Small mammals in the diets of the Long-eared Owl (Asio otus) and Short-eared Owl (A. flammeus) in the south of Western Siberia

Abstract

Diets of the Long-eared and Short-eared Owls, closely related species with overlapping ranges, have been studied in the south of Western Siberia (the Baraba Lowland) by analyzing bone remains in pellets. The results show that both species in the south of the Baraba Lowland employ similar strategies of food resource use, which, however, differ in some aspects. In the Short-eared Owl, the hunting range is apparently more restricted. During the nesting period, these birds occupy relatively moist habitats along riverbanks and protect their hunting grounds. The Long-eared Owl nests in mainly mesic habitats, in forest outliers, and can supplement its diet with shrews (Sorex) and steppe rodent species. The diets of both species largely consist of murine rodent species that are dominant or subdominant in the small mammal community of the Baraba forest-steppe. Seasonal and interannual variations in the food spectra of both species have been revealed.

Full text

ISSN 10674136, Russian Journal of Ecology, 2013, Vol. 44, No. 5, pp. 397–401. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © T.A. Dupal, V.M. Chernyshov, 2013, published in Ekologiya, 2013, No. 5, pp. 356–360.
397
The Longeared Owl (
Asio otus
) and Shorteared
Owl (
A. flammeus
) are two closely related, widespread
species. Their ranges overlap, and they often live in the
same biotopes and often have similar food spectra. In
many areas, both species are exclusively myophagous
and usually prey on the most abundant small rodent
species. Published data on the diets of these birds are
abundant, but different parts of their ranges are char
acterized unevenly (Ekimov, 2003; Sharikov et al.,
2009; Marti, 1976; Birrer, 2009; etc.).
The two species differ in their preferences for nest
ing areas and hunting grounds. The Longeared Owl
prefers hunting grounds in the vicinity of mesic
biotopes with single trees and shrubs and abundant
main prey and occupies the nests of magpies, crows,
and other birds. The Shorteared Owl usually nests on
the ground and prefers moist or overmoistened habi
tats abounding in small mammals (regardless of their
species composition), usually remote from populated
areas. The degrees of stenophagy or euryphagy of the
two species have been discussed in the literature, with
some specialists expressing opposite views on this issue
(Volkov et al., 2009b; Bertolino, Ghiberti, and Per
rone, 2001).
The Longeared Owl is highly selective in its choice
of prey, and if a certain vole species is abundant, the
owl specializes on this particular species (Basova,
2009; Volkov et al., 2009a; Ekimov, 2000a, 2000b;
Golova, 2011; Romanowski and Zmihorski, 2008). In
intrazonal habitats or in cases of population depres
sion in the main rodent species, the Longeared Owl
can considerably expand its food spectrum by utilizing
additional food resources (Danilov, 1976).
The Shorteared Owl shows no particular prefer
ences for prey species, and its food spectrum depends
simply on the abundance of small mammals within its
hunting range (Shepel’, 1997; Clark, 1975; Glue,
1977; Roberts and Bowman, 1986). This range is lim
ited, and the birds protect their hunting grounds, dis
playing specific behavior. Nevertheless, the Long
eared Owl and Shorteared Owl can nest and feed in
the same areas, displaying “dampened” competition
for food resources (Volkov et al., 2009b).
The purpose of this study was to reveal specific fea
tures in the feeding of the Longeared and Shorteared
Owls living in the same area and consuming the same
food resources in the forest–steppe zone of Western
Siberia.
STUDY AREA, MATERIAL, AND METHODS
The material was collected in Zdvinskii raion of
Novosibirsk oblast, in an area adjacent to the south
eastern bank of Malye Chany Lake, from 1976 to 1983.
The Chany area of the Baraba Lowland has a generally
plain topography with alternating low ridges and inter
ridge depressions formed under the action of water
flows, which extend mostly in the northeast–south
west direction. The ridges are usually 3–6 km long and
400–800 m wide. Their height varies but rarely
Small Mammals in the Diets of the Longeared Owl (
Asio otus
)
and Shorteared Owl (
A. flammeus
) in the South of Western Siberia
T. A. Dupal and V. M. Chernyshov
Institute of Systematics and Ecology of Animals, Siberian Branch, Russian Academy of Sciences,
ul. Frunze 11, Novosibirsk, 630091 Russia
email: gf@eco.nsc.ru; chernyshov@ngs.ru
Received June 25, 2012
Abstract
—Diets of the Longeared and Shorteared Owls, closely related species with overlapping ranges,
have been studied in the south of Western Siberia (the Baraba Lowland) by analyzing bone remains in pellets.
The results show that both species in the south of the Baraba Lowland employ similar strategies of food
resource use, which, however, differ in some aspects. In the Shorteared Owl, the hunting range is apparently
more restricted. During the nesting period, these birds occupy relatively moist habitats along riverbanks and
protect their hunting grounds. The Longeared Owl nests in mainly mesic habitats, in forest outliers, and can
supplement its diet with shrews (
Sorex
) and steppe rodent species. The diets of both species largely consist of
murine rodent species that are dominant or subdominant in the small mammal community of the Baraba for
est–steppe. Seasonal and interannual variations in the food spectra of both species have been revealed.
Keywords:
small mammals, Longeared Owl, Shorteared Owl, diet composition, Western Siberia
DOI:
10.1134/S1067413613040048

