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ARCTIC
VOL. 69, NO. 2 (J UNE 2016) P. 121 – 129
http://dx.doi.org/10.14430/arctic4559
Emergent Rainy Winter Warm Spells May Promote Boreal Predator
Expansion into the Arctic
Aleksandr A. Sokolov,1,2,3 Natalya A. Sokolova,1,2 Rolf A. Ims,4 Ludovic Brucker5,6 and Dorothee Ehrich3,4
(Received 28 May 2015; accepted in revised form 9 November 2015)
ABSTRACT. Climate change has been characterized as the most serious threat to Arctic biodiversity. In addition to gradual
changes such as climate warming, extreme weather events, such as melting temperatures in winter and rain on snow, can
have profound consequences for ecosystems. Rain-on-snow events lead to the formation of ice layers in the snow pack, which
can restrict access to forage plants and cause crashes of herbivore populations. These direct impacts can have cascading
effects on other ecosystem components, often mediated by trophic interactions. Here we document how heavy rain in early
winter, leading to the formation of a thick layer of ice, was associated with dramatic mortality of domestic reindeer on Yamal
Peninsula, Russia. In the subsequent summer, breeding of two boreal generalist predators, red fox and Hooded Crow, was
recorded for the rst time in a monitoring area in the Low Arctic tundra of this region. We suggest that the resource pulse
created by the abnormally high reindeer mortality and abundance of carrion may have facilitated these breeding events north
of the known breeding range of the two species. Our observations provide an example of how specic emergent weather events
may indirectly pave the way for more abrupt, although possibly temporary, species range changes.
Key words: Arctic fox (Vulpes lagopus); red fox (Vulpes vulpes), Hooded Crow (Corvus cornix); domestic reindeer; ground
icing; rain on snow; food web; range expansion
RÉSUMÉ. Le changement climatique a été caractérisé comme la plus grande menace à la biodiversité de l’Arctique. En
plus des changements graduels comme le réchauffement climatique, les phénomènes météorologiques extrêmes comme les
températures positives en hiver et la pluie tombant sur la neige peuvent avoir de profondes conséquences sur les écosystèmes.
La pluie tombant sur la neige mène à la formation de couches de glace dans le manteau neigeux, ce qui peut avoir pour effet
de restreindre l’accès aux plantes fourragères et d’entraîner l’effondrement des populations herbivores. Ces impacts directs
peuvent avoir des effets en cascade sur d’autres composantes des écosystèmes, et cette propagation passe souvent par des
interactions trophiques. Dans cette communication, nous décrivons comment une pluie abondante en début d’hiver, menant à
la formation d’une couche de glace épaisse, a été accompagnée par une mortalité dramatique des rennes domestiques dans la
péninsule de Yamal, en Russie. L’été suivant, la reproduction de deux prédateurs boréaux généralistes, soit celui du renard roux
et celui de la corneille mantelée, a été enregistrée pour la première fois dans une aire d’étude de la toundra du Bas-Arctique
de cette région. Nous suggérons que l’abondance de ressources créée par le taux de mortalité anormalement élevé de rennes
et l’abondance de charognes aurait pu susciter ces épisodes de reproduction au nord de l’aire de répartition connue des deux
espèces. Nos observations fournissent un exemple selon lequel des phénomènes météorologiques émergents particuliers
peuvent, indirectement, ouvrir la voie à des changements plus abrupts en matière d’aire de répartition des espèces, bien que ces
changements puissent être temporaires.
Mots clés : renard arctique (Vulpes lagopus); renard roux (Vulpes vulpes), corneille mantelée (Corvus cornix); renne
domestique; englacement du sol; pluie tombant sur la neige; réseau alimentaire; agrandissement de l’aire de répartition
Traduit pour la revue Arctic par Nicole Giguère.
