Analysis of reservoir selection by wintering ospreys (Pandion haliaetus haliaetus) in Andalusia, Spain: A potential tool for reintroduction

2005·2.3 MB·English

by  E Casado

168 Short Communications VoL. 39, No. 2
las Montanas Rocosas en las decadas de 1960 y 1970. En Cade, Brian Millsap, and an anonymous reviewer helped
el ano 2004 revise 15 de los 21 acantilados utilizados por importantly with revision of the original manuscript.
Falco peregrinus en el pasado en Colorado para determi- Literature Cited
nar los cambios en la ocupacion y en las tasas de produc- Craig, G.R. andJ.H. Enderson. 2004. Peregrine Falcon
tividad. En el ano 2004, la tasa de ocupacion por pareja
biology and management in Colorado 1973-2001
fue de un 87% en comparacion con un 47% un 40%
y Tech. Publ. No. 43. Colorado Division ofWildlife, Fort
entre 1963-65 y 1973-75, respectivamente. La tasa re- CO
Collins, U.S.A.
productiva basada en todas las parejas con territorios fue Enderson, J.H. 1965. A breeding and migration survey
de 2.1 juveniles/pareja, en comparacion con una tasa de
of the Peregrine Falcon. Wilson Bull. 77:327-339.
1.2 y 0.7 para los periodos anteriores, respectivamente.
ANDJ. Craig. 1974. Status ofthe Peregrine Falcon
Se estima que 136 parejas nidifican en unos 160 acanti-
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lados donde F. peregrinus estuvo presente en la ultima de- , AND W.A. Burnham. 1988. Status ofper-
cada, pero el numero real es seguramente mayor y pod- egrines in t,he Rocky Mountains and Colorado Pla-
ria aumentar a 250-400 parejas dada la estimacion de la teau. Pages 83-86 in T.J. Cade, J.H. Enderson, C.G
disponibilidad de habitat apropiado. Thelander, and C.M. White [Eds.], Peregrine Falcon
[Traduccion del equipo editorial] populations: their management and recovery. The
Peregrine Fund Inc., Boise, ID U.S.A.
Acknowledgments
Hickey, (Ed.). 1969. Peregrine Falcon populations:
J.J.
Colorado College and the Colorado Division ofWild- their biology and decline. Univ. Wisconsin Press, Mad-
life funded travel in 2004. Myron Chase andJason Ferrell ison, WI U.S.A.
of the National Park Service, and Brent Bibles, graciously
provided occupancy information from eight sites. Tom Received 10 September 2004; accepted 28 March 2005
/. RaptorRes. 39(2):168-173
© 2005 The Raptor Research Foundation, Inc.
Analysis of Reservoir Selection by Wintering Ospre\s {Pandionhaliaetus haliaetus) in
Andalusia, Spain: A Potential Tool for Reintroduction
Eva Casado^ and Miguel Ferrer
Department ofBiodiversity Conservation, Estacion Biologica de Donana, CSIC, Pabellon del Peru,
Avda. Maria Luisa s/n, 41013 Sevilla, Spain
KeyWords: Osprey, Pandion haliaetus; reintroduction',pre- 1992). However, Ospreys still winter in some parts of
dictive model', reservoirs:, southern Spain', fish production. Spain. Historically, Andalusia was an important breeding
area for this species in Spain, and currently is an impor-
The extant Mediterranean Osprey {Pandion haliaetus tant wintering and stopover area for migrant birds (Os-
haliaetus) breeding population is largely fragmented in terloff 1977, Saurola 1994).
Morocco, Corsica, and on a few islands from the Balearic Reservoirs are occupied extensively by breeding Os-
and Canary archipelagos, which support isolated-rem- preys in most of their range, but they are a relatively new
nant populations (Gonzalez et al. 1992, Thibault et al. ecosystem in Spain. Reservoirs of 150 ha or more covered
1996). The disappearance ofthe Osprey as breeding bird 25 500 ha (0.3% ofAndalusia) during the 1960s, butnow
in the coastal region of mainland Spain was due to the (MOPU
cover twice this area 1991). Construction of ar-
loss of suitable nesting sites resulting from the develop- tificial impoundments may have enhanced the spread of
ment of a tourist infrastructure (Gonzalez et al. 1992) Osprey populations in other areas due to habitatcreation
and human persecution (especially by theft of eggs or
(Van Daele and Van Daele 1982, Houghton and Rymon
chicks) Ospreys have been extinct as a breeding species
. 1997). Reservoirs often provide foraging advantages over
in continental Spain since the 1980s (Gonzalez et al.
rivers and lakes because they are shallow and open-water
areas, vfith reduced turbidity that improve the detectibil-
1 Email address: [email protected] ity ofprey (Vana-Miller 1987 and references therein). An
. ..
