Use of European hare (Lepus europaeus) carcasses by an avian
scavenging assemblage in Patagonia
Alejandro Travaini1‘, Jose’ Antonio Dona’ zar1, Alejandro Rodriguez1, Olga Ceballos2, Martin Funes3,
Miguel Delibes4 and Fernando Hiraldo4
Estacio’ n Biolo’ gica de Don ana. CSIC. Apartado 1056. 41080 Sevilla, Spain
Grupo de Estudios Biolo’ gicos Ugarra. Carloss III 19, 31002 Pamplona, Spain
3
Centro de Ecologia Aplicada del Neuque’ n, Argentina
4
Estacio’ n Biolo’ gica de Don ana. CSIC. Apartado 1056. 41080 Sevilla, Spain
1
2
(Accepted 16 February 1998)
Abstract
We studied the use of European hare (Lepus europaeus) carcasses by avian scavengers in Argentinean
Patagonia. A total of 16 hare carcasses were placed in locations that could be observed without disturbing
birds feeding on them. Six avian species fed on these carcasses: chimango caracara (Milvago chimango),
crested caracara (Polyborus plancus), black vulture (Coragyps atratus), grey eagle-buzzard (Geranoaetus
melanoleucus), red-backed hawk (Buteo polyosoma) and cinereous harrier (Circus cinereus). Turkey vultures
(Cathartes aura), although abundant, never fed on the hare carcasses. The Andean condor also did not feed
on the carcasses. Mammals visited hare carcasses on only two occasions. Of the hare carcasses, 69% were
fully consumed during the first day of exposure and 25% in two days. There was no difference in the time
elapsed from the placement of the carcass and its detection by crested and chimango caracaras. There were
similar time periods from detection to first arrival, and time elapsed from first arrival to the start of feeding at
the carcass by crested and chimango caracaras. Hare body parts were consumed in different proportions by
crested and chimango caracaras whereas black vultures consumed the whole carcass. Interspecific hierarchies
at the carcass in a decreasing sequence of dominance were crested caracara > black vulture > chimango
caracara, coinciding with that expected from a body mass perspective. The scavenging species that consume
hare carcasses did not show a clear pattern denoting they were a highly interdependent assemblage in the
way described for scavengers in Africa.
Key words: hare carcasses, avian scavengers, Patagonia, Lepus europaeus, raptors
INTRODUCTION
Scavenging assemblages have been described for consumers of carcasses of rabbits (Oryctolagus cuniculus)
(Hewson, 1981), geese (Anser anser) (Hiraldo, Blanco &
Bustamente, 1991) and spawning salmon (Salmo salar)
(Stalmaster & Gessaman, 1984; Knight, Anderson &
Marr, 1991; Skagen, Knight & Orians, 1991; Hewson,
1995). All these studies have been carried out in
temperate zones of the Western Hemisphere where both
scavengers and the species they feed on are native. In
the western Patagonian steppe, there were few mediumsized mammals whose carcasses could be used by
facultative or obligated scavengers. This situation
‘All correspondence to A. Travaini at present address: Universidad
Nacional de la Patagonia Austral, Centro de Investigaciones de Puerto
Deseado, Almirante Brown y Colo’ n S/N, (9050) Puerto Deseado,
Santa Cruz, Argentina
changed at the end of the 19th century when the
European hare (Lepus europaeus) was introduced in
Chile and Argentina for hunting purposes (Grigera &
Rapoport, 1983). Soon after their introduction hares
spread throughout Argentinian Patagonia at a dispersal
rate of about 20 km/year (Grigera & Rapoport, 1983).
At present, the European hare inhabits all of continental
Patagonia where it could reach winter densities of more
than 2000 individuals per km2 (Novaro et al., 1992).
