Use of European hare (Lepus europaeus) carcasses by an avian scavenging assemblage in Patagonia

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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

1 Estacio’ n Biolo’ gica de Don ana. CSIC. Apartado 1056. 41080 Sevilla, Spain

2 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
(Accepted 16 February 1998)


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

Scavenging assemblages have been described for consu- mers 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 medium- sized 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 beha- viours. Finally, we discuss whether our results agree with those expected from the existence of an interdepen- dent assemblage of species consuming carrion.


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 scaven- gers 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 (Gera- noaetus 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 beha- viour 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 observa- tions 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 inter- vals 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:
C P x F 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 consump- tion 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 aggres- sive interactions, defined as the probability that one aggressor selects a specific recipient (from the same or a different species) as the recipient of aggression, consid- ering 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.

Species consuming the carcass

Sixteen hare carcasses (x weight ± SD) (3060 ± 987 g) were left singly in 10 different feeding stations. Chi- mango caracara fed on 15 hare carcasses, crested caracara on 10, black vulture on eight, grey eagle- buzzard 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 vul- tures (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 simul- taneously 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 car- casses, 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 aban-

doned, 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 chi- mango 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 differ- ence 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 trans- ported 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, sug- gesting 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 some- times went away without eating.

Carcass partition among scavengers
We divided hare body parts into four categories: vis- cerae, 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 con- sumed 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 cara- caras 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 propor- tion of successful interactions between them (Fisher’s

Table 1. The average percentage of consumed biomass (ex- pressed as consumption units) by the main three scavenger species when present, and when feeding together at hare carcasses

Chimango Crested Black caracara caracara vultures
When present

n 7 8 6

Mean 25.4 35.0 64.3

SE 13.2 8.9 12.6

Three species together (n 4

Mean 6.3 39.5 54.3

SD 4.1 28.4 32.5

exact test, P > 0.05) showing no clear hierarchical rela- tionship (Table 2). Finally, data for the grey eagle- buzzard were not enough to obtain any clear pattern.

Following Kruuk (1967) we estimated an aggressive- ness index by dividing the number of interspecific attacks for each species by the total number of attacks (inter- and intraspecific; Table 2). The resulting hier- archy, 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.

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 cara- cara, 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 carni- vore, 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 Crested caracara Black vulture Grey eagle-buzzard

Attacker (289—300) (1100—1900) (2000)
Chimango caracara 42 (88) 3 (0)

Crested caracara 99 (100) 59 (90) 86 (94) Black vulture 1 (100) 20 (80) 241 (100)

Grey eagle-buzzard 4 (100) 1 (100)

Aggressiveness 0.07 0.76 0.08 0.2

Polyborus plancus Coragyps atratus




60 1117












Milvago chimango Geranoaetus melanoleucus




80 80

60 60 8
40 40

20 14 20



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 se- cretly 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 (chi- mango 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 sca- venger 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 indivi- duals of other species.

The species that consume hare carcasses in Patagonia did not divide the carcasses in ways that suggest assem- blage. 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 hier- archical 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 struc- tured scavenger guild could not have already evolved. One possibility is that species scavenging on hare carcasses belong to a bigger assemblage, i.e. the con- sumers 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.


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).


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