Content uploaded by Sergio I. Tiranti
Author content
All content in this area was uploaded by Sergio I. Tiranti on Oct 16, 2014
Content may be subject to copyright.
Available via license: CC BY-NC 4.0
Content may be subject to copyright.
Hystk,
(n.s.) 5(1-2)
(1993):
47-52 (1994)
MAMMAL
PREY
OF
THE BARN
OWL
(TYTO
ALBA)
IN
PARQUE
LURO
RESERVE,
LA
PAMPA, ARGENTINA
SERGIO
I. TIRANTI
CGtedra de Ecologia, Facultad de Ciencias Exactas y Naturales, Universidad Nacioiial de
La
Panipa,
Unigziay
151
and
Miiseo
Provincial de Historia Nahiral, Pelleqrini
180,
6300
Santa Rosa, La Panipa, Aqentina.
ABSTRACT
-
The diet of the barn owl was studied through the analysis of pcllets
obtained in various sitcs within the Parque Luro reserve, located in an area
of
xerophyte CaldCn forests. The study of 1241 prcy items revealed
a
high dominance
of the cricetid rodents
Calomys
sp.,
Akodon molinae
and
Eligmodoritia
typus,
followed by other
8
species of rodents, one species of marsupial and undetermined
birds and anuran amphibians. For comparing the dicts from
a
relatively undisturbed
forested area (Parque
Luro)
and a deforested site, two subcollections of pellets were
analyzed. Differences in FNB values and
in
the prevalence
and
composition of prcy
assemblages were observed between these areas.
Key words: Rodentia, owl pellets, Argcntina.
RIASSUNTO
-
Manmiferi predati dal Barbagiunni
(Tyto alba)
nella Riserva
Purqzie
Liiro,
La
Puiiipu,
Aqeritina
-
La dieta dcl Barbagianni
($to
albu)
6
stata studiata
attraverso l’analisi delle borre ottcnutc in varie localiti all’interno della riserva
Parque Luro, situata in un’area con boschi xerofili a
Prosopis caldenia.
Lo studio di
1241 campioni ha rivelato un’elevata prevalenza di roditori cricetidi
Calomys
sp.,
Akodort nioliriae
and
Elipnodoritia
typus,
seguiti da altre
8
specie di roditori, una
specie di marsupiali
e
uccelli e anfibi anuri indeterminati.
Per
il confront0 delle diete
Sono state analizzate due
sub-raccolte
di borre di rapaci provenienti da un’area
boscata rclativamente indisturbata
e
da un sito disboscato.
In
queste aree
Sono
state
osservatc diffcrcnze nei valori della
FNB
e
nella prevalenza
e
composizione
delle
prede.
Parolc chiavc: Rodcntia,
borre
di barbagianni, Argentina.
I~JTRODUCTION
The cosmopolitan barn owl has a wide distributional range in Argentina.
It is widely known that regurgitated pellets of owls and other birds
of
prey
can be a source of information
on
composition and distribution of small
mammal assemblages (Contoli,
1984).
Parque Luro is a
7607
ha enclosure located
35
km
S
of
Santa Rosa, in
a forested area dominated by the xerophyte Caldkn
(Prosopis caldenia),
but also
having
psammophyte grasslands, halophytic shrublands and
mosaics
of
burned and unburned forests, making up an heterogeneous
habitat. Despite as being the only existing Caldkn forest reserve,
no
published inventory
of
its fauna exists, although it
is
mentioned as a locality
48
Mammal
prey
of
the
Barn
Owl
in the distribution for some animal species (Aravena, 1971) and also a
general description and history has been given
by
Aravena (1972).
Presenty, the Parque Luro is used mainly for harboring a breeding
population of red deer
(Cervus
elaphus)
(Schuerholz, 1983).
Herein, an analysis of prey remains from barn owl regurgitated pellets
is presented.