РЕЗЮМЕ. В настоящее время, изменения климата представляются наиболее серьезной угрозой для биоразнообразия
Арктики. В дополнение к постепенным изменениям, таким как потепление климата, экстремальные погодные
явления (зимние потепления до температуры таяния или жидкие осадки на снежный покров) могут иметь
серьезные последствия для экосистем. Погодный феномен «дождь-на-снег» приводит к формированию слоев льда в
снежном покрове, что может ограничивать доступ к кормовым растениям, и явиться причиной падения популяций
1 Arctic Research Station of Institute of Plant and Animal Ecology, Ural Branch, Russian Academy of Sciences, Labytnangi, Russia
2 Science Center for Arctic Studies, State Organization of Yamal-Nenets Autonomous District, Salekhard, Russia
3 Corresponding authors: sokhol@yandex.ru and dorothee.ehrich@uit.no
4 University of Tromsø – The Arctic University of Norway, Department of Arctic and Marine Biology, Tromsø, Norway
5 NASA Goddard Space Flight Center, Cryospheric Sciences Laboratory, Code 615, Greenbelt, Maryland 20771, USA
6 Universities Space Research Association, GESTAR, Columbia, Maryland 21046, USA
© The Arctic Institute of North America
122 • A.A. SOKOLOV et al.
травоядных. Подобные прямые воздействия могут привести к каскадным эффектам на другие компоненты экосистем,
часто через трофические взаимодействия. В настоящем сообщении мы документируем, как сильные дожди в начале
зимы привели к формированию толстого слоя льда, что, по всей видимости, явилось причиной катастрофической
смертности домашних северных оленей на полуострове Ямал в России. В следующее лето на мониторинговой
площадке в кустарниковой тундре Ямала впервые было зарегистрировано размножение двух хищников-генералистов
из бореальной зоны – обыкновенной лисы и серой вороны. Мы предполагаем, что ресурсный импульс, обеспеченный
аномально высокой смертностью оленей и, как следствие, обилием падали, мог способствовать появлению случаев
размножения этих двух видов к северу от известной границы их распространения. Наши наблюдения являются
примером того, как возникающие экстремальные погодные явления могут опосредованно проложить путь к более
резким, хотя вероятно и временным, изменениям ареала видов.
Ключевые слова: песец (Vulp es lagopus); лиса (Vulpes vulpes), серая ворона (Corvus cornix); домашний северный олень;
ледяная корка; дождь-на-снег; трофическая сеть; увеличение ареала
INTRODUCTION
Climate change is more rapid in the Arctic than in other
areas of the world and has been characterized as the most
serious threat to Arctic biodiversity (Meltofte et al., 2013).
Many of the documented trends of change in terrestrial
ecosystems, such as northwards range shifts of boreal spe-
cies, increase in the growth of shrubs or changes in carbon
budget are responses to gradual changes in climate, such as
rising temperature or earlier snowmelt (Ims et al., 2013a).
In addition to such trend effects, extreme weather events,
which are predicted to increase in frequency and mag-
nitude, can have profound consequences for ecosystems
(Jentsch et al., 2007; Bokhorst et al., 2008; Hansen et al.,
2014). Such events can accelerate shifts in species compo-
sition and distribution (Wernberg et al., 2013) and induce
transitions between ecosystem states that are not always
easily reversible (Mueller et al., 2005; Jentsch et al., 2007).
In addition to direct impacts on climate-sensitive species or
processes, both trend effects and consequences of extreme
weather events can have cascading effects on other ecosys-
tem components, effects that are often mediated by trophic
interactions (Post et al., 2009; Ims et al., 2013a).
A consequence of a warmer and wetter climate is an
increase in the frequency of periods of melting tempera-
tures during winter and of rain-on-snow events in some
regions of the Arctic (AMAP, 2011). These events can
have catastrophic consequences for plant and animal pop-
ulations. Refreezing after rain or melting periods in win-
ter leads to the formation of ice layers in the snow pack or
on the ground surface. This ice prevents herbivores from
accessing their food, which can cause heavy mortality in
populations of large herbivores such as reindeer (Rangi-
fer tarandus; Aanes et al., 2000; Miller and Gunn, 2003),
and may become a major problem for reindeer husbandry
(Moen, 2008). Rain-on-snow events have been rare in most
of the Arctic (Rennert et al., 2009). In the oceanic climate of
High Arctic Svalbard, however, winter rain has been a nor-
mal (but stochastic) feature of the weather pattern for dec-
ades, although recent events appear to have become more
important than before (Hansen et al., 2014). These events
in Svalbard cause synchronized crash-recovery dynam-
ics within the entire winter-resident vertebrate community
(Hansen et al., 2013). Weather-induced winter mortality of
reindeer and other herbivores appears to be the key ingredi-
ent of these dynamics.
