Taphonomy of the Accumulations Produced by Caracara plancus

P R O ME T H E US P R E S S / P A L A E O N T O L O G I C A L N E T W O R K F O UN D A T I O N
Journal of Taphonomy
(TERUEL)
2009
Available online at www.journaltaphonomy.com
Montalvo & Tallade
VOLUME 7 (ISSUE 2-3)
Taphonomy of the Accumulations Produced
by Caracara plancus (Falconidae).
Analysis of Prey Remains and Pellets
Claudia I. Montalvo*, Pedro O. Tallade
Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa
Uruguay 151, 6300 Santa Rosa, La Pampa, Argentina
Journal of Taphonomy 7 (2-3) (2009), 235-248.
Manuscript received 30 September 2008, revised manuscript accepted 3 February 2009.
Caracara plancus (Falconidae) is a diurnal raptor bird, described as an opportunist that feeds on carrion
and a variety of live preys, including rodents. Based on the skeletal remains of rodents recovered from
pellets produced by this bird, an analysis of the modifications occurred on those bones was carried out,
concluding that they were important. Along with pellets, scattered rodents prey remains not digested,
collected in the same sampling area, under the roosting, were analyzed. The comparison of the data from
pellets and that from uneaten prey remains indicates that southern caracara would perform a certain
selection over different body parts of predated rodents, discarding mainly the cranial regions. The
ingested osseous remains, showing evidence of breakage and digestion, could accumulate together with
the skeletal elements that, which constitute the remains of prey, with particular signs of breakage but
without signs of digestion. These findings are particularly relevant in order to avoid missininterpretations
of this kind of accumulations, which are not mixtures produced by several predators but only one
predator with a particular pattern of ingestion. Consequently, when zooarchaeological or paleontological
records from the Pampean region are analyzed, it is very important to consider the fact that these birds of
prey could have contributed to the accumulation of micromammal bones, with skeletal elements coming
both from pellets and prey remains.
Keywords: TAPHONOMY, PELLETS, PREY REMAIN SELECTION, CARACARA PLANCUS,
ARGENTINA
Introduction
In the Pampean region, Argentina, there are
some archaeological and paleontological sites
that are very rich in micromammal bones,
especially rodents. It is important to document
the processes and agents that may have enabled
preservation of that record. Microvertebrate
teeth and bones can be added to the record
through different processes of accumulation.
Article JTa089. All rights reserved.
*E-mail: [email protected]
235
Taphonomy of the accumulations produced by Caracara plancus
Natural disaggregation of pellets produced by
raptor birds and scats of carnivores are important
processes of accumulation. Taphonomic studies
of recent accumulations produced by different
predators can contribute to establish their
diagnostic characteristics, which can be
extrapolated to other records. Some studies
have previously dealt with taphonomic analysis
of different predators in the Pampean area
(Gómez, 2005, 2007, Montalvo et al., 2007,
2008).
Among birds of the family Falconidae,
the genus Caracara shows a very wide
distribution in South America, with two
continental species, C. cheriway in the north
and C. plancus (southern caracara) in the
south (Dove & Banks, 1999). It is a solitary
bird, although it can be also seen in pairs. In
this study, the alterations produced on the
Figure 1. Geographic location of Santa Rosa in La Pampa
province, Argentina.
bones of rodent preys by southern caracara
were analyzed on the basis of pellets and
uneaten prey remains scattered throughout
the sampling area (under the roosting), west
of Santa Rosa city, La Pampa province,
Argentina.
Caracara plancus is a dietary
opportunist that feeds on carrion and a
variety of live preys, including rodents
(Travaini et al., 2001 and references therein).