M
E
T
H
O
D
S
Pellets were collected from
7
different roosting and nesting sites that
were man-made structures in most of the cases, such as warehouses,
abandoned buildings, unused windmill tanks and digouts, and plantations in
the proximity of buildings, from August 1986 to August 1992. Because
collecting was done irregularly and the number of pellets obtained was very
variable, no attempt
was
made to study seasonally or temporally.
All
samples were pooled to conform a total
of
472 pellets which provided 1035
prey remains, also, fragmented pellets and pellet debris yielded
206
individual prey remains, giving
a
total prey number of 1241. The mean
number of prey per pellet was 2.2. The maximum number of prey found in
a single pellet was of 10 individuals, containing 9
Calomys
sp. and 1
Oligoyomys
jlavescens.
As
in an earlier contribution (Tiranti, 1992) identifiable remains, mainly
skulls and skull fragments of mammals and birds, but also amphibian bones
(Di
Palma and Massa, 1981), were recovered from the pellets and
identified to the lowest taxonomical level possible by comparison with
museum specimens. A
few
specimens (N= 15) of small rodents (isolated
maxillae without or with very young or very worn dentition), could not be
determined and were excluded from the analysis.
Food niche breadth (FNB) values were calculated as in Marti (1988).
Biomass was computed using the data presented in an earlier contribution
(Tiranti, 1992).
For analyzing the differences between prey assemblages from a
relatively undisturbed Caldh forest (Parque Luro) and deforested
agricultural land and pastures, a subcollection of pellets was selected from
one site in Parque Luro and another collection of pellets was obtained
from a caliche quarry (Cantera Santa
Rosa)
15
km
N
from the reserve. This
area is characterized by natural pastures and plots for agriculture, existing
also forested patches (road rights of way) nearby. Both subcollections were
of approximately the same date (September 1991) and contained a similar
number of prey items.
Only
Calomys
musculinus
was trapped in Parque Luro (personal
observation) but the presence
of
Calomys
lauchu,
very difficult to
distinguish from remains in pellets, cannot be ruled out.
S.I.
Tiranti
49
Taxonomically problematic species, such as Ctenomys
mendocinus
and
Akodon
molinae
were collected and karyotyped
for
confirmation
of
specific
status.
REULTS
AND
DISCUSSION
As
widely
known,
the barn owl is a rodent specialist predator.
A
recent
review for
La
Pampa province (Tiranti, 1992) showed differences in the
prevalence of
a
particular prey species in barn
owl
diets, that were mostly
dominated by the smaller species
of
cricetid rodents inhabiting the region.
In
Parque Luro, as in other areas of La Pampa and central Argentina,
Calomys
sp. is prevalent, comprising
34.6%
of
the total prey, followed
by
Akodon
molinue
(32.6%),
Eligmodontia
typus
(10.1%)
and smaller
proportions
of
other
8
species
of
rodents, one species of marsupial and
undetermined birds and anurans (Tab.
1).
In
central Argentina the vesper mice
Calomys
musculinus
(Thomas,
1913),
C.
luucha
(Fischer,
1814)
and Azara's grass mouse,
Akodon
azarae
Tab.
1
-
Barn owl prey
derived
from
pellets
collected at Parque
Luro
and comparison
of
prey from pellets between
a
selected
site
from
Parque
Luro
and Cantera Santa Rosa,
September
1991,
La
Pampa, Argentina.
SPEClEs
N
%N
%BIOMASS
P.
LURO
c.
s.
ROSA
FORMAMMALS
N
%N
N
%N
Calomys
sp.
Akodon ntolinue
Elipodoritia opus
Graornys griseoflavus
Akodott uzurae
Oligotyzomys fluvescens
Reithrodori auritus
Cteriontys mendocinus
lliylaniys pusillu
Galea niusteloides
Rathis
sp.
Mus
doniesriciis
Anura
Aves
430
405
125
88
88
26
25
13
12
7
1
1
12
8
Total
1241
FNB
3.4
FNB
for
mammals
3.3
34.60 18.20
32.60 40.70
10.10
5.60
7.10 14.20
7.10 5.20
2.10 1.50
2.00 4.90
1.05
5.30
0.97 0.70
0.60
3.70
0.08 0.20
0.08
0.03
0.10
0.64
155 43.1
71 19.7
78
21.7
20
5.6
11
'
3.1
6.