The European hare in Patagonia has a mean body
weight of 3250 g (Amaya, 1979) and its reproductive
season lasts from the end of August to the end of
January (Amaya, 1979; Amaya, Alsina & Brandani,
1979). Thus all size and age classes are available to
predators and scavengers during spring. In our study
area at least seven mammalian carnivores (two canids,
three felids, two mustelids), two edentates, and 11
raptorial (three nocturnal and eight diurnal raptors)
species consume hares, either as a live prey or as carrion
(Novaro, 1991; Hiraldo, Donazar et al., 1995). Normal
mortality sources of hare are road traffic casualties,
adverse meteorological conditions (Alsina & Brandani,
1979), commercial hunting, disease, and predation.
Our objective was to describe how European hare
carcasses are consumed by an assemblage of vertebrate
species in Patagonia. This description includes species
detecting, arriving at, and consuming the carcass, as
well as their interespecific hierarchies while feeding, the
carcasss partitioning, and some frequent feeding behaviours. Finally, we discuss whether our results agree
with those expected from the existence of an interdependent assemblage of species consuming carrion.
STUDY AREA AND METHODS
The study area, considered as ‘Precordillera’ by some
authors (Pearson & Pearson, 1982, and references
therein), was located in north-western Patagonia
(70°30’—71°30’W; 39°30’— 40°20’S). The weather is dry
and cold, with frost throughout most of the year and
frequent snowfalls in winter. Topographically, the area
consists of plains at 800—900 m above sea level, dissected
by steep rugged valleys and large rivers.
We conducted this study in spring, from October to
December 1991. We weighed each carcass before
placing it out. We used 10 different feeding stations,
each at a location that we could observe from a distance
without disturbing the feeding birds. No raptorial
species were able to lift the intact hare carcasses so, by
necessity, the birds fed on or dismembered them while
at the feeding station. We obtained intact fresh hare
carcasses mainly from roads (11), and also from local
hunters (5). Road-killed European hares were abundant
(3—6 hares per 35 km/day) in our study area. This, and
the fact that most of our carcasses were collected in the
road, means that our experimental study did not result
in a significant increase of the food supply of avian
scavengers. Furthermore, we assume that avian scavengers did not increase in our study area during our
experiment. From simultaneous studies we know the
chimango caracara (Milvago chimango) is 5—8 times
more abundant than the crested caracara (Polyborus
plancus) and the black vulture (Coragyps atratus), and
10—12 times more abundant than the red-backed hawk
(Buteo polyosoma) and the grey eagle-buzzard (Geranoaetus melanoleucus) (Donazar et al., 1993; Travaini
et al., 1995).
To minimize disturbing the birds, we observed
carcasses with binoculars and a telescope from a vehicle
or a natural blind (rocks or vegetation) approximately
300 m from the feeding station. We recorded the behaviour of birds at the carcass with an audio tape
recorder. At the end of the day, or when the whole hare
was apparently eaten, we visited the feeding station and
weighed the carcass remains. We considered that a
carcass was completely eaten when: (1) only bone and
skin remained; or (2) remains weighed less than 20% of
the fresh weight. If any carcass was not fully eaten
during the first day, we left it and resumed the observations in the morning of the following day.
We recorded every species visiting and feeding at the
carcass as well as their arrival sequence. We also
recorded the time elapsed between placement of each
carcass in the station and: (1) first detection (we noticed
when a bird detected the carcass by observing its
behaviour, e.g. changing its flying direction while
passing near it); (2) first arrival; (3) first feeding event;
(4) carcass opening (exposure of viscerae or digestive
tract); and (5) departure of the last bird when no more
food was available at the feeding station. We assessed
differences between species in these times by using
t-tests or the Mann—Whitney U test when samples did
not conform to parametric conditions. At 10-min intervals we recorded the number and species of individuals
close to the carcass and their individual positions, in the
carcass if they were within 1 m, or out of the carcass if
they were farther away, and whether they were feeding
or not. Whenever we were able to identify individuals,
we measured the time between their arrival and their
departure, i.e. the duration of individual feeding
periods. For each species, the length of permanence
periods (min) was defined as the number (x10) of
consecutive occurrences in the 10-min interval samples.