Ungulate carcasses can be a valuable food resource for
carnivores in northern winters (Wilmers et al., 2003). Stud-
ies of Arctic foxes (Vulpes lagopus) in Svalbard have shown
that more foxes were breeding in inland dens after winters
with high reindeer mortality and thus good access to food
from carcasses (Fuglei et al., 2003; Eide et al., 2012). In
Subarctic and Low Arctic Norway, higher densities of resi-
dent semi-domestic reindeer provide more potential carrion
in winter, leading to a strong increase in the presence of all
carnivore species, but particularly of typical boreal forest
mesopredators such as red foxes (Vulpes vulpes), Hooded
Crow (Corvus cornix), or eagles (Aquila chrysaetos and
Haliaetus albicilla; Henden et al., 2014). In the same region,
diet analyses revealed that reindeer carrion was a key
resource for red foxes during winters with low lemming
(Lemmus lemmus) abundance in the tundra (Killengreen et
al., 2011).
The expansion of widespread generalist predators into
the Arctic tundra is one of the ongoing trends in changes
affecting terrestrial Arctic ecosystems (Ims et al., 2013a).
Subarctic generalists such as red fox or Hooded Crow can
have a negative impact on native Arctic species. For exam-
ple, interspecic competition with the larger red fox is one
of the major causes for the decline of the endangered Arc-
tic fox in northern Fennoscandia (Tannerfeldt et al., 2002;
Angerbjörn et al., 2013). Moreover, red foxes and corvids
are important nest predators (Ims et al., 2013b) and have
been hypothesized to contribute to the decline of Willow
Ptarmigan (Lagopus lagopus; Henden et al., 2011; Ehrich et
al., 2012) and Lesser White-fronted Geese (Anser erythro-
pus; Norwegian Directorate for Nature Management, 2011)
in the same region.
Henden et al. (2014) suggest that increased access to rein-
deer carrion in late winter may allow forest-dwelling mam-
malian mesopredators and corvids to establish and breed in
tundra. Anthropogenic subsidies from deliberate feeding
or waste are known to enhance breeding both in red foxes
(Angerbjorn et al., 1995; Stickney et al., 2014) and in ravens
(Corvus corax) (Newton et al., 1982). However, we are not
aware of studies that have directly linked the establishment
PREDATOR EXPANSION INTO THE ARCTIC • 123
of boreal predators in Low Arctic tundra to specic weather
events. Here we document how a pulse of resources caused
by exceptional mortality of domestic reindeer after a rain-
on-snow event was followed by the rst records of breeding
by boreal generalist predators in Low Arctic Yamal, Russia.
Our observations contribute to the growing understanding
of how important emergent extreme weather events are in
driving ecosystem change and highlight the role of subsidies
in modifying the composition of the tundra predator guild.
MATERIAL AND METHODS
Study Area
The study was carried out at the Erkuta Tundra
Monitoring Site in the southern part of Yamal Peninsula,
Russia (68.2˚ N, 69.2˚ E; Fig. 1). This Low Arctic area
(bioclimatic zone E; Walker et al., 2005) is characterized
by a gently rolling tundra landscape with low hills (ca.
30 m high), including some steep slopes and sandy cliffs
along riverbanks and lakes (Sokolov et al., 2012). Mean
temperature in the area is −24.1˚C in January and 11.4˚C
in July, and mean annual precipitation is about 335 mm
(averages for the period 1950 – 2000; downloaded from www.
worldclim.org). A stable snow cover is usually established in
October and lasts until early June. Rain-on-snow events are
typically rare in the western Siberian Arctic (Groisman et
al., 2003; AMAP, 2011). For southern Yamal, the study by
Groisman et al. (2003) reports an average frequency of
0 such events per winter in the period 1950 – 2000 (Noviy
Port weather station). The vegetation has been classied
mostly as low shrub tundra, with erect dwarf shrub tundra
in drier places (Walker et al., 2005; Magomedova et al.,
2006). The area is situated ca. 150 km north of the southern
border of the tundra area as dened by the circum-Arctic
vegetation map (Fig. 1; Walker et al., 2005). Forest also
extends northwards into the tundra area along the valley of a
larger river (Shuch’ya), and the northernmost forest patches
are found ca. 110 km south of our study area. Numerous
water bodies create extensive wetlands, and dense thickets
of willows and in some places alders occur along rivers and
lakes.
The small rodent community is dominated by two spe-
cies of Microtus voles (M. middendorfi and M. gregalis)
and has during the last decade exhibited multi-annual uc-
tuations of rather low amplitude (Sokolova et al., 2014).