June 2005 Short Communications 169
Osprey reintroduction project involving recently-created Surveying all ofAndalusian reservoirs was not possible
reservoirs was initiated in Andalusia in 2003 to re-estab- due to the limited time of the study period (4 mo m
lish a breeding population on the Iberian Peninsula (Ca- winter). Thus, we had to reduce the sample size to 20
reservoirs which were selected on the basis of previously
sado and Ferrer 2004).
reported sight records of Osprey. First, 10 reservoirs with
Requirements of wintering Osprey involve primarily
previous historical records of wintering Ospreys were
abundance of food supplies (Newton 1979, Prevost
chosen. Then, for comparison, we randomly selected 10
1982), but physical structure of habitat may also affect
reservoirs without previous records ofwintering Ospreys.
accessibility to prey (Moore et, al. 1993 and references Habitat Measurements. We collected data on 17 vari-
therein). Fish production or standing crop depends on ables possibly affecting both abundance and availability
reservoir features such as mean depth, surface area, of fish to Ospreys (Table 1). We assumed that shorelines
shoreline development, water level fluctuation, age, and of reservoirs were more likely to be affected by human
storage ratio, factors that also affect availability ofprey to activity than reservoir centers. Thus, distances from res-
Osprey (Jenkins 1970, 1976, Sancho Royo and Granados ervoir shoreline to the nearest distribution and transmis-
1988). Also, the quality of a reservoir for a wintering Os- sion power line, nearest paved road, and nearest urban
prey may be affected by human activity or by the avail- center were measured to provide estimators of human
ability ofhunting and resting perches. We surveyed struc- activity.
tural characteristics, human disturbance, and availability Other habitat features included in analyses were dis-
tance from a reservoir to nearest reservoir >150 ha, dis-
of perches on reservoirs to determine factors affecting tance to nearest coast, and number of arms (thin prolon-
occupation by Osprey. gation of water) of over 100 m length X reservoir
surface^^ (“number of arms”). Reservoirs on flat terrain
StudyArea
usually have few arms, but more large tails than those
Andalusia is the southernmost Spanish autonomous re- situated in mountain valleys. Number of reservoir arms
gion, with 64 man-made freshwater impoundments >150 was an index of surrounding topographical relief (i.e.,
ha in size, covering a total of50 183 ha and have a storing higher index values indicated more relief)
capacity of 9403 hm^ of water. Reservoirs studied were Distances, number of arras, and shoreline length were
situated among mountains near the seacoast (Betic measured on 1:50000 topographic maps prepared by the
Chain) and in valleys of the Guadalquivir River and its Spanish Army Cartographic Service, using a ruler and a
tributaries. Climate ofAndalusia is mild, with maximum digital curvimeter, respectively.
and minimum temperatures in winter 20.7°C and —2°C, Percent of tree cover within a 20-m wide band around
respectively (Instituto Nacionalde Meterologia 2004)
the reservoir edge was considered to be an index of
Barbel {Barbus spp.), Iberian Nose {Chondrostoma spp.), perch availability and was obtained from land-use maps
and Carp {Cyprinus carpio) are the primary prey species of the Spanish Ministry of Agriculture, using SYGMAS-
of Osprey in Spanish reservoirs (Sancho Royo and Gra- CAN pro 4.0 image analysis software (Fox and Ulrich
nados 1988, Gil Sanchez 1995, Lekuona 1998). Predom-
1995).
inant vegetation was crop fields in valleys, and pines {Pi-
Water-exchange rate (the percentage of the difference
nus spp.) and cork oak {Quercus suber) scrub in the
between the water entry and the water exit, in relation
mountains. Eucalyptus {Eucalyptussp.) have been planted
around reservoirs with recreational facilities. to the mean volume of the reservoir; Table 1) between
March 1997 and March 1998 was calculated from data
Methods coming from Guadalquivir and south hydrographic con-
federacies (Spanish Environment Ministry)
Selection of Reservoirs and Survey of Wintering Os-
Data Analyses. Statistical analyses were conducted us-
prey. Historical data about presence ofwintering Osprey ing STATISTICA (1986). Variables were transformed
from published sources and from official state reports, (square-root and log [1 + square root]) when necessary
from banding centers, wildlife-recuperation centers, and to achieve a normal distribution. When variables could
unpublished observations of naturalists and researchers
not be normalized, nonparametric statistics were used for
were used to identify occupied reservoirs in our study
comparisons. Correlation among variables was evaluated
area. Records of Osprey sightings in the study area be-
by a factor analysis and covariates were removed. The
tween November and mid-March over the winters of
remainingvariables were included in a discriminantfunc-
1984-85 to winter 1996-97 were collected.