In social species such as black vultures, individual
feeding periods were difficult to measure. Then, for each
carcass, the weighted average time one individual spent
at the feeding station was derived from permanence
time and group size.
In order to quantify relative carcass consumption by
different species we used a consumption index, C,
defined as:
PxF
C
N
where P is the permanence time of the species at the
carcass, F is the average individual feeding period, and
N is the average number of individuals present at the
feeding station. The index C is an estimate of the
number of rations that a given species takes from the
carcass. We hypothesized that the amount of food eaten
per individual feeding period is a positive function of
body size. So, it was predicted that carcasses would be
depleted faster by heavier scavenger species. To
compare C values between species, we converted them
into consumption units, based on a C value of one for
the smallest species, the chimango caracara. According
to the average weights of species (Del Hoyo, Elliot &
Sargatal, 1994), the conversion factors into consumption units were 3.2 for the red-backed hawk, 4.7 for the
crested caracara, 5.1 for the black vulture, and 6.8 for
the grey eagle-buzzard. Whenever possible we recorded
on which part of the carcass birds were feeding, and
which parts they carried when they left the feeding
station.
In order to determine interspecific hierarchies, we
observed foraging interactions and recorded intra- and
interspecific aggressive interactions ad libitum (Altmann,
1974). We considered an aggression successful when the
recipient was displaced from food or space by the
aggressor. We also assessed the ‘directionality’ of aggressive interactions, defined as the probability that one
aggressor selects a specific recipient (from the same or a
different species) as the recipient of aggression, considering all individuals present at the carcass during that
interaction (recipient availability). We estimated this
probability only from those cases where at least two
different species and three different individuals were
simultaneously present at the carcass. The Chi square
test (Siegel & Castellan, 1988) was used to compare
observed and expected interaction frequencies.
RESULTS
Species consuming the carcass
Sixteen hare carcasses (x weight ± SD) (3060 ± 987 g)
were left singly in 10 different feeding stations. Chimango caracara fed on 15 hare carcasses, crested
caracara on 10, black vulture on eight, grey eaglebuzzard on two, and red-backed hawk and cinereous
harrier (Circus cinereus) on only one. On one occasion
one adult female Andean condor (Vultur gryphus)
landed near a hare carcass but she was chased away by a
group of at least 60 black vultures and five immature
crested caracaras when she tried to feed. Turkey vultures (Cathartes aura) never fed on hare carcasses. Four
hare carcasses were visited and partly eaten by only one
species (chimango caracara), another four carcasses
were eaten by two species, while three species ate on
seven and four on one carcasses. The maximum number
of species simultaneously present at a carcass was four
(crested and chimango caracaras, black vulture and grey
eagle-buzzard). Up to 60 black vultures were simultaneously recorded at a carcass. Maximum numbers
of crested and chimango caracaras were six and 18,
respectively.
Every species in this assemblage, even the small
chimango caracara, was able to open an intact hare
carcass, as well as to fully eat it alone. However, the
chimango caracara only completely ate one (20%) out of
five hares visited by no other species, or only briefly
visited by one red-backed hawk. Interestingly, chimango
caracaras never opened the abdominal cavity of carcasses, and opened the thoracic cavity of the carcass and
ate the heart only once.
Mammals fed on hare carcasses on only two occasions.
A domestic dog (Canis familiaris) took away a partially
eaten carcass, after 4 h and 50 min of observation,
displacing a chimango caracara and a crested caracara to
do so. During a night between the first and second day of
observation, footprints indicated that a Patagonia
haired-armadillo (Chaetophractus villosus) and a culpeo
fox (Dusicyon culpaeus) visited and fed on a carcass.
Eleven hare carcasses (69%) were fully consumed
during the first day of exposure, a further four
(25%) were consumed in two days, and one was abandoned, practically untouched, after three days of
observation.
