The Danger of Having All Your Eggs in One Basket—
Winter Crash of the Re-Introduced Przewalski’s Horses in
the Mongolian Gobi
*, Oyunsaikhan Ganbataar
, Nanjid Altansukh
, Namtar Enkhsaikhan
, Chris Walzer
1Research Institute of Wildlife Ecology, University of Veterinary Medicine, Vienna, Austria, 2Great Gobi B Strictly Protected Area Administration, Takhin Tal, Gobi-Altai
Province, Mongolia, 3Department of Zoology, National University of Mongolia, Faculty of Biology, Ulaanbaatar, Mongolia, 4International Takhi Group - Mongolia, Baigal
Ordon, Ulaanbaatar, Mongolia, 5International Takhi Group - Switzerland, Sihlwald, Switzerland
Large mammals re-introduced into harsh and unpredictable environments are vulnerable to stochastic effects, particularly in
times of global climate change. The Mongolian Gobi is home to several rare large ungulates such as re-introduced
Przewalski’s horses (Equus ferus przewalskii) and Asiatic wild asses (Equus hemionus), but also to a millennium-old semi-
nomadic livestock herding culture. The Gobi is prone to large inter-annual environmental fluctuations, but the winter 2009/
2010 was particularly severe. Millions of livestock died and the Przewalski’s horse population in the Gobi crashed. We used
spatially explicit livestock loss statistics, ranger survey data and GPS telemetry to provide insight into the effect of a
catastrophic climate event on the two sympatric wild equid species and the livestock population in light of their different
space use strategies. Herders in and around the Great Gobi B Strictly Protected Area lost on average 67% of their livestock.
Snow depth varied locally, resulting in livestock losses following an east-west gradient. Herders had few possibilities for
evasion, as competition for available winter camps was high. Przewalski’s horses used three different winter ranges, two in
the east and one in the west. Losses averaged 60%, but differed hugely between east and west. Space use of Przewalski’s
horses was extremely conservative, as groups did not attempt to venture beyond their known home ranges. Asiatic wild
asses seemed to have suffered few losses by shifting their range westwards. The catastrophic winter 2009/2010 provided a
textbook example for how vulnerable small and spatially confined populations are in an environment prone to
environmental fluctuations and catastrophes. This highlights the need for disaster planning by local herders, multiple re-
introduction sites with spatially dispersed populations for re-introduced Przewalski’s horses, and a landscape-level approach
beyond protected area boundaries to allow for migratory or nomadic movements in Asiatic wild asses.
Citation: Kaczensky P, Ganbataar O, Altansukh N, Enkhsaikhan N, Stauffer C, et al. (2011) The Danger of Having All Your Eggs in One Basket—Winter Crash of the
Re-Introduced Przewalski’s Horses in the Mongolian Gobi. PLoS ONE 6(12): e28057. doi:10.1371/journal.pone.0028057
Editor: Georges Chapouthier, Universite
´Pierre et Marie Curie, France
Received October 6, 2011; Accepted October 31, 2011; Published December 28, 2011
Copyright: ß2011 Kaczensky et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: No specific funding was obtained for the explicit analyses contained in this manuscript. Rather it is a by-product built on data being collected by a
range of ongoing projects funded by several sources. Main funding was provided by the Austrian Science Foundation FWF project P14992 and P18624 (http://
www.fwf.ac.at/en/index.asp). Additional funding and resources came from the Great Gobi B SPA administration, the International Takhi Group, the University of
Veterinary Sciences in Vienna, and the Mohammed bin Zayed Species Conservation Fund, project no.11251783. The funders had no role in study design, data
collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: email@example.com
Small populations have a high extinction risk due to
demographic stochasticity, the loss of genetic variability, and the
potential detrimental effect of recessive genes . A small
population with a restricted range resembles the proverbial ‘‘all
eggs in a basket’’, as it is particularly susceptible to environmental
stochasticity . However, many re-introduced populations of
large mammals start small  due to logistical and financial
constraints or the controversial nature of the species concerned.
Large mammals re-introduced into harsh and unpredictable
environments are vulnerable to stochastic effects [4,5], particularly
in times of global climate change and the associated increase in
extreme weather events [6,7].