1.7
6
1.7
1
0.3
7 1.9
1
0.3
47 15.8
1
0.3
212
71.1
6
2.0
5
1.7
5 1.7
11
3.7
3
1.0
7
2.3
4
1.1
1
0.3
360
298
3.47 1.87
50
Mammal
prey
of
the Barn
Owl
(Fischer, 1829), are generally considered Pampean grassland rodents
(Kravetz et al., 1986), Molina’s
grass
mouse,
Akodon molinae
Contreras,
1968 favors areas where more abundant vegetative cover exists, such
as
shrubs and trees (Ojeda, 1989). The silky desert mouse,
Eligmodontia
typus
Cuvier, 1837 has been considered an arid
-
adapted rodent species from the
more arid Monte Desert (Mares, 1977). The rabbit rat
Reithrodon auritus
(Fischer, 1814) is widely distributed generally prefering grassy areas. The
white bellied rat,
Graomys grkeofzavus
(Waterhouse, 1837) is often
associated with forests (can be arboreal) or shrublands, but
also
inhabits
rocky areas. The fossorial tuco tuco,
Ctenomys mendocinus
Philippi, 1869 is
also widely distributed living in clearings of forested areas and
psammophile grasslands.
A
species generally associated with more mesic
conditions is the rice rat
01igoryzomy.s j7avescens
(Waterhouse, 1837)’ which
in some areas of La Pampa, inhabits the semi hallophytic shrublands
of
Cyclolepis genistoides
and
Allenrolfea
spp. in the borders of salt flats and
basins. The mouse opossum
Thylumys pusilla,
is widespread, although not
abundant, and lives in forests and shrublands and can be arboreal. The
yellow toothed cavy,
Galea musteloides
Meyen,
1832
is generally associated
to
shrublands, forested areas and sierras. Some remains of adult specimens
of this species, as revealed by several intact skulls in pellets, are probably
the maximum size that the barn owl is capable
of
handling, having an
approximate weight of 250 g.
The introduced murids
Mus
domesticus
Rutty, 1772 and
Rattus
sp. are of
rare occurrence in barn owl diets in La Pampa, and were obtained in
pellets from highly anthropisized areas within the reserve. The single rat
specimen, a juvenile, represents the first record for La Pampa province as
prey of the barn owl.
The global Parque Luro collection shows the prevalence
of
open area
species
(Culomys
sp.,
Eligmodontia typus),
reflecting the owl’s predatory
habits of using open foraging areas, consuming other species in meagrer
proportions, and having a Food Niche Breadth value of
3.4,
which
is
similar
to the mean of values calculated for La Pampa province (Tiranti, 1992).
For mammals only, the FNB value is 3.3. From the biomass point of view,
Akodon molinae
is
dominant (40.7
%),
followed by
Calomys
sp.
(18.2
%)
and
Graomys griseojlavus
(14.2
%)
(Table 1).
Comparison of the subcollections of September 1991 (Cantera Santa
Rosa and Parque Luro) (Table 1) shows
a
narrower FNB in the more
altered area
of
the quarry (1.87), while in the Parque Luro subcollection a
broader FNB (3.47) denotes a more equilibrated use of food resources.
This
effect
of anthropization has been demonstrated elsewhere (Contoli,
1988; Marti, 1988). The deforestation deprives types of habitats for some
species, such as
Akodon molinae
and
Graornys grkeojlavus,
while it may
S.I.
Tiranti
51
favor the naturally grassland dwellers, which find suitable habitats in
pastures or crops.
The more abundant prey in the quarry were
Elipodontia
&pus
and
Culomys
sp.,
which are open area species.