Detection, arrival and feeding behaviour
We determined the species that first detected 12 of the
carcasses. The chimango caracara detected the carcass
first seven times, the crested caracara four times and the
black vulture once. There was no difference in the time
elapsed from the placement of the carcass and its
detection between crested (x ± SD min, sample size;
49.0 ± 43 min, 4) and chimango (31.0 ± 24 min, 7)
caracaras (t 0.90, d.f. 9, P 0.39). Of the 16 times we
determined which species arrived at the carcass chimango caracaras were first 14 times; the crested
caracara twice. There were similar time periods from
detection to first arrival between crested (27 ± 21 min, 2)
and chimango (63.8 ± 66 min, 10) caracaras (t 0.75,
d.f. 10, P 0.50). On 11 of 15 occasions chimango
caracaras were the first to feed on the carcass, crested
caracaras were first on the other four times. There was
no difference in the time elapsed from first arrival to the
start of feeding at the carcass between crested (4.5 ± 3
min, 4) and chimango (5.6 ± 13 min, 11) caracaras
(Mann—Whitney U 12.5, P 0.23). Crested caracaras
first opened the hare carcass exposing viscera and
digestive tract seven times. The time elapsed from the
start of feeding to carcass opening was 8.5 ± 9 min
(n 4) for the crested caracara.
The average feeding periods for individual chimangos
and crested caracaras were 13 min (SE 0.91; n 138)
and 14 min (SE 1.36; n 98), respectively. The difference were not significant (chimango, F12,125 1.27;
P 0.24; crested, F 9,88 1.42; P 0.19), even though
carcasses were quite different in fresh weight, location,
time needed to be fully eaten, number of species and
number of individuals which fed on them, and time
spent at the carcass by these animals. Individuals fed,
on average, the same length of time, whether or not
another species of higher status visited the carcass
(chimango, F1,136 0.63; P 0.44; crested, F1,96 0.47;
P 0.50). For black vultures only average estimates
could be made, and for other species there were to few
data to analyse individual feeding periods.
Scavengers regularly carried parts of carcasses away
from the feeding station. Chimango caracaras transported muscle five times (71%), and viscerae and skin
once each. Crested caracaras transported viscerae 10
times (56%), muscle six times (33%), and skin twice
(11%). In both species the frequencies of transported
type of hare bits were not significantly different
(G 3.97, P > 0.05). Usually, caracaras carried food
several times in sequence in the same direction, suggesting they were supplying the nest (this was confirmed
in 85% of cases for crested caracaras).
Adult caracaras often defended the carcass on which
they fed. When only two individuals of the same species
(presumably an adult pair) were at the carcass, we saw
few aggressive interactions. Both birds participated in
food handling and vigilance. One crested caracara
stayed at the carcass and interacted aggressively
towards individuals of other species, while the other
carried food to the nest. At two feeding stations, a
breeding pair of crested caracaras chased every bird
arriving at the carcass even when neither of the territory
holders was feeding on it. In contrast, immature birds
never co-operated while feeding.
Chimango caracaras behaved relatively secretly at the
carcass. Some individuals walked to the carcass from a
distance of up to 100 m. Chimango caracaras often hid
themselves under nearby plants or crouched down
beside the carcass, sometimes for more than 20 min.
During most of these events at least one other raptor
was flying nearby and, sometimes, the hidden caracara
was spotted and subsequently attacked.
Finally, when chimango caracaras, in groups or
alone, contacted the carcass for the first time they
usually showed neophobic behaviour: they repeatedly
touched the hare and suddenly flew or jumped back,
examined the carcass carefully from all sides, and sometimes went away without eating.
Carcass partition among scavengers
We divided hare body parts into four categories: viscerae, muscle, skin, and small bits of meat scattered
around the carcass. Chimango caracaras ate mainly
muscle 44 times (54%), viscerae 21 times (28%), bits 11
times (15%) and skin twice(3%). Crested caracaras consumed viscerae and muscle each 19 times (43%), skin 5
times (11%), and ate sparse bits only once (2%). These
frequencies differed significantly between both species
(G 127.35, d.f. 3, P < 0.001).