However, several previous analyses have
suggested that the carrion constitutes only
20-40% of their diet (Rodríguez Estrella &
Rivera Rodríguez, 1997, Travaini et al., 2001,
Morrison & Pias, 2006, Vargas et al., 2007),
and the rest of the diet consists of live
animals. Rodríguez Estrella and Rivera
Rodríguez (1997) found that hunted preys
had a body mass less than 500 g. Among the
small vertebrates, rodents, lagomorphs, birds,
amphibians, reptiles, and fishes are mentioned
as usual preys. Pellets produced by this bird
accumulate beneath the nests or below the
roosting; in these areas it is also common to
find prey remains that have not been consumed.
Studies based on the content of
vertebrates recovered from pellets produced
by southern caracara and its prey remains
are restricted in general to diet analyses
(Rodríguez Estrella & Rivera Rodriguez, 1997,
Travaini et al., 2001, Morrison & Pias,
2006, Vargas et al., 2007). In the particular
case of the bones contained in pellets, little
is known about the digestive modifications
that are produced by this predator. Gómez
(2007) experimentally evaluated the digestive
modifications produced by a southern caracara
in captivity, feeding on rodents. The results,
based on two recovered pellets, were very
scarce, reason why it was concluded that the
southern caracara “is above all a scavenger
and, when hunting, it destroys all the bones
pulling out the flesh” (Gómez, 2007).
236
Montalvo & Tallade
For the taphonomic analysis presented
in this paper, the rodent skeletal remains from
pellets were reviewed following the proposal
of Andrews (1990) and Fernández Jalvo &
Andrews (1992). This allowed the inclusion
of southern caracara under the categories of
modification previously proposed by Andrews
(1990). In addition, rodent prey remains not
consumed were also analyzed in order to
evaluate which body parts had been discarded.
Vargas et al. (2007) indicated that, in open
environments, these predators accumulate
prey remains in nesting and roosting sites.
This analysis shows that these kind of remains,
without evidence of digestion, can accumulate
together with the digested remains from pellets.
We suggest that this mode of accumulation
is a working hypothesis to explain some
peculiarities of the zooarchaeological and
paleontological microvertebrate associations
in the Pampean region.
Study area
The studied sample was collected in the west
of Santa Rosa city (36°37’10’’S, 64°19’45’’W),
La Pampa Province, Argentina (Fig. 1). The
area lies within the Espinal Phytogeographic
Province (Cabrera, 1976), where the "caldén"
(Prosopis caldenia) forest is predominant,
with psammophyle grassland, scrubland,
and halophyle grassland. It shows important
changes resulting from agricultural activities,
the proximity to an urban center, and the
presence of plantations of eucalyptus (Eucalyptus
sp.) and “tamariscos” (Tamarix gallica).
Materials and methods
The sample produced by a couple of southern
caracara, in a non reproductive season, was
collected weekly from March to June 2005.
Pellets (67) and uneaten prey remains (65)
were preserved in paper envelopes and
stored in a dry and fresh place. Manual
disaggregation of each pellet allowed the
separation of bone remains, horny material,
hair, and feathers. All pellets contained
vertebrate bones, but only those containing
rodent bones are discussed in this paper.
Materials were observed under a Leica Ms5
binocular microscope, and some of them
were photographed under a Jeol 35 CF at 8 KV
at the Unidad de Administración Territorial
(UAT) of the Scientific and Technological
Centre CONICET Bahía Blanca (CCTCONICET-BB), in Bahía Blanca, Argentina.
Specimens from the collection of the Facultad
de Ciencias Exactas y Naturales (UNLPam)
were used for taxonomic identification of the
rodent remains.
The MNI (minimum number of
individuals) and MNE (minimum number of
elements) were calculated. The value of
MNI was obtained in two different ways.
Firstly, assessed for each sample, it was
obtained by using different skeletal elements
according to their availability in each pellet.
Secondly, it was calculated using the total
sample in order to compare these data with
other coming from this predator and other
diurnal birds; in this case the calculation
was based on femur remains.
Table 1. Estimated body masses of rodent taxa
present in the studied sample.
Ctenomys sp.
Galea musteloides
Calomys sp.