Arid rangelands with a high level of interannual variation in
precipitation are believed to follow non-equilibrium dynamics with
precipitation being the main factor controlling both ungulate and
vegetation dynamics . The Mongolian Gobi in Central Asia
constitutes a vast, largely intact and continuous stretch of non-
equilibrium dry land  which is home to several endangered or
critically endangered large migratory ungulates [10–12] as well as
a millennium-old semi-nomadic livestock herding culture [13,14].
Extreme weather conditions in the form of droughts followed by
cold and snow rich winters (called ‘‘dzud’’ in Mongolia) occur at
irregular intervals and have resulted in mass die-offs of livestock
[15,16]. Although periodic mass winter mortality in wild ungulates
on open range has been documented elsewhere [17–19,11], are
frequently mentioned by local people in Mongolia and acknowl-
edged in the scientific literature (for Asiatic wild asses Equus
hemionus in , Mongolian gazelles Procapra gutturosa in ,
goitered gazelle Gazella subgutturosa in ), the actual impact of
these climatic extremes on wild ungulate population dynamics is
PLoS ONE | www.plosone.org 1 December 2011 | Volume 6 | Issue 12 | e28057
poorly documented, not least because of the difficulties of
obtaining reliable population estimates of wild ungulates over
the vast expanses of the Mongolian rangeland .
Przewalski’s horses have been re-introduced to Mongolia since
1992 and free-ranging populations now exist in Hustai National
Park (NP) in central Mongolia  and in the Great Gobi B
Strictly Protected Area (SPA) in the Dzungarian Gobi in south-
western Mongolia . The initial phase of the re-introduction
programme in the Dzungarian Gobi was plagued with various
problems  and population growth could only be achieved by
introducing additional captive animals. Management changes
were implemented in 1999/2000, but in 2000/2001 the area was
hit by a dzud winter. The population suffered a net loss of 21%
and almost no foals were produced in the spring of 2001 .
Since 2002/03 the Przewalski’s horse population finally started to
show positive population growth, independent of released animals.
The positive population development in the two Mongolian re-
introduction sites has resulted in the down-listing of the
Przewalski’s horse from ‘‘extinct in the wild’’ to ‘‘endangered’’
on the IUCN Red List of Threatened Species . In December
2009 the Hustai NP population had reached 259 animals (D.
Usukhjargal unpubl. data) and the Great Gobi B SPA population
138 animals or almost the ‘‘.140 horses necessary to achieve a
95% probability of survival over 100 years under the low severity
level of catastrophes scenario’’ .
However, in the winter of 2009/2010 one of the worst dzud
conditions ever hit Mongolia. Millions of livestock died, driving
their owners into economic disaster and causing a humanitarian
crisis [28,29]. Concurrently, the Przewalski’s horse population in
the Great Gobi B SPA crashed, providing a textbook example of
the risks faced by small and spatially confined species in
unpredictable environments. By coincidence we also followed
the whereabouts of 10 GPS-collared sympatric Asiatic wild asses
from July 2009 until July 2010. In the following we provide insight
into the effect of a catastrophic climate event on two sympatric
wild equid species and the livestock population of the local semi-
nomadic pastoralists in light of their different space use patterns.
Materials and Methods
All data sets were collected within the frames of the legal
requirements of Austria and Mongolia. Capture and collaring of
Asiatic wild asses was conduced within a cooperation agreement
between the International Takhi Group and the Mongolian
Ministry of Nature, Environment and Tourism signed on
15.02.2001 and renewed on 27.01.2011.
The Dzungarian Gobi in SW Mongolia forms a rather distinct
entity of the Gobi ecosystem due to its geographic location in a
basin surrounded by high mountains and by being located at the
edge of the influence of the Atlantic/Mediterranean and the Asian
Monsoon weather systems . Almost the entire eastern and
central part of the Dzungarian Gobi falls within the 9,000 km
Great Gobi B SPA.
Plains dominate the landscape of the Great Gobi B SPA in the
east and rolling hills in the west. The Altai Mountains flank the
park to the north, and the Takhin Shar Naruu Mountains form
the international border with China (Figure 1A). Elevations range
from 1,000 to 2,840 m. The climate of the Great Gobi B SPA is
continental with long cold winters and short, hot summers.
Average annual rainfall is 96 mm with a peak during summer.