Regression analysis indicated that differences in fresh
weight did not influence either the number of individuals
per species or the overall number of individuals feeding
on a carcass. Similarly, consumed biomass was not
related to the average number of individuals of each
species feeding at the carcass. However, there was a
significant correlation between consumed biomass and
consumption units (r 0.616; P 0.03). This correlation
allowed us to calculate the percentage of biomass eaten
by each species (Table 1). When present, black vultures
consumed on average 64% of hare biomass, crested
caracaras (35%), and chimango caracaras (25%). Taking
into account only carcasses where all three species fed
together, figures were 54%, 40%, and 6%, respectively
(Table 1). These (arcsin transformed) proportions did
not differ significantly between species (F2,9 3.85,
P 0.062).
Interspecific hierarchies
We estimated interspecific hierarchies based on 556
interspecific interactions (Table 2). Chimango caracaras
were always displaced by other species. Crested caracaras were able to dominate conspecifics, chimango
caracaras, and black vultures. Black vultures were also
successful in most of their attacks. Crested caracara and
black vulture performed and received a similar proportion of successful interactions between them (Fisher’s
Table 1. The average percentage of consumed biomass (expressed as consumption units) by the main three scavenger
species when present, and when feeding together at hare
carcasses
When present
n
Mean
SE
Chimango
caracara
Crested
caracara
Black
vultures
7
25.4
13.2
8
35.0
8.9
6
64.3
12.6
39.5
28.4
54.3
32.5
Three species together (n 4
Mean
6.3
SD
4.1
exact test, P > 0.05) showing no clear hierarchical relationship (Table 2). Finally, data for the grey eaglebuzzard were not enough to obtain any clear pattern.
Following Kruuk (1967) we estimated an aggressiveness index by dividing the number of interspecific
attacks for each species by the total number of attacks
(inter- and intraspecific; Table 2). The resulting hierarchy, in a decreasing sequence is: crested caracara >
black vulture > chimango caracara.
Except for the crested caracara, most of the observed
interactions were directed toward members of the same
species (Fig. 1). Crested caracaras directed less fights
than expected towards conspecifics and more than
expected towards other species (o2 11.88, d.f. 3,
P < 0.01) (Fig. 1). Both the chimango caracara and the
black vulture directed more intraspecific and fewer
interspecific interactions, respectively, than expected
(chimango caracara o2 10.7, d.f. 2, P < 0.005; black
vulture o2 82.5, d.f. 2, P < 0.001). Observations for
the grey eagle-buzzard were too few to allow any
statistical conclusion.
Discussion
Raptorial birds were the main consumers of European
hare carcasses. Obligate scavengers were the chimango
caracara, the Andean condor, and turkey and black
vultures. Facultative scavengers were immature grey
eagle-buzzard, both adult and immature crested caracara, cinereous harrier, red-backed hawk, culpeo fox,
and grey fox. All avian scavengers visiting the feeding
stations were previously observed at road killed hares
(mainly chimango and crested caracaras, but also black
vultures and grey eagle-buzzards). Consumption by
mammals was negligible, probably because they had
little opportunity to feed on them during the night.
Raptorial birds also consumed much more of the
carcass than mammals did in studies of Old and New
World vultures (Houston, 1974, 1988; Hiraldo, Blanco
et al., 1991). In our study area one mammalian carnivore, the Andean hog-nosed skunk (Conepatus chinga),
and two edentates, the Patagonian haired-armadillo and
the pichi (Zaedyus pichiy) occasionally eat dead hares.