Reithrodon auritus
* Data from Tiranti (1992)
237
Body mass (g)*
105 - 205
200
9 - 37
74
Taphonomy of the accumulations produced by Caracara plancus
The taphonomic analysis was
undertaken using the methodology proposed
by Andrews (1990) and Fernández Jalvo &
Andrews (1992). This includes 1) an assessment
of the relative abundance of skeletal
elements considering the representation of
each one in the context of the minimum
number of individuals: MNEi/(EixMNI) x100,
where MNEi is the minimum number of
particular skeletal element in the sample and
Ei is the expected number of that skeletal
element in an individual; 2) calculation of
indexes enabled proportion of elements:
(femur + humerus)/(mandible + maxilla); pc/c:
(femur + tibia + humerus + radius + ulna)*8/
(mandible + maxilla + molar)*5 and (tibia + ulna) /
(femur + humerus), and finally the relative
proportion of isolated teeth (incisors and
molars) was calculated with reference to the
number of empty alveolar spaces in mandibles
and maxillae; 3) the evaluation of the degree
of breakage considering the complete remains
separately from the different parts of long
bones (proximal and distal epiphyses, and
diaphyses); and 4) the analysis of degree of
digestive corrosion, mainly that produced
on teeth (incisors and molars), proximal
fragments of femora and distal parts of
humeri.
For the purposes of comparing data
from the skeletal elements of uneaten prey
remains with data obtained from pellets, the
first were analyzed using the same methodology
proposed by Andrews (1990), mainly in terms
of anatomical representation, indexes and
evaluation of the degree of breakage.
Table 2. Number of identified skeletal elements (MNE) in pellets (considering the MNI of 50 and
the MNI of 14) and prey remains, and their relative abundance.
MNE
mandibles
maxillae
incisors
molars
femora
tibias
pelvis
calcaneus
astragalus
humeri
radii
ulnas
scapulas
ribs
vertebrae
metapodials
Average
Pellets
10
7
16
51
17
8
8
8
15
11
7
10
9
20
172
439
Relative
abundance
MNI=50
Pellets
10
7
8
8.5
17
8
8
8
15
11
7
10
9
1.67
9.56
15.68
9.59
Relative
abundance
MNI=14
Pellets
35.71
25
28.57
30.36
60.71
28.57
28.57
28.57
53.57
39.29
25
35.71
32.14
5.95
34.13
55.99
34.24
238
MNE
MNI=35
Prey remains
37
23
1
9
8
6
9
0
0
3
3
3
3
0
0
40
Relative
abundance
MNI=35
Prey remains
52.86
32.86
0.71
2.14
11.43
8.57
12.86
0
0
4.29
4.29
4.29
4.29
0
0
2.04
8.79
Montalvo & Tallade
Pellet sample
Sixty-seven pellets produced by southern
caracara (Caracara plancus) were analyzed.
All of them contained bones of small
vertebrates; 27 of them contained remains of
birds, 1 of a small lizard, and 47 of rodents.
One pellet also contained remains assigned
to an unspecified small felid and another one a
molar fragment of an undetermined Artiodactyla.
The 47 pellets with rodent bones are the
subject of the taphonomic analysis presented
here. Sixteen percent of these pellets
contained a maximum of 10 bone fragments.
The sample included 1,667 remains
(including 171 nails and 10 intervertebral
disks), so we worked on the basis of 1,486 bone
fragments. Of the total remains, 55.58% were
anatomically identified and the rest were nonidentifiable small fragments or bone splinters.
The value of MNI calculated as the
addition of MNI for each pellet rendered a
value of 50. In 34 pellets the recovered materials
could only be assigned to non identifiable
rodents. On the contrary, isolated rodent teeth
and mandibles or maxillae with teeth were
found in 13 pellets, which allowed us to
determine these preys at the level of genus
or species (Table 1). The body mass of the
taxa ranged between 9 and 250 g, but the
largest forms (Galea musteloides and
Ctenomys sp.) were only represented by
juvenile individuals.