Average snow cover lasts 97 days. Both rain and snowfall can be
highly variable from year to year in space and time.
Desert areas are widely dominated by Chenopodiaceae, such as
Saxaul Haloxylon ammodendron and Anabasis brevifolia. The steppe
areas are dominated by Asteraceae, such as Artemisia and Ajania,
and Poaceae like Stipa and Ptilagrostis . In locations where
several springs occur, these are surrounded by intermittent
swamps and form permanent oases.
The wild ungulate community of the steppe areas consists of
goitered gazelle, Asiatic wild ass, and re-introduced Przewalski’s
horse. Starting in 1992, a total of 89 Przewalski’s horses on 10
transports had been airlifted from abroad to the Takhin Tal
adaptation facilities at the NE edge of the Great Gobi B SPA.
Przewalski’s horses live in stable harems groups, have non-
exclusive home ranges of 152–826 km
, select for the most
productive plant communities and are slow to expand their range
. To speed up range expansion, the last group of re-introduced
Przewalski’s horses, was released at the Takhi us oasis complex,
about 120 km west of the established Przewalski’s horse popula-
tion in 2005 (Figure 1B). In 2007 three wild born stallions were
flown in from Hustai NP to test the feasibility of intra-Mongolian
population exchanges. Wild asses seem to live in fission–fusion
groups, have non-exclusive home ranges of 4,449–6,835 km
show little preference for any particular plant community .
The wild ass population of the Dzungarian Gobi seems to
constitute a distinct subpopulation , numbering several
thousand individuals (P. Kaczensky and R. Ransom unpubl. data).
The Great Gobi B SPA is also used by ,100 semi-nomadic
herder families with ,60,000 livestock. Herders show north-south
seasonal movements between winter pastures along the fringes of
the Dzungarian basin and alpine summer pastures in the Altai
Mountains . Local economy is heavily based on livestock, with
cashmere generating the main income. Since the collapse of the
socialist system local herders have limited access to veterinary care
and largely operate without winter fodder reserves .
We have been recording temperature on an hourly basis using a
data logger (HOBO temperature logger, Hoskin Scientific
Limited, Vancouver, Canada) at Takhin Tal research station
since April 2003. Furthermore, O. Ganbaatar records unusual
weather events in his personal research journal. No further
weather stations are present anywhere in the vicinity of the Great
Gobi B SPA.
To indirectly assess spatial variation in the severity of the 2009/
2010 dzud conditions we obtained spatially explicit livestock loss
data from the majority of local herders in and adjacent to the
Great Gobi B SPA. We obtained information on livestock
numbers and losses by personally interviewing local families
(N = 115) and from livestock statistics collected by the local
(administrative units called ‘‘bag’’) governors (N = 387). We
obtained winter camp coordinates either from 1:100.000 topo-
graphic maps during our interviews or via GPS mapping in the
field. Livestock numbers and losses are largely based on self-
reported numbers by the local herding families.
Przewalski’s horse monitoring
We recorded births and mortalities of individual Przewalski’s
horses based on a horse year lasting from 1 May until 30 April the
following year. Foals born before 1 May were manually assigned to
the correct horse year. Population numbers for each horse year were
calculated as the number of animals alive on 30 April, showing the
Winter Crash of Re-Introduced Przewalski’s Horses
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Figure 1. Impact of the 2009/2010 dzud winter on local nomads and two wild equid species in the Great Gobi B Strictly Protected
Area in south-western Mongolia. A) Livestock loss prediction map as a proxy for winter severity based on the average % total livestock loss at 219
herder camp locations using ordinary kriging, B) Winter losses among the re-introduced Przewalski’s horse population as a function of their
respective winter ranges. The total distribution range in 2009 is based on group locations of 12 harem and 1–3 bachelor groups of Przewalski’s horses
on 129 observation days from January through December 2009. C) Movement patterns of Asiatic wild asses based on GPS positions of 10 wild asses
followed from July 2009 to July 2010 (N = 355,618). Blue dots mark locations during the dzud period (N = 99,220) and red dots locations during the
rest of the monitoring period.
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net gain since the previous horse year. In addition, all births and
mortalities, and in the past transports, were recorded by horse year.