Forty-one species of birds, including numerous waterfowl,
passerines and waders, are breeding in the area (Sokolov et
al., 2012). The medium-sized herbivores, Willow Ptarmigan
and mountain hare (Lepus timidus), are relatively abundant
(Ehrich et al., 2012). The Yamal Peninsula is a traditional
Nenets reindeer-herding region. Reindeer numbers have
increased over the last decades (Klokov, 2012) to more
than 300 000 on the peninsula at present. Our study area is
used by reindeer herds in all seasons. Some of these herds
migrate over long distances, and others are more local.
The most common mammalian predator is the Arctic
fox, but least weasel (Mustela nivalis), stoat (M. erminea),
wolverine (Gulo gulo), and wolf (Canis lupus) are also pre-
sent. Red foxes are rare, but they are sometimes observed
in winter and have been shot (three times to our knowl-
edge) by Nenets people living in the study area in the years
2007 – 13. Since 2008, single red foxes have been registered
in some years on automatic cameras with baits in late win-
ter (A.A. Sokolov, unpubl. data). In summer, only a few
observations of red foxes have been recorded, although the
species is unusual for the area and thus conspicuous, which
implies that observations would certainly have been written
down. A red fox pup was observed in 1989 on the banks of
the Erkuta River (V.G. Shtro, pers. comm. 2015). Annual
monitoring of small rodents and birds was initiated in the
area in 1998. Since then red foxes have been observed in
only two summers. Two individuals were recorded in
2007. One of them intruded on an Arctic fox den, leading
to the abandonment of the den by the Arctic fox family
(Rodnikova et al., 2011). In 2013 a single individual was
observed close to a den at the periphery of the study area.
Red foxes are regularly breeding in the forested Shuch’ya
valley (S.A. Mechnikova, pers. comm. 2015), ca. 110 km
south of our study area.
The most common birds of prey in the area are Rough-
legged Buzzards (Buteo lagopus), Peregrine Falcons (Falco
peregrinus), and Long-tailed and Arctic Skuas (Stercorarius
longicaudus and S. parasiticus). Ravens have been breed-
ing in the study area since 2009. They were able to establish
themselves after the construction of a railroad bridge across
the Erkuta River in 2008. Hooded Crows have been recorded
in late spring or summer, but no signs of reproduction have
been observed. Breeding of Hooded Crows north of forested
areas on Yamal has previously been observed only around
settlements (Golovatin and Sokolov, 2009).
Data Collection
The extreme weather event with heavy rain in Novem-
ber 2013 was documented by direct observations, the rec-
ollections of local people, and data from weather stations.
In addition, we used information from satellite microwave
sensors to determine the extent of the area affected. Passive
(radiometer) or active (scatterometer) satellite microwave
sensors allow the identication of regions that experi-
enced icing conditions resulting from rain-on-snow events
or melt-and-refreeze cycles (e.g., Grenfell and Putkonen,
2008; Bartsch et al., 2010). The algorithm used here is
based on satellite observations from the Advanced Micro-
wave Scanning Radiometer 2 (AMSR2) obtained at fre-
quencies of 18.7, 36.5, and 89 GHz (L. Brucker, A. Ivanoff,
and N. Maynard, unpubl. data). The algorithm includes a
combination of temporal and spectral detection of rain-on-
snow events. AMSR2 satellite observations were obtained
from the JAXA GCOM-W1 Data Providing Service
(https://gcom-w1.jaxa.jp/). The remote sensing data were
validated with data from 10 official weather stations
124 • A.A. SOKOLOV et al.
(obtained from www.rp5.ru) and one additional station in
the Polar Urals (V. Ivanov and V. Mazepa, pers. comm.
2015).
Estimates of the number of dead reindeer were obtained
from ofcial sources (Government of Yamalo-Nenetskiy
Autonomous District) and supplemented by qualitative
information from local residents.
Since 1998, the abundance of small rodents and their
main predators has been monitored in the study area,
though with varying intensity. Birds of prey have been
studied since 1999 (Sokolov, 2003) and the whole bird
community was surveyed in detail in the period 2002 – 09
(Sokolov et al., 2012). Systematic Arctic fox den surveys
have been carried out each summer since 2007. This sur-
vey began with a core area of ca 130 km2 that comprised
most breeding dens known at that time (Rodnikova et al.,
2011). In subsequent years, the study area was progressively
enlarged, and new dens were described. In 2014, the area
covered 230 km2 and comprised 21 dens in which breeding
had occurred at least once since 2007, as well as 22 other
dens with four entrances or more (Fig. 2). All known dens
were checked annually for signs of fox activity and breed-
ing. Since 2009, active dens have been monitored with auto-
matic cameras to determine the number of pups.