All skeletal elements are represented
in the sample and, on the basis of MNI 50; their
relative abundance averages 9.59% (Table 2).
The best represented skeletal elements are
femora, astragali, and metapodials.
On the other hand, in order to compare
the results obtained here with bibliographic
data, the MNI was evaluated on the basis of
the femur in the total sample (MNI=14). In
this case, the relative abundance of skeletal
elements averages 34.24% (Table 2).
The postcranial-cranial proportions
were measured according to two indexes
that showed deficiency in cranial elements
(Table 3), suggesting a further destruction
of these elements. The index that shows the
relationship of proximal and distal elements
had a value of 53.57%, with loss of the
distal limbs. However, it is well known that
the most distal part of the limbs has been better
preserved, as metapodials are abundant. So
it is likely that these elements are better
preserved due to their own characteristics
(size and bone density). The proportion of
isolated teeth, incisors, and molars presented
values in both cases, indicating a very
significant loss of mandibles and maxillae
(Table 3).
The breakage degree of skeletal
elements was very high, except for metapodials,
among which 90% are complete. Groups of
these skeletal elements and 2 or 3 vertebrae
constitute the only remains that have
Table 3. Indexes calculated for the samples.
(femur + tibia + humerus + radius + ulna) / (mandibles + maxilla + molars)*8/5
(femur + humerus) / (mandibles + maxilla)
(tibia + ulna) / (femur + humerus)
% isolated molars
% isolated incisors
239
Pellets
124.71
164.61
53.57
364.29
320.00
Prey remains
53.33
18.33
81.82
128.57
100
Taphonomy of the accumulations produced by Caracara plancus
Table 4. Breakage of postcranial elements in the sample.
Complete
Proximal
Distal
Femur
0
14
3
%
0
82.35
17.65
Humerus
2
5
4
preserved some degree of articulation among
them. No complete femur, tibia, or ulna
were recorded, being the proximal portions
the best preserved, and only two humeri
were complete (Table 4). Particularly, the
cranial elements were broken, the zygomatic
arches not preserved in any specimen; the
bony sutures of the few recovered palates
were open, and there was a very important
tooth loss (Fig. 2 A). There are not complete
mandibles; all of them lack the ascending
ramus, the inferior border is commonly broken,
and none has preserved molars in situ.
The degree of digestion (Table 5)
shows that more than 75% of humeri,
femora, and teeth suffered from moderate to
heavy modifications (Fig. 2 B-J). In all
cases there are specimens with extreme
modifications. In the molars of Galea
musteloides and Ctenomys sp. (Fig. 2 A) the
dentine of the occlusal surface is highly
degraded and cracked. Particularly in cases
of teeth of very young individuals, the
enamel has been removed from the dentine
(Fig. 2 B-C).
%
18.18
45.45
36.36
Tibia
0
8
0
%
0
100
0
Ulna
0
10
0
%
0
100
0
There are a high percentage of non
identifiable bone fragments (44.42% of the
sample). The rounding and polishing of edges
is notable in all remains; thinning, surface
degradation, and presence of holes are also
frequent.
Table 6 offers a summary of the results
obtained through the taphonomic analysis of
the rodent skeletal elements present in the
pellet sample, in which each attribute is
located in a category of modification
according to Andrews (1990), from 1 (little)
to 5 (extreme).
Uneaten prey remains sample
The remains of uneaten preys were
collected for the same period than pellets;
the sample represents 65 individuals of which
39 belong to the rodents Galea musteloides,
Ctenomys sp., and Reithrodon auritus (Fig. 3);
the remaining 26 specimens were portions
of birds and other mammals (Didelphis
albiventris and Felis catus).
Table 5. Assessment of the digestion of postcranial elements and teeth present in
the sample.