Przewalski’s horse groups were checked by park rangers 1–2
times a week. Rangers were able to individually identify each
Przewalski’s horse based on overall appearance (size, shape, coat
colour, special marks) until the population numbered around 100
animals in 2007. Thereafter, they were still able to identify adult
stallions and all mares, but became increasingly unsure about
Rangers determined the location of individual Przewalski’s
horses and groups based on a raster map, noted group size and
composition, and any peculiarities of individual horses (e.g.
injuries, poor body condition, etc.). An additional 15 Przewalski’s
horses had been followed by satellite telemetry between 2001 and
2008 (for details see [24,33]) and comparison between telemetry
data and ranger monitoring showed that the latter is sufficient to
document the broad patterns of spatial organization of the
different groups and distribution range development (P. Kac-
zensky unpubl. data).
When rangers failed to localize individual Przewalski’s horses
they attempted to locate the horse’s carcass by searching the area
the animal was last seen in. However, during the dzud winter
search efforts were hindered by deep snow and a subsequent snow
melt that transformed large parts of the Gobi into mud flats.
Furthermore, with the ground thawing, wildlife and domestic
animal carcasses at Chonin us quickly started to sink into the many
mud holes. When access finally became possible in April 2010,
rangers walked the area for two full days in search of Przewalski’s
horse carcasses. Rangers collected various tissue samples from all
carcasses encountered for histo-pathological examinations .
Although management of the re-introduced Przewalski’s horse
population has adopted a low intervention policy, emergency hay
was purchased in early March 2010, and the remaining
Przewalski’s horses were supplemented with hay from 7 March–
10 April at Chonin us and from 7–31 March at Takhin Tal and
Takhi us . In addition, several Przewalski’s horses gained
access to old hay reserves at the Takhin Tal camp from November
2009 on and received supplementary fresh hay as early as the
begin of January. However, feeding was frequently disrupted by
heavy snow storms that confined rangers to their homes .
Wild ass monitoring
Between 2002 and 2003 we collared 7 Asiatic wild asses in the
Great Gobi B SPA with Argos and GPS-Argos collars . To
gain more detailed insight into small scale habitat use we captured
an additional 24 asses in July 2007 and July 2009 and equipped
them with GPS store-on-board (SOB) collars that attempted a
GPS fix every 15 minutes over a 12 month period. We retrieved
21 of the 24 collars but due to technical problems only 1 had
monitored ass movements in 2007/2008  while 10 had
monitored wild ass movements during the dzud year 2009/2010
(collecting a total of 355,618 GPS locations, Table S1). All collars
were deployed with drop-off devices (CR-2a, Telonics, Mesa,
USA) programmed to release 12 months after deployment.
We attempted collar retrieval by systematically climbing high
points throughout the Great Gobi B SPA and subsequently
homing in on the signal from the VHF beacon of the shed units.
During our search for shed GPS collars in July 2010 we also
recorded all carcasses of winter-killed wild asses. Furthermore,
rangers made general notes about wild ass carcasses, while
searching for Przewalski’s horses. Carcasses were identified as
potential winter-kills, when they were fresh enough to show
considerable amounts of skin with winter fur and formerly freeze-
dried tissue remains.
For visualization and analysis of spatial data, we used ArcMap
9.3 (ESRI, Environmental Systems Research Institute, Inc.,
Redlands, California, USA). We digitized rivers, springs, oases,
villages and elevations from Russian 1:100 000 topographic maps.
We created a livestock loss prediction map by using ordinary
kriging in the Geostatistical Analyst function. We averaged the
total livestock loss for any given winter camp if more than one
family used the same location. We used the % average livestock
loss of 2010 as the attribute variable to obtain the livestock loss
prediction map, which we subsequently used as a spatially explicit
proxy of winter severity. The proxy map was qualitatively
validated by comparing it to MODIS/Terra satellite snow cover
images  from the onset of the lasting snow cover in November
2009 and from the melt-off phase in March and April 2010 (Figure
For selection of the key variables explaining death or survival of
an individual Przewalski’s horse between December 2009 and
April 2010 we used a generalized additive model (GAM) and a
generalized linear model (GLM) in R  with subsequent least
square model averaging based on Akaike weights of all candidate
models (R library glmulti  and MuMIn). The relative
importance of each variable is expressed as the sum of the AIC
weights from all models that included this variable.
