo in Tenerife (Canary Islands). For each model, the AIC, thedifference between the current model and the best model (∆ AIC),
and the Akaike weights (w) are given. Variables retained in allcompeting models are in bold.
Model/variables
Occupation models
PC2 + PC4
PC1 + PC2 + PC4
PC2 + PC3 + PC4
PC1 + PC2 + PC3 + PC4
Null model
Productivity models
PC1 + PC3 + PC4
PC1 + PC2 + PC4
PC1 + PC3
PC3 + PC4
PC1 + PC2 + PC3 + PC4
Null model

AIC

∆ AIC

w

91.19
91.77
92.29
92.85
107.36

0.00
0.58
1.10
1.65
16.17

0.36
0.27
0.21
0.16
−

165.01
166.13166.18166.24166.53169.76

0.00
1.12
1.17
1.23
1.52
4.75

0.32
0.18
0.18
0.17
0.15
−

Table 5. Physical characteristics of Common Buzzard Buteo buteo
nests observed on the island of Tenerife during the present study(n = 38).

NESTALTNESTHEIGHTRELNESTPOSNESTORI

Minimum

Maximum

Mean ± sd

113
6
18.57
–

1485
175
90.0
–

590.32 ± 310.40
67.82 ± 49.97
59.59 ± 19.26
3.13 ± 1.07

© 2010 British Trust for Ornithology, Bird Study, 57, 75–83

analysed habitat features did not significantly influence productivity.
DISCUSSION

The average density estimated as pairs per 100 km2(23.13) or mean NND (1081 ± 547) of Buzzards in the
Teno massif is similar to that of continental populations (see Sergio et al. [2002] for a review). Density inTenerife is positively related to forest distribution, as
occurs also in some populations in Central andSouthern Europe (Goszczyński 1997, Sánchez-Zapata& Calvo 1999, Sergio et al. 2005). This pattern may berelated to the typical situation of human settlements
and cultivation in flat areas in the island, with forests
left to occupy the abrupt rocky areas where Buzzards
usually establish their nests. Habitat expansion is a regular feature of island bird populations (Williamson
1981, Thibault et al. 1992). Contrary to continental
populations, where Buzzards almost always breed inforest patches, or in areas with some degree of tree
cover (Ferguson-Lees & Christie 2001), in the CanaryIslands this species occupies a wide range of habitats
for nesting from sea level up to 1500 m asl, including
sparse scrubland without trees (e.g., in the island of
Fuerteventura) and deeply forested areas (Martín &Lorenzo 2001, present study).
Cliff nests, generally less accessible than tree nests
and often distant from human population centres andDownloaded By: [Rodríguez, Beneharo] At: 16:26 4 February 2010

Reproduction of insular Buzzards

81

Figure 2. Distribution of estimated laying dates (n = 42) in Common Buzzards Buteo buteo during the 2006 (dark grey) and 2007 breeding
seasons on the island of Tenerife.
Table 6. Reproductive parameters of Common Buzzards Buteo buteo during 2006–2007 on the island of Tenerife. Data are presented asmeans ± sd (n).
Parameters
Mean clutch size
Fledging rate
Productivity
Hatchability
Breeding success
Nesting success

2006

2007

Total

2.36 ± 0.63 (14)2.10 ± 0.55 (20)
1.68 ± 0.99 (25)
81.82 (33)76.67 (30)80.0 (25)

2.91 ± 0.94 (11)1.93 ± 0.78 (27)1.68 ± 0.98 (31)82.76 (29)65.63 (32)87.5 (32)2.60 ± 0.82 (25)2.00 ± 0.69 (47)
1.68 ± 0.97 (56)78.46 (62)70.97 (62)84.21 (57)roads, are probably preferred by Buzzards where they
are available (Thibault et al. 1992, Sergio et al. 2002,
present study). Buzzards could select steep slopes thatmaybe favour their soaring flight (Selås 1997, andreferences therein). Our results indicate that Buzzards
select nesting sites with high gradient slopes which may
be related to their soaring activities, lack of human disturbance and/or to the fact that this type of terrain has
a greater variety of microhabitats. Another importantfactor in assessing the quality of nesting sites in raptors
is protection from inclement weather (Newton 1979).
In Tenerife Buzzards may be selecting sheltered orientations (driest and sunniest) for nesting according to