Table 2. Inter- and intra-specific fights observed at hare carcasses in Argentinean Patagonia during the spring (October to
December) 1991. The percentage of attacks won are given in parentheses. Body masses were taken from Del Hoyo et al., 1994)
Attacked (body mass, g)
Chimango caracara
(289—300)
Crested caracara
Attacker
Chimango caracara
Crested caracara
Black vulture
Grey eagle-buzzard
42 (88)
99 (100)
1 (100)
4 (100)
3 (0)
59 (90)
20 (80)
Aggressiveness
0.07
0.76
Black vulture
(1100—1900)
Grey eagle-buzzard
(2000)
86 (94)
241 (100)
1 (100)
0.08
Polyborus plancus
Coragyps atratus
100
100
80
80
1117
60
0.2
1887
60
40
40
559
525
443
20
20
230
7
Frequency
0
0
POLPLA
GERMEL
CORATR
MILCHI
POLPLA
Milvago chimango
CORATR
MILCHI
Geranoaetus melanoleucus
100
100
16
47
80
80
60
60
8
39
40
40
14
20
20
0
0
POLPLA
CORATR
POLPLA
MILCHI
MILCHI
Recipient species
Fig. 1. Directionality, expressed as percentage of fights directed to each species, for four different species while feeding at hare
carcasses in Argentinean Patagonia, spring (October to December) 1991. Open and black bars correspond to observed and
expected frequencies, respectively. Number at top of each bar
total number of fights used to construct bars. POLPLA,
Polyborus plancus; GERMEL, Geranoaetus melanoleucus; MILCHI, Milvago chimango; CORATR, Coragyps atratus.
Our results agree well with independent information on
food habits for the same species in the same study area
and season. European hare comprise up to 66% (per
cent of occurrence) of the adult’s and up to 60% of
nestling crested caracara’s diet (Travaini et al., pers.
obs.). Black vultures consume mainly ungulates and
secondarily European hare in our study area (authors’
unpublished data). The chimango caracara has less than
3% of hare in its diet. This agrees well with its low
hierarchy at the carcass. Hares comprise up to 60% of
the diet of the grey eagle-buzzard and 14% of the diet of
the red-backed hawk (per cent occurrence) (Hiraldo,
Donazar et al., 1995). Both species are active predators
(Jime’ nez & Jaksic, 1989, 1990, 1991; Jime’ nez, 1995) that
occasionally scavenge on hare carcasses.
Every scavenging species in our study was large
enough to open and consume hare carcasses alone. The
smallest species, the chimango caracara, behaved secretly after detecting the hare carcass, which probably
reduced the probability that other species would find the
carcass by observing feeding chimangos (Ward &
Zahavi, 1973; Knight & Knight, 1983). This fact departs
from other scavenger assemblages where bigger species
are attracted to the carrion by the smaller ones (Kruuk,
1967; Houston, 1974; Wallace & Temple, 1987), and
where food is available to smaller species only when the
skin of carcasses is torn (Kruuk, 1967; Skagen et al.,
1991). Lower ranked species in the aggressive hierarchy
can feed unmolested only if they discover carcasses first.
In addition, even though single crested caracaras can
defend a carcass from a single black vulture, a group of
vultures can displace a single caracara.
Higher ranked species should arrive later, after the
presence of lower rank birds evidenced that the carcass
constitutes a safe source of food (Marzluff & Heinrich,
1991). Accordingly, checking for safety was mainly
done by chimango caracaras. However, in our study
both the most (crested caracara) and the least (chimango caracara) aggressive species showed similar
tendencies in detecting and starting to feed at the
carcass. The higher proportion of chimango caracaras
detecting the carcass (64%) against that of crested
caracaras (34%) could simply be a consequence of a
higher density of the former species (Donazar et al.,
1993; Travaini et al., 1995).
As all species can eat the whole carcass, none of them
can be considered specialized in exploiting a specific
fraction of the hare body, as occurs in structured scavenger assemblages (e.g. Kruuk, 1967). However,
chimango caracaras ate more bits around the hare and
less viscerae than crested caracaras, probably as a result
of interference competition at the carcass. Viscerae (soft
and easy to detach) may be a valuable food to be
transported to the nest. Once a pair of crested caracaras
opened the thoracic or abdominal cavities, adults rapidly
took turns to defend the carcass and to transport food to
the nest (up to a rate of one trip every 2 min).