1
9
8
7
6
5
4
3
211
10
A
B
C
D
E
Yenisey
Ob'
Pechora
Ya
Pr Na Pu
Ta
Kr
Shu
0 250 500 km
FIG. 1. Map of the Yamalo-Nenetskiy Autonomous District in Northwest Siberia (Russia) with Yamal Peninsula in the center. The ve bioclimatic subzones
of the Arctic (A – E; Walker et al., 2005) are shown in various shades of green. The seven districts (Ya – Yamalskiy, Ta – Tazovskiy, Shu – Shuryshkarskiy,
Pr – Priuralskiy, Na – Nadymskiy, Pu – Purovskiy and Kr – Krasnoselkupskiy) are outlined in green. The blue spot in southern Yamalskiy District represents
the study area. Black shading shows areas where surface freezing after the rain-on-snow event was inferred from satellite microwave sensor data. Numbered
circles represent weather stations (1 – Polar Ural, 2 – Salekhard, 3 – Noviy Port, 4 – Maresale, 5 – Seyakha, 6 – Antipayuta, 7 – Nyda, 8 – Yangi Yugan,
9 – Muzhi, 10 – Nadym, 11 – Noviy Urengoy). Red circles indicate stations that registered rain on 8 – 9 November 2013, and white circles show stations that
did not record rain.
PREDATOR EXPANSION INTO THE ARCTIC • 125
RESULTS
Icing Event
According to resident Nenets people, a rather deep
snow cover was established in the study area on 23 Sep-
tember 2013—about three weeks earlier than usual—dur-
ing a three-day snowstorm. On 8 and 9 November, heavy
rain fell on the snow-covered ground and led to the forma-
tion of a solid ice layer over large parts of the tundra. Posi-
tive temperatures and rain were registered at Noviy Port
weather station, which is the closest weather station to our
study area (Fig. 3). From the satellite data, ground icing due
to the rain-on-snow event was inferred for a large area that
encompassed our study area and covered the whole south-
ern part of Yamal Peninsula, as well as parts of the Nadym-
skiy, Purovskiy, and Tazovskiy districts farther east (Fig. 1).
The spatial extent of the rain-on-snow event was conrmed
by available data from weather stations. Rain was recorded
in the area that experienced icing, but not in northern Yamal
or in areas farther south (Fig. 1). After that rst event, more
rain fell in December, forming a solid ice layer at the bot-
tom of the snow pack. This event was registered as sleet in
Noviy Port (Fig. 3). This weather station is situated 165 km
east of the study area on the eastern coast of Yamal, so it is
likely to experience slightly different weather. The ice layer
did not melt until spring, blocking access to the eld-layer
vegetation for several months. The thickness of the ice layer
was not measured.
Reindeer Mortality
We visited the study area several times between January
and April 2014, and every time, herders told us that many
of their reindeer had died and that the situation was very
difcult. According to ofcial data, 40 000 reindeer died
in Yamalskiy district (in which our study area is situated)
and 15 500 in the adjacent Priuralskiy district. No statistics
were available about reindeer mortality in winters without
icing. Herders estimated, however, that in winter 2013 – 14
FIG. 2. Map of the study area at Erkuta in southern Yamal. Red stars show the two dens occupied by red foxes in 2014, and pale blue stars show active Arctic fox
dens in 2014. Filled black circles represent Arctic fox dens where breeding has been observed since 2007, and open circles show dens where no breeding was
observed. The Gazprom railroad Obskaya-Bovanenkovo crosses the area.
126 • A.A. SOKOLOV et al.
reindeer mortality was about 10 times higher than usual.
When working in the study area in summer, we found
numerous reindeer carcasses.