Systematic surveys on reservoirs were conducted in the tion analysis, which was employed to determine the res-
winter of 1997-98 (mid-November-mid-March) to inves- ervoir features that were associated with Osprey pres-
tigate the occupancy of each reservoir by Ospreys. Two ence. Variables for the discriminant analysis were
45-min Osprey searches were conducted with binoculars introduced three at a time due to the small sample size.
(8 X 30) and spotting scope (20 X 60) from different One variable from each ofthe three factors obtained was
observation points at each reservoir. Searches were con- included in every entry group in order to avoid co-rela-
ducted by the same observer between 0800—2000 H (so- tions; thus several combinations of variables were ana-
lar time) Reservoir searches were conducted with similar lyzed with the discriminant function approach. The for-
.
weather conditions, avoiding those days with precipita- ward stepwise method was used and significance was set
tion or high winds, both in the morning and in the even- at P < 0.05.
ing. One observation point was always at the head of the As a measure of the model’s ability to predict Osprey
dam, and the other at the opposite end of the reservoir. occupation of reservoirs, validation was carried out using
170 Short Communications VoL. 39, No. 2
Table 1. Comparison of habitat variables between occupied and unoccupied surveyed reservoirs.
Occupied Unoccupied
N Mean N Mean pa
Meters above sea level 7 10.53 13 11.79 0.362
Years since reservoir construction to winter 1997-98 7 30.29 13 33.85 0.662
Mean surface area (ha) 7 1476.53 13 471.86 0.166
Mean water depth (m) 7 18.14 12 13.31 0.397
Distance from reservoir shoreline to nearest >150 ha
reservoir (km) 7 88.31 13 98.94 0.403
Distance from reservoir shoreline to nearest paved road
(m) 7 35.71 13 42.31 0.591
Distance from reservoir shoreline to nearest urban center
(km) 7 35.30 13 56.39 0.048
Distance from reservoir shoreline to nearest distribution
power line (m) 7 24.71 13 5.27 0.172
Distance from reservoir shoreline to nearest coast (km) 7 169.30 13 228.92 0.143
Number of arms longer than 100 m in length/reservoir
surface (ha) 7 0.16 13 0.23 0.030
Shoreline (km) 7 55.41 13 33.86 0.285
—
Water exchanged, which was calculated by: (entry hm^
exit hm^) X 100/(mean volume hm^) 7 0.084 13 0.024 0.063
Shoreline development. Ratio of the shoreline length to
the circumference of a circle with an area equal to that
of the reservoir. Calculated through the function L/2 X
V(n X A) being L = shoreline length in km, A =
,
area of reservoir (ha) 7 0.40 13 0.43 0.781
Depth where a Secchi disk of 20 X 20 cm was not visible 7 68.44 13 78.35 0.968
Distance from reservoir shoreline to nearest pole of trans-
mission power line (m) 7 27.01 13 34.27 0.838
Percent of shoreline length occupied for dense canopy 7 3.06 8 1.92 0.270
Trophic state = 10 (6-logD); D = Secchi disk depth 7 -1.96 13 2.35 0.405
Probability that occupied and unoccupied distributions were different was obtained by the Mann-Whitney Ctest. Probabilityvalues
in bold indicate statistical significance.