Dzud conditions in the Great Gobi B SPA started on 22
December 2009 and lasted until the end of March. In December
2009 and January 2010 three major snowstorms (22 December, 29
December–7 January and 17–20 January) deposited large amounts
of snow, each packing down the previous layer and in places
reaching accumulated snow depths of 1 m and more. In February
another 5 periods of heavy snow storms occurred, each lasting for
2–3 days. From 6–8 March the last severe snow storm hit, but
temperatures stayed low until mid March (Table S2, Figure S2).
The period from December 2009 until March 2010 was 2.7–5.7uC
colder than during the previous 7 years (Table S2).
Herders in and around the Great Gobi B SPA lost on average
67% of their entire livestock, with only camels less affected
(Table 1). Most affected was the north-eastern part of the Great
Gobi B SPA, where herders lost 80–100% of their livestock. Least
affected were the hills in the central part of the SPA, where
livestock losses were in the magnitude of 20–40%, and the areas in
the west, where losses were in the magnitude of 40–60%
(Figure 1A). The spatial pattern suggests that the weather largely
came from the west and that the snow clouds were stopped by the
high mountains forming the south-eastern tip of the Altai
Mountains thereby depositing the bulk of their snow load at the
north-eastern edge of the Dzungarian basin. This pattern is also
supported by the timing and spatial distribution of the lasting snow
cover in early November 2009 and the thawing pattern at the end
of March/beginning of April 2010 (Figure S1). The majority of
livestock losses occurred during the snow storms in February.
Annual population growth for the horse years 2002/03 until
2008/09 was positive and averaged 12% (range 1–20%; Table 2).
During the horse year 2009/10 the population suffered a net loss of
60%. The main crash happened during the dzud period, with the
population dropping from 138 Przewalski’s horses in December
2009 down to 49 by the end of April 2010. Furthermore only one
foal was born in 2010 (Table 2).
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The main die-off started in January (N = 16), peaked in
February (N = 64) and tailed off in March (N = 6) and April
(N = 3). Winter losses averaged 64% of the early December 2009
population and were most severe in the eastern winter ranges
around Takhin Tal (82%) and Chonin us (73%). However, only
one out of 19 animals (5%) died in the western winter range
around Takhin us (Figure 1B). Most animals seem to have been
lost during snow storms.
Due to the limited vehicle access of large parts of the Gobi from
mid December until the middle of April, rangers could only locate
the carcasses of 33 individuals. However, no living Przewalski’s
horses were reported from anywhere in or around the Great Gobi
B SPA throughout 2010 and 2011, and thus it is safe to assume
that the remaining animals also died.
Area was obviously the key factor for mortality or survival of
Przewalski’s horses during the dzud 2009/2010. In addition, for
the 119 Przewalski’s horses in the eastern winter range, age was
the most likely predictor of mortality, with the youngest age classes
being most affected (Table 3, Figure S3). The influence of sex and
origin of the horses was less certain, but if it played a role, the
effect of a zoo origin (horses born in the Gobi had a higher chance
of survival than those born in a zoo) was twice as strong as the
effect of sex (stallions had a lower survival probability than mares).
Whether or not a mare had a foal in 2009 did not seem to have
any predictive value (Table S3).
Asiatic wild asses
We were able to retrieve 10 out of the 14 collars deployed in
2009. These collars had dropped off the live animals in July 2010,
as they were not associated with a wild ass carcass and the data
showed movements until the drop-off day. We found one collar
with a non-functioning VHF unit by pure chance near a spring,
suggesting that some of the 4 missing units may have had similar
technical troubles. Even with the fate of 4 animals remaining
unknown, a minimum of 71% of our collared asses survived the
dzud winter. Furthermore, rangers did not find any ass carcasses
when searching for deceased Przewalski’s horses at Chonin us and
registered only 1 or 2 wild ass carcasses in the Takhi us winter
range. During 10 days of intensive ground search for dropped
Table 1. Livestock losses in and around Great Gobi B Strictly
Protected Area during the dzud winter 2009/2010 based on
self-reported losses of 502 families.