Generalist Predator Reproduction
During the period 2007 to 2013, we found on aver-
age 4.4 dens (range: 0 – 8) with reproducing Arctic foxes
in the study area, which corresponds to 2.6 ± 1.9 dens per
100 km2. No reproduction by red foxes was observed, but a
single red fox was observed on a den in 2007 (Rodnikova
et al., 2011). In 2014, we registered seven dens occupied by
Arctic fox families and discovered two dens with red fox
pups. The dens where red fox were breeding were situated
in the core of the study area (Fig. 2). On 18 June 2014, four
pups were observed playing on den 10, a rather old den situ-
ated close to a lake, where Arctic foxes had not reproduced
since 1999. An adult with unusual black and yellowish coat
color approached, barked, and ran away. Later in the day,
we went back to the den to inspect it and set up an auto-
matic camera. The den showed clear signs of activity: a lot
of feces, trampled vegetation, and remains of feathers and
sh. The pictures from the automatic camera revealed six
red fox pups, two dark morphs and four typical red morphs.
No adult was recorded, and the last picture of a pup was
taken on 19 June at 23:55. After that, no fox activity was
recorded on the den, indicating that the pups were moved.
The other red fox breeding was recorded on 21 June in
den 11, situated on a small peninsula created by a sharp
turn of the river (Fig. 2), a den where Arctic foxes had been
breeding in 2007. We noticed activity when observing the
den from the river, at a distance of 300 m. We saw three red
fox pups, clearly identied by their body shape, relatively
big ears, and red fur. Later in the day we returned to the den
to inspect it and set up an automatic camera. On that visit,
we saw six pups playing on the den. The pictures from the
automatic camera conrmed the number of pups. Unlike the
foxes in den 10, those on this den did not move after the dis-
turbance, and the last picture of a pup was taken on 3 July.
The rst nest of a Hooded Crow ever recorded in the study
site was found on 24 June. The nest was built about 2 m
above ground on a willow shrub ca 4 m high. There were
three chicks in the nest, and two adults were alarm calling.
On 3 August, we observed a dark red fox pup on the
bank of the Erkuta River, which suggested that at least
some of the dark pups from den 10 had survived. In win-
ter 2014 – 15, the local Nenets people shot ve red foxes in
the study area, compared to only three in total in the period
2008 – 14.
DISCUSSION
Our observations from southern Yamal in 2013 – 14 sug-
gest that an extreme climatic event, in this case strong rain
falling on snow and frozen ground in November, likely
induced abnormally high reindeer mortality and thus a
large pulse of resources for scavenging carnivores. We sug-
gest that this reindeer die-off was the proximate factor that
facilitated the rst recorded breeding of two boreal gener-
alist predators/scavengers in the Low Arctic tundra of the
Yamal Peninsula and mediated the indirect effect of an
extreme weather event (i.e., melting temperatures and rain
in winter) on predators by increasing a food resource (i.e.,
reindeer carrion). Reindeer mortality during winter and the
availability of reindeer carrion has indeed been shown to be
related to Arctic fox den occupancy on Svalbard (Fuglei et
al., 2003; Eide et al., 2012). Eide et al. (2012) suggest also
that litter size in Arctic foxes is determined by resource
abundance in winter. For red foxes, supplementary feeding
at dens in northern Finland during late winter and spring
enhanced breeding (Kaikusalo and Angerbjörn, 1995).
In northern Norway, both the proportion of pregnant vix-
ens and the proportion of juveniles in the population were
-40-30 -20-10
01
0
Daily mean temperature C
020406080
Snow depth in cm
1 Sep1 Oct1 Nov1 Dec1 Jan1 Feb1 Mar1 Apr
o
FIG. 3. Weather recorded at Noviy Port weather station in winter 2013 – 14. The black line traces mean daily temperature, whereas the red dotted line indicates
0ºC. The vertical blue bars indicate days when precipitation was recorded (higher dark blue bars for rain, and lower light blue bars for sleet). Light blue shading
indicates snow; however, since snow depth was not recorded in Noviy Port, it shows depth registered at the Salekhard weather station (situated farther south in
the region; see Fig. 1).
PREDATOR EXPANSION INTO THE ARCTIC • 127
correlated with resource availability during winter (Killen-
green et al., 2013). Red foxes are mobile opportunistic feed-
ers that roam into tundra areas. We suggest that because
they encountered abundant resources—many carcasses
were rather intact in spring, and reindeer of the weakened
herds died also in spring and summer—they may have set-
tled down to breed. The same may have been the case for
Hooded Crows, which previously had been observed in our
study area only as single birds, but bred in 2014 given the
unusually good resource basis. This species is also known
to be an opportunistic feeder and takes advantage of car-
casses (Killengreen et al., 2012).