42 more Andalusian reservoirs with previous records of opment, water transparency, distances from reservoir
occupation by Osprey. shoreline to the nearest distribution and transmission
power line, to the nearest paved road, to the nearest ur-
Results
ban center, to the nearest reservoir, to the nearest coastal
Twenty reservoirs covering 16 482 ha were included in point, square root of number of arms, and percent of
the analyses (Table 2); these represented 31.25% of res- tree cover were the non-related variables that were con-
ervoirs by number and 33% by surface in Andalusia. Ac- sidered for further analysis. Shoreline length (km) mean
,
cording to major operational function, one reservoir was surface area (ha), concentration ofdissolved organic ma-
classified as a hydropower reservoir, six as irrigation, nine terial in water (trophic state), and water depth (m) were
as municipal water supply, three as recreational use, and redundant and thus, not included in further analysis. Fac-
one for mining use (MOPU 1991). tor analysis provided three principal factors. First, one
Observations of wintering Ospreys in Spain increased contributed to 23.77% of total variance and showed the
from 15 individuals in winter 1984—85 to 47 in winter highest factor loading with distance to nearest distribu-
1996-97. Of 522 sightings of wintering Osprey in Spain, tion power line, to nearest reservoir, forest cover, and the
400 were from Andalusia. Every Andalusian estuary and transformed index of number of arms and altitude. The
marsh was occupied by wintering Ospreys, and 19 out of second factor explained 18.82% oftotal variance and was
64 Andalusian reservoirs were occupied. Seven of the 20 related to water transparency, distance to nearest urban
sampled reservoirs were occupied by Osprey. center, and log transformed water-exchange rates. The
Altitude (square-root transformed) of reservoirs, age, third factor, which explains 15.81% oftotal variance, and
water-exchange rates (log transformed), shoreline devel- loaded with age of reservoir, shoreline development.
June 2005 Short Communications 171
Table 2. Probability of occupation and presence of Os- flected by this variable, seemed to be avoided by Osprey
prey on surveyed reservoirs in Andalusia, Spain. Reservoirs with a circular shape are shallower and have
higher exchange between the entry and exit of water
These factors are associated with higher productivity
Occupation
(Jenkins 1976, Ryder 1982), providing a better food sup-
Reservoirs Osprey Presence Probability
ply to fish-eating birds than those reservoirs located with-
Agrio No 0.26 in the mountains. Volume fluctuations enhance nutrient
Almoddvar No 0.33 movement, and a greater area of shallow water allows a
Arcos Yes 0.70 high production of macrophytes, and consequently, of
Barbate Yes 0.55 other organisms including fish. High fish abundance may
Bornos Yes 0.70 enhance Osprey foraging efficiency (Flook and Forbes
Gala No 0.10 1983). Deeper water inhibits photosynthesis, depressing
Celemin No 0.03 primary production (Ryder 1982). Rawson (1952) dem-
Charco Redondo No 0.33 onstrated a negative correlation between mean depth
Cordobilla No 0.55 and long-term fish production in reservoirs. The same is
El limonero No 0.43 true for Andalusian reservoirs, where productivity is
Gergal No 0.33 largely determined by mean depth and the level of eu-
Guadalcacin Yes 0.55 trophy (Sancho Royo and Granados 1988).
Guadarranque Yes 0.43 Sancho Royo and Granados (1988) investigated the re-
La Concepcion Yes 0.12 lationship between fish standing crop and characteristics
La Minilla No 0.26 of seven Andalusian reservoirs, six ofwhich were includ-
Los Hurones No 0.33 ed in the present study. These authors found that the
Pintado No 0.20 largest and most shallow reservoirs supported the highest
No
Retortillo 0.12 fish density (fish/m^).
Torre del Aguila No 0.43 Tolerance ofhuman activity depends on timing, inten-
Zahara Yes 0.33 sity, and frequency of activity and degree of habituation
to such activities (Odsjo and Sondell 1976, Swenson
1979, Van Daele and Van Daele 1982, Levenson and Kop-
nearest distances to transmission power line, to nearest lin 1984). Occupied reservoirs were closer to an urban
coastal point, and to nearest paved road. center than the unoccupied reservoirs. However, this may
After analyzing several combinations of variables, the be due to topographical constraints when towns were es-
simplest discriminant function with the highest correct tablished. No other human-activity indicator was related
classification was: to occupation by Ospreys, but this result should be taken
Ln (P/1 - P) = -6.59259 + 54.30499(number of with caution because we were using data on wintering
arms), which correctly classified 80% of cases: 92.3% of Ospreys that may respond to human activities in a differ-
unoccupied reservoirs and 57.1% of occupied (Wilks’s ent way than breeding Ospreys.
Lambda = 0.8, T) jg = 4.49, P< 0.04). The model clearly Wintering Ospreys in Spanish reservoirs do not appear
discriminated occupied versus unoccupied reservoirs on to choose reservoirs according to foraging perch avail-
the basis of number of arms of the reservoir. The reser- ability, as also was observed in Senegambia, Africa (Pre-
voirs with the highest probability of occupancy were Ar- vost 1982). Areas with high tree coverage will not neces-
cos (P = 0.70), Bornos (P = 0.70), Barbate (P = 0.55) sarily be occupied by Ospreys ifhabitat does not provide
and Guadalcacin (P = 0.55). an adequate food supply.