% ligth
% moderate
% heavy
% extreme
femur
7.14
42.86
28.57
21.43
humerus
14.29
42.86
28.57
14.29
molar
1.32
53.95
39.47
5.26
incisor
0
50
18.75
31.25
240
Montalvo & Tallade
Figure 2. Degree of digestion in skeletal elements of pellets, A. palate of Ctenomys sp.; B-C. molars of Calomys sp.; D.
molar of Galea musteloides; E-F proximal femora (Rodentia indet.); G. incisor (Rodentia indet.); H-I. distal humeri
(Rodentia indet.); J. incisor (Rodentia indet.).
241
Taphonomy of the accumulations produced by Caracara plancus
Table 6. Categorization of Caracara plancus according to the analyzed variables
(sensu Andrews, 1990).
Category Category Category Category Category
1
2
3
4
5
Postcranial/cranial proportion
Distal elements loss
Breakage of postcrania
Breakage of skull
Loss of zygomatic processes
Maxillary tooth loss
Breakage of mandibles
Mandibular tooth loss
% isolated molars/incisors
Breakage of teeth
Digestion of molars
Digestion of incisors
Digestion of postcrania
The study was based only on the
rodent remains containing skeletal elements
such as head, any portion of the body, and
limbs, always connected by skin with hair
(Fig. 4 A). Four individuals just represented
by skin and hair were excluded. Other
individuals (MNI=35) showed different
skeletal elements that were evaluated using
the same methodology than for the analysis
of pellet remains (Table 2 and Fig. 5). The
relative abundance of skeletal elements
recovered averaged 8.79%. Mandibles,
maxillae, molars, and incisors exceeded 55%
of the representation, whereas none of the
other recovered elements surpassed 13%.
Figure 5 shows the percentages of relative
abundance compared with each element
among the skeletal remains of rodent preys
and pellets; for the latter, MNI was 50.
The indexes evaluated for the sample
of prey remains (Table 3) showed deficiency
in postcranial elements and loss of distal parts
of the limbs. As regards the percentages of
isolated teeth, the values obtained show a
minimal loss of maxillae and mandibles.
The recovered cranial elements showed
a high degree of integrity (Fig. 4 B-E). The
4.44% of the skulls are highly damaged,
being limited to maxillae with teeth and
some sector of the cranial vault, while 20%
consisted of maxillae and rostra with part of
the basicranium. The occipital region was
preserved only in one of the skulls; in most
of them the cranial roof was broken. Two
specimens show semicircular marks, with
highly deteriorated edges in the cranial
vault, which were most probably produced
by the beak. In all cases the zigomatic arches
were broken. About 13% of the mandibles
did not show alterations, 65% of them lacked
only the ascending ramus, and the rest
presented different degrees of modification
242
Montalvo & Tallade
Figure 3. Number of individuals identified as prey remains.
Figure 4. Prey remains. A, B, C, E and F. Galea musteloides; D and G. Ctenomys sp. A.
prey remain; B-E. skulls with different degrees of breakage; F-G. mandibles with different
degrees of breakage. Scale bar: 1 cm.
243
Taphonomy of the accumulations produced by Caracara plancus
Figure 5. Relative abundance of skeletal elements identified in the sample of pellets (MNI=50),
compared with the skeletal elements identified in the sample of prey remains.
Figure 6. Relative abundance of skeletal elements identified in the sample of Caracara plancus
(MNI = 14) compared with data by Andrews (1990) for Falco peregrinus.
244
Montalvo & Tallade
(Fig. 4 F-G). It was common to find complete
mandibles (both halves still articulated) and
only one specimen was articulated to the
skull. Most teeth are found in situ, the
isolated teeth appearing in a low proportion
(less than 2%). Among the postcranial
elements, the more proximal portions of the
limbs were most common, with a higher
representation of pelvis, femora and tibia
over scapula, humerus, radius and ulna, and
in many cases still holding their joints.
No other signs were found, except for
the above mentioned, that could evidence the
activity of scavengers.
Taphonomic analysis of pellets
Based on the remains found in the pellets
produced by a couple of southern caracara
at non reproductive times, it was noted that
microvertebrates (mostly micromammals)
constitute an important part of their diet.