398
RUSSIAN JOURNAL OF ECOLOGY Vol. 44 No. 5 2013
DUPAL, CHERNYSHOV
reached 15–30 m (Nikolaev, 1978). Numerous lakes,
usually fairly small and shallow, surrounded by exten
sive reed wetlands are the most characteristic land
scape element in the Baraba Lowland. The southern
part of the Baraba forest–steppe is dominated by open
habitats such as meadow steppes, steppificated mead
ows, halophyte assemblages, and other plant forma
tions used as hayfields, pastures, and arable lands. For
ests are represented by small birch and birch–aspen
stands growing in depressions or on ridges (Lapshina,
1978).
The main part of this study was performed on a
ridge in near the mouths of the Kargat and Chulym
rivers, in the vicinity of the Chany Field Station of the
Institute of Systematics and Ecology of Animals. This
ridge forms a large island around 10 km long, with an
area of 5.5 km
2
,where reed grass or couch grass mead
ows 50 to 100 m wide extend along the reed water
meadow, and a small area of herb–grass steppe lies in
the northeast. In the years when the material for this
study was collected, most of the ridge area was used for
growing grain crops, and meadows were usually
mowed. In autumn, horses were corralled there. Tree
vegetation on the ridge is represented by two aspen–
birch ribbon forests totaling 1.8 km in length, 30–50 m
in width, and 6 ha in area.
The seasonal dynamics of the occurrence fre
quency of the owls were studied along a permanent
5km route within a 50m census strip. Over the study
period, the total distance and duration of route cen
suses totaled 875 km and 3400 h. During the nesting
period, six nests of the Longeared Owl and four nests
of the Shorteared Owl were found. In addition, the
results of daily morning and evening censuses of
migrating birds at a permanent station (Gavrilov,
1977) were included in analysis.
The diets of the Longeared Owl and Shorteared
Owl were studied by analyzing bone remains in pellets
collected in the second half of May to early June and
in the second half of August to September near owl
nests or daytime roosts; as a role, only fresh pellets
were collected. The pellets were taken only if the owl
was reliably identified to species. A total of 146 pellets
of the Longeared Owl and 68 pellets of the Short
eared Owl were collected, and 335 and 106 mammal
specimens, respectively, were identified in these pel
lets. From dry pellets, bone remains of prey were
extracted. The remains were identified to species by
cranial characters and the pattern of masticatiory sur
faces of the teeth using corresponding identification
keys (Yudin, 1971; Gromov and Erbaeva, 1995) and
collections of the Zoological Museum of the Institute
of Systematics and Ecology of Animals. Voles of the
genera
Clethrionomys
and
Microtus
were identified
mainly by the morphological characters of the first
lower molar (
М
1
) and the third upper molar (M
3
).
Bone remains were attributed to the same individual if
one pellet contained the remains of the skull and the
right and left lower jaw bones of the same species.
The data were statistically processed in the Statis
tica 6.1 program package. The differences between
prey species frequencies were estimated by twoway
t
test and considered significant at
p
< 0.05.
RESULTS AND DISCUSSION
One or two pairs of Longeared Owls and two or
three pairs of Shorteared Owls nested annually in the
study area. It should be noted that the abundance of
the Shorteared Owl has decreased since the late 1970s
under the impact of predation by badgers (
Meles
meles
) and foxes (
Vulpes vulpes
) and agricultural activ
ities (mowing and plowing up of fallow lands), and
currently this species does not necessarily occur in the
area every year, despite the presence of recently aban
doned fields. During the prenesting and nesting peri
ods, the abundance of owls increased on account of
migrating individuals and emerging young birds. Both
owl species arrived in the first half of April; their high
est abundance was recorded in late April or the first
half of May. Owls of both species were mostly recorded
roosting in the daytime in groves or searching for prey
in the morning or evening. Shortscale migrations of
these owls in the study area begin in late July or early
August, as shown by route and stationary censuses
(Fig. 1).
The diets of the owls did not differ significantly in
the species composition of small mammals and both
included ten rodent species and four shrew species of
the genus
Sorex
(table). No bird remains were
recorded in the pellets of either owl species. The
trophic connections of the Longeared Owl were more
diverse: a total of 14 small mammal species and one
lizard (
Lacerta
sp.) were identified in the pellets. The
food spectrum of this species was dominated by
rodents, especially the root vole (41.8%); the propor
tion of shrews was over 22%. Apparently, if the abun
dance of the main prey species is low, the Longeared
Owl expands its feeding area, which leads to changes
in the number of prey species and their relative pro
portions. The diet composition of the Shorteared
Owl was also dominated by the root vole, which
accounted for almost 60% prey individuals. The pro
portion of shrews in the food spectrum of this species
was considerably lower than in the Longeared Owl
(around 8%), but the proportion of the European
water vole, represented exclusively by small young
individuals, was considerably higher (9.4%).
Comparison of proportions of the main prey spe
cies in the diets of the Longeared and Shorteared
Owls by Student’s
t
test revealed significant differ
ences. The diet of the Shorteared Owl is dominated
(
p
< 0.001) by vole species living near water (the Euro
pean water vole and root vole), while the diet of the
Longeared Owl is enriched by steppe rodent species
(the narrowheaded vole, Eurasian harvest mouse,
and steppe lemming) and insectivores (shrews of the
genus
Sorex
) (
p
< 0.01).