To compare univariate differences between occupied In Spain, Ospreys seem to choose reservoirs based on
and unoccupied reservoirs Mann-Whitney G-testwas used fish productivity over foraging perch availability or hu-
(Table 1) and these indicated a significant differences in man activity. In our analysis, the number of reservoir
number of arms and distance to nearest urban center. arms relative to total surface area was identified as a key
Occupied reservoirs had a fewer number of arms and a variable both because it is easy to derive and its relation
shorter distance to nearest urban center. to reservoir productivity.
Validation. Validation with the test set of reservoirs in- Management Implications. Using the discriminant
dicated that the discriminate function classified Osprey function analysis, we derived an estimate of the proba-
occupancy well. Only nine (21.4%) of 42 non-surveyed bility that one individual would be observed on a reser-
reservoirs were misclassified. voir under the conditions that existed during this study
This model developed for wintering Ospreys inAndalusia
Discussion
was focused on specific habitat characteristics (e.g., prey
The variable number of arms was negatively correlated and perch availability, human disturbance). Combining
with Osprey presence both in univariate test and in dis- this knowledge with an analysis of the status and devel-
criminant function analysis. High topographic relief, re- opment plans for the Andalusian reservoirs, environmen-
172 Short Communications VoL. 39, No. 2
tal management agencies would have an important tool us insights about looking for Ospreys. Comments of A.
to reduce the threats to migratory andwintering Ospreys. Harmata, P. Martin, and M. Pandolfi improved the man-
Results of the present study should be helpful for the uscript greatly.
Osprey reintroduction project in Spain. One advantage
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© 2005 The Raptor Research Foundation, Inc.
Introduced Animals in the Diets of the Ogasawara Buzzard, an Endemic Insular
Raptor in the Pacific Ocean
Yuka Kato^ and Tadashi Suzuki
Department ofBiological Sciences, Tokyo Metropolitan University, Minami-ohsawa Tl, Hachi-ohji,
Tokyo 192-0397Japan
Key Words: Common Buzzard; Buteo buteo toyoshimai; tal changes as are many other insular predators (e.g..
insular subspecies, diet, introduced animals; Bonin Islands; Cade andJones 1993). Therefore, ecological information
Ogasawara Islands. including dietary data are needed to develop conserva-
tion strategies for the population. However, little infor-
The Ogasawara buzzard {Buteo buteo toyoshimai) is an mation on the food habits of the Ogasawara buzzard are
insular subspecies ofthe Common Buzzard {B. buteo en- currently available.
),
demic to the Ogasawara (Bonin) Islands, in the Pacific Many researchers have investigated the diet ofthe con-
Ocean (Momiyama 1927, Ornithological SocietyofJapan tinental subspecies of the Common Buzzard, especially
2002). This hawk may be distinguished from a closely- in Europe. As a result, the Common Buzzard is well
related subspecies, the Japanese Common Buzzard {B. known to capture and consume various kinds of inver-
buteo japonicus), by its less brown or lighter plumage, a tebrates and small- to medium-sized vertebrates. Com-
longer bill, and shorter wings and tarsi (Momiyama mon prey include reptiles, birds, and rodents depending
1927). The distribution of the Ogasawara buzzard is very on environmental conditions (e.g.. Cramp and Simmons
restricted, and this hawk is classified as endangered in 1980, del Hoyo et al. 1994, Jedrzejewski et al. 1994,
Japan (Ministry of Environment 2002) Recently, Suzuki
. Swann and Etheridge 1995, Reif et al. 2001, Sergio et al.
and Kato (2000) reported on the abundance ofthe Oga-
2002
).
sawara buzzard on Chichijima, and estimated that less The native fauna ofthe Ogasawara (Bonin) Islandswas
than 85 pairs of this subspecies inhabited the Ogasawara
originally characterized by low species richness because
Islands.
of the island’s volcanic origin, and its small size and rel-
Insular raptors are likely to be sensitive to environmen-
atively great distance from the other islands and main-
land ofJapan (Tsuyama and Asami 1970). Human colo-
^ Email address: [email protected] nization of the islands began in the 1830s. After that