The observed hierarchy conforms to that expected
from a body mass perspective. A similar pattern was
observed in other scavenger assemblages in East (Kruuk
1967) and South Africa (Ko nig, 1983) and Spain
(Alvarez, Arias de Reyna & Hiraldo, 1976; Hiraldo,
Blanco et al., 1991). The fact that both chimango
caracaras and black vultures fight more than expected
with conspecifics results from the fact that chimangos
are subordinate to other species and that black vultures
forage in a group (Kruuk, 1967). The dominant crested
caracara, on the other hand, primarily attacks individuals of other species.
The species that consume hare carcasses in Patagonia
did not divide the carcasses in ways that suggest assemblage. Because all species can open and consume all
parts of a hare carcass, none of the species is dependent
on others. Therefore, their situation is based on hierarchical dominance, which is correlated with body mass.
The European hare is a recently introduced species.
In our study area there were no other similar-sized
mammal species before this introduction. Thus, a structured scavenger guild could not have already evolved.
One possibility is that species scavenging on hare
carcasses belong to a bigger assemblage, i.e. the consumers of wild ungulates, that include other species such
as as the Andean condor. The existence of a bigger and
co-evolved scavenging assemblage should be confirmed.
Acknowledgements
Our special thanks to O. Monsalvo for his field
assistance. G. Alena, G. and M. Anz, R. Cordero,
V. Soleno, the administrators of the Estancias Cerro los
Pinos, Serranias de Lole’ n, Collo’ n-cura and Chimehuin,
permitted us to work on their land. Logistic support was
provided by the Centro de Ecologia Aplicada del
Neuque’ n (Argentina); we thank A. del Valle and
A. Guinazu’ from the CEAN for their constant kind
assistance. R. Rodriguez-Estrella, R. Hewson, G. H.
Orians and C. D. Fitzgibbon critically revised an original
draft of the manuscript. Financial support was provided
by the Instituto de Cooperacio’ n Iberoamericana and the
Ministerio de Asuntos Exteriores (Spain) through the
Programa de Cooperacio’ n Cientifica con Iberoame’ rica.
The senior author has a post-doctoral fellowship from
the Ministerio de Educacio’ n y Ciencia (Spain).
REFERENCES
Alsina, G. & Brandani, A. (1979). Population dynamics of the
European hare in Patagonia, Argentina. In Proceedings of the
World Lagomorph Conference: 486—492. Myers, K. &
MacInnes, C. D. (Eds). Guelph: University of Guelph.
Alvarez, F., Arias de Reyna, L. & Hiraldo, F. (1976). Interactions
among avian scavengers in southern Spain. Ornis Scand. 2:
215—226.
Altmann, J. (1974). Observational study of behaviour: sampling
methods. Behaviour 49: 227—267.
Amaya, J. W. (1979). The European hare in Argentina. In
Proceedings of the World Lagomorph Conference: 493—494.
Myers, K. & MacInnes, C. D. (Eds). Guelph: University of
Guelph.
Amaya, J. W., Alsina, M. G. & Brandani, A. B. (1979). Ecologi’a
de la Liebre Europea Lepus esuropaeus P. Parte 2. Informe
Te‘ cnico No. 9. Bariloche: INTA Bariloche.
Del Hoyo, J., Elliot, A. & Sargatal, J. (1994). Handbook of the
birds of the world, 2. Barcelona: Lynx Editions.
Donazar, J. A., Ceballos, O., Travaini, A. & Hiraldo, F. (1993).
Roadside raptor surveys in the Argentinean Patagonia.
J. Raptor Res. 27: 106—110.
Grigera, D. E. & Rapoport, E. H. (1983). Status and distribution
of the European hare in South America. J. Mamm. 64: 163—166.
Hewson, R. (1981). Scavenging of mammal carcases by birds in
West Scotland. J. Zool. (Lond). 194: 525—537.
Hewson, R. (1995). Use of salmonid carcasses by vertebrate
scavengers. J. Zool. (Lond.) 235: 53—65.