univariate test comparing the orientation index ofoccupied and non-occupied territories (P = 0.01, but
not significant after applying sequential Bonferroni
correction). Furthermore, PC4, which is highly andpositively related to territory orientation index, wasincluded in all competing logistic regression models(Table 4).
In some continental areas, competition between
Buzzards and other raptor species for breeding sites or
hunting habitat has been reported (Kostrzewa 1991,
1996, Krüger 2004, Sergio et al. 2005). Experimental
evidence suggests that the presence of Northern
Goshawks Accipiter gentilis could reduce productivity in© 2010 British Trust for Ornithology, Bird Study, 57, 75–83

Downloaded By: [Rodríguez, Beneharo] At: 16:26 4 February 201082

B. Rodríguez et al.

Buzzards (Krüger 2002). In Tenerife, Barbary Falcons
and Common Buzzards have similar insular distribution
patterns, although Buzzards are absent from highest
altitudes of El Teide National Park (Lorenzo 2007,
Rodríguez et al. 2007), and both species have successfully occupied nest-sites less than 200 m apart (pers.
obs.). Results of the univariate tests in our study showedthat Buzzard nesting sites are significantly closer toBarbary Falcon nests than random sites. Further studies
are required to evaluate causes of this apparent relationship between these two species, since some cases ofkleptoparasitism by Buzzards on this falcon have been
observed recently in Tenerife (Siverio et al. 2008, pers.
obs.).
In several European populations annual breeding
density and productivity are greatly influenced by foodresource availability and variations in the weather(Spidsø & Selås 1988, Kostrzewa & Kostrzewa 1990,
Graham et al. 1995, Goszczyński 1997, Selås 2001,Lõhmus 2003). Due to the climatic stability of most of
the Canary Islands (Marzol-Jaén 2000) and its expected
low annual variation in the population size of its main
prey species (rabbits, rats and lizards; pers. obs.), it islikely that no large variations in breeding density or
breeding rates occur between years.
Breeding parameters such as clutch size and fledging
rate in our population are similar (within the range) if
compared to continental populations (see review in
Sergio et al. [2002]). However productivity and nesting
success estimated in Tenerife are higher than thosereported for some European populations (Sergio et al.
2002). Climatic stability (Marzol-Jaén 2000) could be
responsible for the fact that the majority of pairs raised
at least one chick until fledging. In a community study
analysing ‘insular’ characteristics of Corsican raptors(Mediterranean), some species (including the Common
Buzzard) apparently did not show different breeding
traits with respect to the nearest continental populations suggesting that other factors such as, for example,
diet diversity could be also regulating breeding traits(Thibault et al. 1992).
Although nesting sites of Buzzards in Tenerife seem tobe secure against humans, foraging grounds are usuallysituated in flat terrain so they are vulnerable to urban
development. This fact, together with the other threat
factors reported for this population, such as shooting,collisions and poisoning (Lorenzo 2007, pers. obs.), suggest that detailed studies focusing on population dynamics, particular aspects of reproduction, habitat use andcauses of adult mortality will be useful tools for detecting
population trends at devising management strategies.
© 2010 British Trust for Ornithology, Bird Study, 57, 75–83

ACKNOWLEDGEMENTS
Although this work was conducted without financial support, we are very grateful to the Town Council of Villa
Histórica de Santiago del Teide for help with some field
expenses. Special thanks are also due to Rut Martínez, Nazaret Carrasco, Juan Curbelo and Abraham Hernández for their
help with the field work. Luis Cadahía, Florentino De Lope,
Juan J. Soler, Phil Whitfield, Rob G. Bijlsma and Graham
Martin made valuable comments and corrections on an earlier draft of this manuscript and improved the English
version.

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(MS received 27 May 2009; revised MS accepted 4 September 2009)© 2010 British Trust for Ornithology, Bird Study, 57, 75–83