The suggested causal relationships linking the icing
event, reindeer mortality, access to carrion, and presence
of generalist predators in a new area are further supported
by studies from southern Yamal in 2006 – 07. Indeed in
that winter unusual successive icing events occurred on
southern Yamal starting in November (Forbes et al., 2009;
Bartsch et al., 2010). As in 2013 – 14, the ice blocked the
access to pastures for domestic reindeer and resulted in
important losses of animals (Forbes et al., 2009). In sum-
mer 2007, two red foxes were recorded in our study area,
one of which intruded on an Arctic fox den leading to aban-
donment of the den (Rodnikova et al., 2011). Moreover, the
highest breeding activity of Arctic foxes was recorded in
the study area in that year (8 out of 12 known breeding dens
were active, resulting in six Arctic fox pairs per 100 km2).
Although red fox breeding was not documented in 2007, it
may have occurred outside of the surveyed area.
The importance of additional resources or subsidies
for the expansion and establishment of red foxes in tun-
dra areas has long been recognized. Hersteinsson and
Macdonald (1992) suggested that red foxes could benet
from an increase in primary and secondary productivity
induced by climate warming. Some support for this hypoth-
esis has been obtained in northeastern Norway, where red
foxes seem to have replaced Arctic foxes in the most produc-
tive denning habitat (Killengreen et al., 2007). In other areas
of the Arctic, however, red and Arctic fox populations have
been stable over several decades despite pronounced climate
warming (Gallant et al., 2012), which indicates that increased
primary production did not necessarily favor red foxes. Other
evidence suggests that resource subsidies in winter, which
are often provided by human activity, have played a decisive
role for the growth of red fox populations in tundra areas in
northern Fennoscandia (Kaikusalo and Angerbjörn, 1995;
Killengreen et al., 2011) and Alaska (Savory et al., 2014;
Stickney et al., 2014). Although little is known about the
expansion of corvids into the Arctic, anthropogenic resources
appear to be important as well (Restani et al., 2001). Thus
our observations are in agreement with the general pattern of
subsidies favoring generalists. However, whereas the studies
mentioned above address gradual changes in resource levels,
we documented the way in which a weather-induced pulse
of resources allowed at least a temporary range expansion of
boreal/subarctic predators.
At present, extreme weather events in the Arctic occur
in addition to ongoing trends of change such as climate
warming and changes in land use. In southern Yamal, the
abundance of semi-domestic reindeer has indeed increased
considerably over the last decades (Klokov, 2012). Together
with the rapid development of extractive industries in the
region, the high numbers of animals may make the herds
particularly vulnerable (Forbes et al., 2009; Golovatin et
al., 2012). As rain-on-snow events are predicted to increase
in frequency in the Arctic with ongoing climate change
(Rennert et al., 2009), reindeer herders will have to adapt
to a more frequent risk of winter icing, and future man-
agement options may be determinant for the expansion of
boreal generalist predators. A combination of trend effects
with stepwise changes due to specic events and modulated
by management decisions is likely to be typical for global
change – induced ecosystem changes (Jentsch et al., 2007).
Only future observations will show whether, after this
rst breeding record, red foxes and Hooded Crows will
manage to establish in Erkuta, leading to a permanent range
expansion, or whether they will not be able to breed there
after winters with low reindeer mortality. The future avail-
ability of reindeer carrion will depend on the frequency of
winter icing and on herd management with respect to icing
risk. The abundance of alternative prey, such as hare or
waterfowl, may also play a role, but it is difcult to make
any predictions about their future population changes. A
possible lasting change in the composition of the predator
guild with more boreal generalists is likely to have a det-
rimental impact on many typical Arctic species, in par-
ticular ground-nesting birds, such as ptarmigan or waders,
and Arctic foxes (McKinnon et al., 2010; Angerbjörn et al.,
2013; Ims et al., 2013b).
ACKNOWLEDGEMENTS
We thank the Laptander family for their support throughout
this study, and Maite Cerezo, Nikolay Erokhin, Ivan Fufachev,
Tatyana Strukova, and Sergey Zykov for help and company
in the field. This study has been partly supported by the
programs of Ural Branch of the Russian Academy of Sciences
12-4-7-022-Arctic and 15-15-4-35-Arctic, and by the Norwegian
Environment Agency. The Inter-regional Expedition Centre
“Arctic” contributed funding and logistical support.
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