The remains belonging to rodents of less than
500 g body mass were particularly frequent.
Rodríguez Estrella and Rivera Rodríguez
(1997) considered that the southern caracara
preys, whose body mass is less than 500 g,
were captured alive. Moreover, they further
indicated that from the vertebrates found in
the studied samples, more than 60% had
been killed. In this regard, it should be
noted that some remains of larger mammals
were found in the sample of southern
caracara from La Pampa. These remains
certainly were incorporated by carrion
activity of the southern caracara; they are
very fragmentary and show a high degree of
digestion, even in areas of fractures.
Over 70% of the total sample of pellets
contained bones and/or isolated teeth of
rodents. The abundance of rodent remains in
this sample is consistent with data provided
by Vargas et al. (2007). These authors have
indicated this group of mammals as a principal
item in the diet of southern caracara analyzed
in the south of the Buenos Aires Province.
However, it is very important in the whole
sample the presence of non identifiable
fragments and splinters indicating a great
destruction of skeletal elements. In 28% of the
pellets, skeletal remains were identified to the
level of genus or species, and correspond to
rodents Ctenomys sp., Galea musteloides,
Calomys sp. and Reithrodon auritus.
The minimum number of individuals
(MNI) consumed, assessed on the skeletal
elements of each sample, and was 50. In
most samples (94%) there was only skeletal
material from one individual. The relative
abundance of skeletal elements was low,
averaging 9.85%, and the femora were better
represented, but all the elements show a very
low representation. As previously indicated,
if both the MNI and the anatomical
representation are valued using Andrews’
methodology (1990), the MNI evaluated
based on present femora was 14 and the relative
abundance of skeletal elements recovered
averaged 35.17%. In general there are
similarities in the values of the postcranial
elements provided by Andrews (1990) for
some species of diurnal birds. However, the
sample of southern caracara shows a lower
representation of mandibles and maxillae.
For these features the tested sample is
similar to that of Falco peregrinus (Fig. 6).
The analysis of the indexes assessed
for the sample of Caracara plancus showed
that these differ from those given by
Andrews (1990) for diurnal birds, because
in such cases the cranial material was better
represented. One possible explanation for
this difference is that the cranial elements
could be easily destroyed in the digestive
process. All the cranial elements included in
245
Taphonomy of the accumulations produced by Caracara plancus
the southern caracara pellets were highly broken,
which endorses that idea. Proximal elements
of the limbs show a better representation
than the distal ones, but metapodials are
rather well-represented. These latter skeletal
elements are generally complete and some
degree of articulation between them was
found; articulation was also observed among
some vertebrae, mainly the caudal ones. In
general, the rest of the postcranial elements
show high breakage.
All the recovered remains showed a
strong digestive action. Among proximal
femur, distal humerus, molars, and incisors,
values give a high percentage of remains
with moderate to heavy modifications, the
rounded edges of all bone fragments and the
thinning of the walls are also obvious, and
in some cases holes were produced.
Previously, Gómez (2007) examined
a small sample of pellets produced by a
southern caracara in captivity. The material
studied came from an experiment in which
the southern caracara was fed on 32 mice
(Mus musculus) for a week. He obtained
just two pellets, a MNI of 1, and very few
skeletal elements, which indicates the strong
and effective digestive process of these
birds. The sample did not allow him to
conduct a contrastive taphonomic study.
Evidently, the experiment carried out by
Gómez (2007) is interesting but needs a
larger number of pellets, preys, and time of
experimentation to develop a taphonomic
analysis that can be compared with results
obtained under natural conditions as the
ones discussed here.