end Dec. 2009 N lost % lost
Goats 80,797 54,435 0.67
Sheep 59,033 40,068 0.68
Horses 5,211 3,081 0.59
Cows/Yaks 3,377 2,066 0.61
Camels 1,049 258 0.25
Total 149,467 99,908 0.67
Table 2. Population development of the re-introduced Przewalski’s horse population in the Great Gobi B Strictly Protected Area
Horse year Number of Przewalski’s horses Annual l
alive by end of April Born dead Winter
loss trans- ported
1992/93 6 1 0 0 5
1993/94 10 1 5 0 8 21.67
1994/95 9 2 3 0 0 21.10
1995/96 19 2 5 1 13 21.33
1996/97 26 4 5 0 8 21.05
1997/98 26 6 12 4 6 21.23
1998/99 39 5 7 3 15 21.08
1999/00 43 6 6 0 4 1.00
38 15 24 22 4
2001/02 35 140021.08
2002/03 54 13 8 2 14 1.14
2003/04 59 13 8 0 0 1.09
2004/05 86 24 9 5 12 1.25
2005/06 95 22 14 0 0 1.10
2006/07 96 33 32 3 0 1.01
2007/08 113 28 14 2 3 1.15
2008/09 124 36 25 8 0 1.10
49 28 103 89 0
2010/11 48 120021.02
excluding transported horses.
1 December until 15 April, all birth related deaths excluded.
Bold letters indicate horse years with a dzud winter.
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collars in July 2010 we also only came across the carcasses of 2
wild asses from the preceding winter.
The GPS data from the 10 collars revealed that wild asses had
moved west during the dzud period (Figure 1C). This is a pattern
we had not observed in previous years (Figure S4). Three animals
even went well beyond all previous wild ass locations and one
crossed the border fences between Mongolia to China and back
(Figure 1C). The rangers also reported that they had not seen any
wild asses in the eastern part of the park during the winter and that
the very first wild ass did not arrive back in the Chonin us area
until the beginning of April 2010.
Herders and livestock
The dzud winter 2009/2010 was certainly the most extreme
winter in Mongolia during the past 50 years. Fifteen out of
Mongolia’s 21 provinces were declared disaster zones and over 7.8
million livestock, 17% of the national stock, are believed to have
perished . The dzud disaster was caused by the combination of
a very dry summer followed by a long, very cold winter with deep
snow. In many places the situation was aggravated by excessive
livestock stocking rates, reduced mobility and the lack of winter
fodder reserves [16,28].
Due to its geographic location, the eastern part of the
Dzungarian Gobi was particularly heavily hit. In and around the
Great Gobi B SPA stocking rates are moderate, although numbers
were on the rise (from ,60,000 in 2001, see , to ,75,000 by
the end of 2009). While there is little indication for pasture
degeneration so far, there is evidence for competition for good
winter camps (e.g. suboptimal campsites being used, and camps
being burnt down as acts of sabotage), which constitute a key
resource for local herders .
Competition for winter camps allows little spatial flexibility and
when combined with a lack of infrastructure and supporting
services families basically had to stay put, even when the
conditions were bad. Furthermore, during the 2009/2010 dzud
winter deep snow arrived so quickly that people were unable to
move, even if they had an alternative place to go to. Several
families in the eastern part of the Great Gobi B SPA got trapped at
fall camps, which are normally only used for a few weeks after
leaving the summer pastures and before settling into the winter
camps. These families had extended their presence at the
temporary fall camps unusually long because of the rather poor
condition of their winter pastures caused by the preceding
The weather conditions during the dzud 2009/2010 resulted in
the north-eastern part of the Dzungarian basin receiving large
amounts of snow. This area also happened to be the winter range
of the majority of the re-introduced Przewalski’s horses, resulting
in a major population crash. A modelling exercise had previously
identified natural catastrophes as having the greatest influence on
the extinction risk of the small Przewalski’s horse population in
Takhin Tal . However, the frequency, spatial extent and
severity of such unusual weather events are difficult to predict,
making long term model predictions of population growth of small
populations in harsh environments even more unreliable than
under ‘‘normal environmental stochasticity’’ .
Provision of hay after the main die-off may have helped to
reduce late winter mortality at Chonin us and Takhi us, explaining
the slightly lower losses among Przewalski’s horses as compared to
livestock. However, around Takhin Tal access to hay from early
winter on did not prevent massive losses, possibly because feeding
was impossible during snow storms . Consequently, interven-
tion possibilities for free-ranging animals during natural disasters
of the magnitude of the 2009/2010 dzud seem very limited.