Hiraldo, F., Blanco, J. C. & Bustamante, J. (1991). Unspecialized
exploitation of small carcasses by birds. Bird Study 38: 200—
207.
Hiraldo, F., Donazar, J.A., Ceballos, O., Travaini, A., Bustamante, J. & Funes, M. (1995). Breeding ecology of a Grey
Eagle-buzzard population in Patagonia. Wilson Bull. 107: 675—
685.
Houston, D. C. (1974). The role of griffon vultures Gyps africanus
and Gyps ruppellii as scavengers. J. Zool. (Lond). 172: 35—46.
Houston, D. C. (1988). Competition for food between Neotropical
vultures in forest. Ibis 130: 403—417.
Jime’ nez, J. E. (1995). Historia natural del aguilucho Buteo
polyosoma: una revisio’ n. Hornero 14: 1—9.
Jime’ nez, J. E. & Jaksic, F. M. (1989). Behavioral ecology of grey
eagle-buzzards, Geranoaetus melanoleucus in central Chile.
Condor 91: 913—921.
Jime’ nez, J. E. & Jaksic, F. M. (1990). Historia natural del l3guila
Geranoaetus melanoleucus: una revisio’ n. Hornero 13: 97—110.
Jime’ nez, J. E. & Jaksic, F. M. (1991). Behavioral ecology of redbacked hawks in central Chile. Willson Bull. 103: 132—137.
Knight, R. L., Anderson, D. P. & Marr, N. V. (1991). Responses
of an avian scavenging guild to anglers. Biol. Conserv. 56: 195—
205.
Knight, S. K. & Knight, R. L. (1983). Aspects of food finding by
wintering bald eagles. Auk 100: 477—484.
Konig, C. (1983). Interspecific and intraspecific competition for
food among Old World vultures. In Vulture biology and
management: 153—171. Wilbur, S. R. & Jackson, J.A. (Eds).
Berkeley: University of California Press.
Kruuk, H. (1967). Competition for food between vultures in East
Africa. Ardea 55: 171—193.
Marzluff, J. M. & Heinrich, B. (1991). Foraging by common
ravens in the presence and absence of territory holders: an
experimental analysis of social foraging. Anim. Behav. 42: 755—
770.
Novaro, A. J. (1991). Feeding ecology and abundance of a harvested
population of culpeo fox (Dusicyon culpaeuus) in Patagonia. MSc
thesis, University of Florida, Gainesville.
Novaro, A. J., Capurro, A. F., Travaini, A., Funes, M. C. &
Rabinovich, J. E. (1992). Pellet-count sampling based on
spatial distribution: a case study of the European hare in
Patagonia. Ecol. Aust. 2: 11—18.
Pearson, O. P. & Pearson, A. K. (1982). Ecology and biogeography of the southern rainforest of Argentina. In Mammalian
biology of South America: 129—142. Mares, A. M. & Genoways,
H. H. (Eds). Special Publication Series 6, Pittsburg: Pymatuning Laboratory of Ecology.
Siegel, S. & Castellan, N. J., Jr (1988). Nonparametric statistics
for the behavioral sciences. 2nd edn. New York: McGraw-Hill.
Skagen, S. K., Knight, R. L. & Orians, G. H. (1991). Human
disturbance of an avian scavenging guild. Ecol. Monogr. 1:
215—225.
Stalmaster, M. V. & Gessaman, J.A. (1984). Ecological energetics
and foraging behavior of overwintering Bald Eagles. Ecol.
Monogr. 54: 407—428.
Travaini, A., Rodriguez, A., Ceballos, O., Donazar, J.A. &
Hiraldo, F. (1995). Roadside raptor surveys in central
Argentina. Hornero 14: 64—66.
Wallace, M. P. & Temple, S.A. (1987). Competitive interactions
within and between species in a guild of avian scavengers. Auk
104: 290—295.
Ward, P. & Zahavi, A. (1973). The importance of certain assemblages of birds as ‘information-centres’ for food-finding. Ibis
115: 517—534.