On
the other hand,
Akodon
molinae
is almost absent. According to Ojeda (1989),
Eligmodontia
@pus
is
an invader
of
altered areas (as fire in the Monte Desert), a fact that may
explain its almost absolute prevalence in the sample
of
the quarry, although
the area studied by Ojeda (1989) is not totally an ecological equivalent to
the areas studied here.
Within the Parque Luro global collection, some differences among sites
were observed, such
as
the presence
of
the
few
Galea musteloides
remains
recovered, that were found only in the proximity
of
the Natural Resources
warehouse, used as roost and nest by a barn owl. In the same area, the
cavies had their burrows and refuges and were easily observable, suggesting
opportunistic predation by the
owls.
Other prey items taken in Parque Luro
were birds, some
of
which could be identifyed:
1
Columbinu
picui
(Columbidae),
3
emberizids similar to
Sicalis luteola,
1
emberizid similar to
Phrygilus carbonarius
and a furnarid similar to
Synalluxis
or
Tripophagu.
ACKNOWLEDGMENIS
-
Park wardens
P.
Borraz and R. Dosio, made
or
assisted in making
the pellet collections, without their invaluable help this research would not have been
possible. Wildlife Deparment authorities P. Steibel and G. Mereb kindly permitted the work
in the reserve.
L.
Contoli is greatly thanked
for
the review and helpful comments on the
first draft
of
the manuscript.
REFERENCES
ARAVENA, R.O.
1971.
Reptiles de La Pampa. Biblioteca Pampeana. Serie Folletos N.
14. 68
PP.
A
RAVENA
, R.O.
1972.
El parque provincial
Los
Caldenes. Acta Zool. Lilloana
29: 141
-
147.
lhcuman, Argentina.
CONTOLI,
L.
1984.
Owl
pellets as an indirect sampling source
for
terrestrial small mammal
populations. Atti
4.
Simposio Dinamica Popolazioni (Parma
22
-
24
Ottobre
1981):
CO~UTOLI,
L.
1988.
Validitl ambientale e diversith trofica: Indice vegetazionali e zoocenotici
a confronto. Braun Blanquetia
2 249-255.
Dr P
ALMA
, M.G.
&
B.
M
ASSA
.
1981.
Contributo metodologico per
10
studio
dell’alimentazione dei rapaci. Atti
I
Convegno Italian0 di Ornitologia, Aulla:
69
-
76.
KRAvm.
F.O.,
R.E.
PERCICH. G.A. ZULETA, M.A. CALLELO
&
M.C. WEISSENBACHER.
1986.
Distribution
of
Junin
virus
and its reservoirs.
A
tool
for
Argentine Hemorrhagic
Fever risk evaluation,
in
non
-
endemic areas. Interciencia
ll(4): 185-188.
M
ARES
,
M.A.
1977.
Water economy and salt balance
in
a South American desert rodent,
Elipnodontia
typus.
Comp. Biochem. Physiol. 56A:
325-332.
M
ARTI
.
C.D.
1988.
A long term study
of
food
-
niche dynamics in the Common Barn
-
Owl:
comparisons within and between populations. Can.
J.
Zool.
66:
1803
-
1812.
O
JEDA
, R.A.
1989.
Small
-
mammal responses to fire in the Monte Desert, Argentina.
J.
Mamm.
70: 416-420.
167
-
176.
52
Mammal prey
of
the Barn Owl
SCHUERHOLZ,
G.
1983.
Informe de consultoria sobre vida silvestre en la provincia de La
Pampa. Agosto-Septiembre
1983.
Proyecto de cooperacibn tkcnica para el desarrollo
regional en cinco provincias argentinas, Repkblica Argentina-Organizacibn
de
Estados
Americanos. Unpublished report.
147
pp.
TIRANTI,
S.
I.
1992.
Barn Owl prey in southern La Pampa, Argentina.
J.
Raptor Res.
26(2):
89
-
92.
Ricevuto il
25
gennaio
1993;
accettato
il
10
settembre
1993
I
Submitted
25
January
1993;
accepted
10
September
1993.