On the regional scale the damage to Przewalski’s horse recovery
in Mongolia was somewhat dampened by the fact that the winter
range of the third Przewalski’s group in the Great Gobi B SPA was
located in an area less affected by the dzud, and on a national scale
by the fact that winter losses at Hustai NP were much lower and
only amounted to 10% of the early December population (D.
Usukhjargal unpubl. data). Close cooperation between the two re-
introduction sites already resulted in a transport of horses from
Hustai NP to the Great Gobi B SPA and negotiations for further
transports to speed up population recovery are ongoing.
Furthermore, there are plans to transport Przewalski’s horses
from a breeding facility in adjacent China to Mongolia.
As during the dzud 2000/2001, the youngest age classes
suffered the highest mortality . What came as a surprise
though was that zoo born Przewalski’s horses, despite having lived
in the Gobi for multiple years, may still have a lower survival
probability than those born in the Gobi. It also appears that mares
may be less susceptible to succumbing to dzud conditions than
stallions. Histo-pathological examination of samples collected from
33 Przewalski’s horse carcasses did not suggest that disease played
a major role in the dzud 2009/2010 die-off (A. Ku¨bber-Heiss,
unpubl. data), as had been the case during the dzud 2000/2001
. Our findings suggest that with the increasing proportion of
Gobi born Przewalski’s horses the re-introduced population may
become more robust in facing future dzud conditions, although we
have yet to understand the underlying adaptive mechanisms.
Although, contrary to livestock, Przewalski’s horses were not
constrained to any particular place by the choice of a herder, they
nevertheless stayed put in the area most affected by the dzud.
Access to hay from early winter on may have been a reason for the
17 Przewalski’s horses around Takhin Tal to remain. However,
the 102 horses at Chonin us did not receive hay until after the
main die-off had already happened. The area most heavily
impacted included the horses’ winter and summer range. The re-
introduced Przewalski’s horses seem very conservative in their
range use, having comparatively small home ranges, clear habitat
preferences, and showing only a slow tendency for range
expansion . Przewalski’s horse groups in the north-eastern
part of the SPA overlap and interact, but there seems to be no
contact to the group at Takhi us (O. Ganbaatar unpubl. data).
Consequently, the re-introduced population still has a rather
limited spatial knowledge, and venturing beyond the known range
during extreme conditions would be somewhat of a risky strategy.
Table 3. Averaged model parameters of a general additive
model (GAM) for survival or mortality of 119 Przewalski’s
horses that wintered in the eastern part of the Great Gobi B
Strictly Protected Area during the dzud winter 2009/2010.
Coefficient z value
Intercept 20.669 0.413 0.652
na na 0.062
Sex_Stallion 20.855 0.472 0.070 0.68
Origin_Zoo 21.763 0.994 0.076 0.61
See Figure S3 for relationship.
Pvalue based on the full model including all 3 variables.
Winter Crash of Re-Introduced Przewalski’s Horses
PLoS ONE | www.plosone.org 6 December 2011 | Volume 6 | Issue 12 | e28057
Whether autochthonous Przewalski’s horses were more mobile
than the present-day re-introduced animals is unknown. From
other species we know that sedentary and migratory animals or
subpopulations can coexist within the same species and habitat
. Thus it is possible that during captive breeding either the
behavioural tradition or the genetic component for exploratory
movements was lost. However, the severe effect of this localized
catastrophic event was largely due to the small size and limited
range of the present day Przewalski’s population. A large and
continuous population would be able to counteract local
population lows or extinctions via re-colonization.
Asiatic wild asses
Although we have no means of quantifying the impact of the
dzud 2009/2010 on the Asiatic wild ass population, evidence
suggests that mortality was low. GPS tracking data and ranger
observations show that wild asses moved away from the most
severely affected areas in the north-eastern part of the Dzungarian
Gobi, a pattern we had not observed in previous years [12,24],
(also see Figure S4). Contrary to sympatric Przewalski’s horses,
wild asses have large home ranges, show little dependence on a
particular habitat type and seem to live in fission-fusion groups
. Due to the different scale of habitat use, winter severity
within the asses’ home range was patchy, rather than uniform as
was the case within the much smaller Przewalski’s horse home
ranges, or punctual like for the fixed winter camps of local herders
and their livestock. The lack of a distinct spatial substructure
within the wild ass population  likely facilitates information
transfer between individuals and subgroups  and may allow
individuals access to information well beyond their individual
home range , making exploratory long distance movements
during extreme conditions less risky.