RUSSIAN JOURNAL OF ECOLOGY Vol. 44 No. 5 2013
SMALL MAMMALS IN THE DIETS OF THE LONGEARED OWL 399
Feeding spectra of the Longeared Owl and Shorteared Owl in the south of Western Siberia
Taxon
Longeared Owl Shorteared Owl
number of prey
individuals proportion, % number of prey
individuals proportion, %
Common shrew
Sorex araneus
L. 9 2.7 4 3.8
Tundra shrew
S. tundrensis
Merriam 3 0.9 – –
Laxmann's Shrew
S. caecutiens
Laxm. 3 0.9 – –
Little shrew
S. minutus
L. 2 0.6 – –
Longtailed shrews
Sorex
sp
.
58 17.3 4 3.8
House mouse
Mus musculus
L. 8 2.5 1 0.9
Striped field mouse
Apodemus agrarius
Pall. 6 1.8 1 0.9
Field mice
Apodemus
sp
.
4 1.2 1 0.9
Eurasian harvest mouse
Micromys minutus
Pall. 26 7.6 6 5.7
Siberian hamster
Phodopus sungarus
Pall. 5 1.5 – –
European hamster
Cricetus cricetus
L. 1 0.3 – –
Northern redbacked vole
Clethrionomys rutilus
Pall. 6 1.8 1 0.9
Steppe lemming
Lagurus lagurus
Pall. 17 5.1 4 3.8
European water vole
Arvicola terrestris
L. 10 3.0 10 9.4
Narrowheaded vole
Microtus gregalis
Pall. 37 11.0 11 10.4
Root vole
M. oeconomus
Pall. 140 41.8 63 59.5
Total number of remains 335 100.0 106 100.0
12
0
April
10
8
6
4
2
May
June
July
August
September
October
0.12
0.10
0.08
0.06
0.04
0.02
00
April
8
6
4
2
May
June
July
August
September
October
0.05
0
0.10
0.15
0.20
Ind./km
2
Ind./census Ind./censusInd./km
2
(b)(а)
12
1
2
Fig. 1.
Seasonal dynamics of occurrence frequency (a) of the Longeared Owl and (b) Shorteared Owl according to the results
of (
1
) route censuses and (
2
) stationary censuses.
Analysis of seasonal changes in the food spectrum
of the Longeared Owl has shown that in May–June
the steppe lemming and root vole occur in the diet of
this species significantly more frequently (
p
< 0.0001),
and in August–September the proportion of shrews of
the genus
Sorex
significantly increases (
p
< 0.0001).