Taphonomic analysis of uneaten prey remains
The analysis conducted on the remains of
uneaten rodent preys recovered from roosting
shows that 90% of them were analyzable
skeletal remains. Most of the rodent taxa
found in the pellets of southern caracara
(Galea musteloides, Ctenomys sp., and
Reithrodon auritus) were also identified
among the uneaten remains. The most common
prey was Galea musteloides. No remain of
the smallest rodent (Calomys sp.) identified
in the pellets was found, which would
indicate that such preys are full meals. This
suggests that data from the analysis of
consumed preys, on the basis of pellets, is
complemented with the analysis of the prey
remains as suggested for other birds of prey
(Oro & Tella, 1995, Seguin et al., 1998),
and in particular to study the diet of southern
caracara (Rodríguez Estrella & Rivera
Rodriguez, 1997, Travaini et al., 2001,
Morrison & Pias, 2006, Vargas et al., 2007). The
cranial material shows a greater integrity
and representation than the postcranial. The
analysis of the relative abundance of
skeletal elements from prey remains shows
a high representativeness of maxillae and
mandibles. Among the postcranial elements
the representation of femora is slightly
higher than that of the humeri and in both
cases the proximal elements were found
articulated to the pelvic and pectoral girdles,
respectively.
Caracara plancus is not a bird that
decapitates its prey as other raptor birds do
(Andrews, 1990), but at least for the
individuals recovered as prey remains (the
largest among the consumed rodents) these
results suggest that there was a selection of
ingested body parts and that some body
parts are discarded for consumption. The
cranial portions are best represented, showing
a bias to wasting them for consumption. As
already mentioned the relative abundances
of different skeletal elements in the pellets
show a low proportion of maxillae and
246
Montalvo & Tallade
mandibles, and while such a low ratio could
be due to the destruction in the digestive
process of these elements, the alternative of
their absence by pre-selection of other
consumed parts must be considered.
Conclusions
Gómez (2007) suggested that Caracara
plancus is a bird that destroys the remains
of preys or carrion because its digestion is
very strong, but the data presented in this
study only partially supports his results. We
have observed that, in natural conditions,
the consumed remains show moderate to
heavy digestion and, though there is a high
degree of destruction of skeletal elements, it is
possible to retrieve information both taxonomical
and anatomical of the consumed preys on
the basis of the skeletal remains contained
in pellets. This study also shows that even at
low proportions all bone elements of small
preys are represented in the sample.
The observed characteristics justify
the inclusion of Caracara plancus within
the category of heavy modifications.
The comparison of data offered by
pellets and uneaten prey remains indicates
that southern caracara performs a certain
selection over different body parts of predated
rodents, discarding mainly the cranial regions
and to a lesser extent the limbs. Thus, the
skeletal elements, both of the uneaten prey
remains and those contained in pellets, are
exposed in the same area of accumulation.
Over the open plains in central
Argentina, that characterize the area of
collection of pellets and uneaten prey remains,
the pattern of remains accumulation shown
by southern caracara, observed and analyzed
in the present work, could have long-term
consequences. As has been suggested before,
the ingested osseous remains, showing evidence
of breakage and digestion, could accumulate
together with the skeletal elements which
constitute the remains of preys, with particular
signs of breakage but without sign of digestion.
According to the present results, it is
particularly relevant to avoid interpretations
of this kind of accumulations as mixtures
produced by more than one predator, when
actually it is only one with a particular
pattern of ingestion. Consequently, we suggest
that the fact that these birds of prey could have
contributed to the accumulation of
micromammal bones, coming both from pellets
and prey remains, should be taken into account
when zooarchaeological or paleontological
records are analyzed. The record of the
Family Falconidae in the Pampean area goes
back to Late Miocene (Cenizo & Montalvo,
2006); therefore, the obtained results could
help as an analogue for future comparison
of fossil or archaeological accumulations.
Acknowledgments
This work was funded by a Project of the
Facultad de Ciencias Exactas y Naturales,
Universidad Nacional de La Pampa. Special
thanks are given to J. Aguirre for his work
during the meeting and the publication of
this volume. We thank Y. Fernández Jalvo
and L. De Santis for their comments on a first
version of the manuscript. E. Braun and E.
Cerdeño helped with English version. Finally,
G. Gómez and R. Minwer-Barakat provided
insightful comments.
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