The dzud winter 2009/2010 is a text book example for how
vulnerable small and spatially confined populations are in an
environment prone to fluctuations and catastrophes. Losses of this
magnitude are difficult to predict or model in any reasonable
framework and will in any case remain probabilities. As long as
populations remain small and spatially confined, success is not
guaranteed, necessitating a long term conservation commitment.
The difference in how severely the Przewalski’s horse popula-
tion was affected, on a local as well as a national scale, highlights
the advantage of distributing your ‘‘eggs in more than one basket’’.
Consequently, the national strategy for Przewalski’s horse
conservation in Mongolia should continue to aim for multiple
re-introduction sites with spatially dispersed populations and close
cooperation among projects on a national as well as an
Wild asses were obviously able to avoid the worst of the dzud
winter by moving west, up to 50 km beyond the Great Gobi B SPA
boundary. These long distance movements and range shifts highlight
again how vulnerable migratory or nomadic ungulates are to
fragmentation and how important it is to manage them on a
landscape-level, including multi-use areas outside of protected areas.
The spatial flexibility of local herders is restricted by the limited
availability of suitable winter camps and further complicated by
administrative boundaries and a lack of cooperation beyond the
extended family. Consequently, outrunning a dzud disaster is
hardly an option and people will need to prepare for dzud events
by means of banking during good years, improved husbandry and
control of stocking rates and diversification of their means of
income. Certainly, the herding sector will not be able to provide a
livelihood for a growing population in the future.
Figure S1 Snow cover dynamics from the first snowfalls
in November 2009 to snow melt in April 2010, over-
imposed with high loss areas from the % livestock loss
prediction map. Generally, high loss areas correspond with
areas that received snow early and where snow stayed long. Snow
depth can be indirectly inferred from snow melt patterns.
Quantitative analyses were hindered by 1) the inability to remotely
measure snow depth, and 2) the high percentage of satellite images
with total or partial cloud cover (e.g. images top left & images in
the middle), resulting in large no-data zones.
Figure S2 Snow conditions in and around Takhin Tal in
February and March 2010.
Figure S3 Probability of mortality for the 119 Przewals-
ki’s horses that wintered in the east part of the Great
Gobi B SPA during the dzud winter 2009/10 based on
age. The solid line shows the value predicted by the general
additive model (GAM) based on a spline with 8 knots. The dashed
lines are the 95% credibility intervals.
Figure S4 GPS positions of 8 wild asses between July
2002 and July 2009, years with no dzud winters. No
avoidance of the eastern part of the park, as in 2009/10, is seen.
For detailed description of data collection and monitoring period
see  and .
Table S1 GPS data from 10 Asiatic wild asses moni-
tored from July 2009 until July 2010.
Table S2 Temperatures based on hourly measurements
at Takhin Tal research station at the NE edge of the
Great Gobi B SPA in SW Mongolia. A) Average monthly
temperatures from April 2003 through August 2010. B) Daily
mean temperature from November 2009 through April 2010.
Table S3 Averaged model parameters of a general
linear model (GLM) for survival or mortality of 39 adult
Przewalski’s horse mares (age
4 years) that wintered in
the eastern part of the Great Gobi B SPA during the dzud
This work would not have been possible without the dedicated work of the
local rangers under the worst possible conditions. We are grateful to Felix
Knauer who helped with the statistical analysis, Henrik von Wehrden who
helped with acquiring the MODIS/Terra satellite snow cover images, John
Linnell who provided comments and corrections on an earlier version of
this manuscript and Karin Svadlenak-Gomez who helped with the final
editing. This work is dedicated to the brave people in and around the Great
Gobi B SPA who suffered so much hardship during the dzud winter 2009/
Analyzed the data: PK. Wrote the paper: PK. Collection of field data: PK
OG NA NE. Capture and collaring of animals: CW PK OG NE. Winter
monitoring of study site 2009/2010: OG NA NE. Manuscript correction
and comments: CW CS.
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