400
RUSSIAN JOURNAL OF ECOLOGY Vol. 44 No. 5 2013
DUPAL, CHERNYSHOV
Similar seasonal changes in the proportions of alterna
tive prey species in the food of the Longeared Owl
have also been recorded in other areas of Europe and
Northern Asia (Romanowski and Zmihorski, 2008;
Song et al., 2010). In the case of the Shorteared Owl,
shrews of the genus
Sorex
disappear from the diet in
spring and early summer, while the proportion of root
voles increases significantly (
p
< 0.001); in autumn an
increase in the proportion of European water vole is
observed (
p
< 0.05). Seasonal changes in the composi
tions of small mammal species hunted by owls are
probably explained by the increased migration activity
of rodents during the spring breeding period, which
makes them more vulnerable to predators. European
Water voles live in spring and early summer in reed
wetlands and move onto ridges only by autumn. The
bulk of their population consists of young individuals,
which are the ones that fall prey to owls. The expan
sion of the food niches of both owl species during the
postnesting period is also explained by the lack of
attachment of the birds to particular territories during
this period, which makes them more flexible in their
choice of hunting grounds.
The community of small mammals in the Baraba
Forest–Steppe is known to comprise 21 species. The
dominant assemblage includes the European water
vole, root vole, and field mouse (Glotov et al., 1978).
The highest amplitude of population dynamics is typ
ical of the European water vole. This amplitude in the
root vole and striped field mouse is usually fairly low,
but these species are consistently dominant or sub
dominant among the rodents. The narrowheaded
vole and Eurasian harvest mouse belong to the assem
blage of background species, and their abundance is
relatively low.
Pellets of the Longeared Owl were collected in
1980 to 1983, which allowed us to trace changes in
proportions of dominant and background small mam
mal species over 4 years. Figure 2 shows that the pro
portion of the dominant species, the root vole, in the
diet of this owl considerably changes from year to year.
It can be assumed that 1980 and 1981 were years of a
decline and a rise in root vole abundance, respectively;
1982 was apparently a peak year, and 1983, a decline
year. When the abundance of
M. oeconomus
was rela
tively low, the proportions of shrews and Eurasian har
vest mouse in the owl diet increased; during the second
decline in the abundance of
M. oeconomus
(in 1983),
an increase was observed in the proportions of the
steppe lemming and narrowheaded vole. The propor
tion of root voles in the food spectrum decreased in
years of relatively low abundance of this species but
never dropped below 33%. When the proportion of
rodents living near water decreased, the proportion of
steppe species increased.
Therefore, the two owl species in the study area
show similar strategies of food resource utilization. In
the Shorteared Owl, the hunting range is apparently
more restricted. During the nesting period, these birds
occupy relatively moist habitats along lake shores and
protect their hunting grounds. The Longeared Owl
nests in mainly mesic habitats, in forest outliers, and
1
2
3
5
5
6
100
80
60
40
20
01980 1981 1982 1983
Proportion, %
Fig. 2.
Interannual variation in the diet composition of the Longeared Owl: (
1
)
Sorex
sp.; (
2
)
Micromys minutus
; (
3
)
Lagurus
lagurus
; (
4
)
Arvicola terrestris
; (
5
)
Microtus gregalis
; (
6
)
Microtus oeconomus.

RUSSIAN JOURNAL OF ECOLOGY Vol. 44 No. 5 2013
SMALL MAMMALS IN THE DIETS OF THE LONGEARED OWL 401
can supplement its diet with shrews (
Sorex
) and rodent
species other than those dominating in small mammal
community. In years of relatively low abundance of
root vole, the duet of the Longeared Owl contains
increasing proportions of
Sorex
shrews or the narrow
headed vole and steppe lemming. The tendency
towards stenophagy noted in this species in the Euro
pean part of its range (Basova, 2009; Volkov et al.,
2009a) is not observed in the south of Western Siberia.
Choosing the nesting area, both owl species rely on
evaluation of local environmental conditions, and
both of them show seasonal variations in the food
spectrum. The prevailing murine rodent species in
their diets are those that are dominant or subdomi
nant in the small mammal community of the Baraba
ForestSteppe.
ACKNOWLEDGMENTS
The authors are grateful to K.T. Yurlov, A.K. Yurlov,
V.M. Totunov, A.I. Koshelev, G.I. Khodkov, R.A. Sagitov,
and V.S. Zhukov, who participated in stationary cen
suses.
This study was supported by the Siberian Branch of
the Russian Academy of Sciences, Integration Project
no. 70.
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