Biological Conservation 144 (2011) 2787–2798

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Biological Conservation
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Review

Conservation consequences of Chernobyl and other nuclear accidents
A.P. Møller a,⇑, T.A. Mousseau babLaboratoire d’Ecologie, Systématique et Evolution, CNRS UMR 8079, Université Paris-Sud, Bâtiment 362, F-91405 Orsay Cedex, France
Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USAa r t i c l e

i n f oArticle history:
Received 16 May 2011
Received in revised form 22 August 2011
Accepted 25 August 2011
Available online 19 October 2011
Keywords:
Mutation
Mutational load
Radiation
Radioactivity
Selective mortalitya b s t r a c t
The explosion at the Chernobyl nuclear power plant on 26 April 1986 released vast amounts of radioactive material over an area of 200,000 km2 in eastern and central Europe, affecting all living organisms. The
biological impacts including the conservation consequences of this event are still poorly known even
25 years after the disaster. Here we assess the effects of this environmental disaster for conservation
by focusing on two connected questions addressing the short-term ecological and the long-term evolutionary consequences: First, we pose the question of whether rare species are more impacted by radiation
than common species? Second, what are the conservation consequences of elevated mutation rates dueto the mutagenic effects of radionuclides from Chernobyl? Furthermore, we assess the extent to which
ecological and evolutionary aspects interact. We censused breeding birds across 731 census points in
Ukraine and Belarus during 3 years to assess the relationship between abundance of different species
and radiation. Most bird species avoided contaminated sites and individuals were concentrated in relatively uncontaminated sites. While common species were recorded at a wide range of radiation levels,rare species were restricted to the least contaminated sites and to sites with a high biodiversity. Thus,
rare species were disproportionately impacted by the accident. Mutation rates of plants and animals haveincreased by up to a factor 20 due to release of radionuclides from Chernobyl. Given that each slightly
deleterious mutation is expected to result in a selective genetic death, and that an average fruitﬂy undernormal conditions may carry as many as 80 mutations, the number of mutations in animals and plants
around Chernobyl and hence the number of selective deaths is bound to be much higher. There is empirical evidence for highly elevated mortality rates and dramatically increased rates of reproductive failure
in contaminated areas, consistent with the expected high frequency of selective deaths due to mutations.
The average slightly deleterious mutation is present for 33–167 generations in Drosophila, so if theseestimates are qualitatively similar in other organisms, we can expect that mutants will disperse outsidecontaminated areas resulting in the spread of mutations well beyond the reach of contamination withradionuclides. Therefore, it should be possible to document the gradual spread of mutations from
Chernobyl. We consider that the Chernobyl disaster and other nuclear releases may have signiﬁcant consequences for population size and population viability of many species due to the large number of selective deaths. These effects remain to be investigated. Finally, comparative analyses of birds revealed thatspecies with high mitochondrial DNA substitution rates had short dispersal distances, suggesting that
mutations will spread relatively short distances when they are common, but will spread longer distancesin species when they are rare.
Ó 2011 Elsevier Ltd. All rights reserved.

Contents
1.
2.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2788
Material and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2789
2.1.
Study sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2789
2.2.
Confounding variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2789
2.2.1.
Plumage coloration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2790
2.2.2.
Migration distance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2790
2.2.3.
Dispersal distance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2790

⇑ Corresponding author. Tel.: +33 1 69 15 56 88; fax: +33 1 69 15 56 96.
E-mail address: anders.moller@u-psud.fr (A.P. Møller).
0006-3207/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biocon.2011.08.009

2788

3.

4.

A.P. Møller, T.A. Mousseau / Biological Conservation 144 (2011) 2787–2798

2.2.4.
Egg mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2791
2.2.5.
Habitat generalism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2791
2.2.6.
Body mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2791
2.3.
Mitochondrial DNA substitution rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2791
2.4.
Measuring background radiation levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2791
2.5.
Comparative analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2791
2.6.
Statistical analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2792
Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2792
3.1.
Are rare species particularly susceptible to radioactive contamination?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2792
3.2.
Mutational load and radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2793
Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2795
4.1.
Radiation and rarity in birds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2795
4.2.
Mutation rates and mutational load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2795
4.3.
Future repercussions of the Chernobyl disaster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2796
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2796
Appendix A.
Supplementary material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2796
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2797

1. Introduction
Chernobyl is singularly the largest environmental disaster ever,affecting millions of people (Møller and Mousseau, 2006; Yablokov
et al., 2009). Reported estimates suggest fallout equivalent to thatfrom 100 to 400 atomic bombs of the size dropped on Hiroshima
and Nagasaki in 1945, with widespread distribution of contaminants
across an area about 200,000 km2 in eastern and central Europe(Yablokov et al., 2009). Additional cases of radioactive contamination have also been reported from the former Soviet Union, UK,
USA and most recently the Fukushima region of Japan. In addition,
vast areas of the world were contaminated with radioactive fallout
stemming from widespread nuclear bomb testing (e.g. Miller,
2002). Furthermore, nuclear power plants habitually emit radioactive gases and liquids by design to the environment under theassumption that this is quickly diluted and hence has little or no signiﬁcance for humans or free-living organisms (NRC, 2011). Finally,natural levels of background radiation from radionuclides vary bymore than two orders of magnitude across the globe with areas withvery high levels of natural radioactivity being present in China, India,
Iran, Kenya, Namibia, France, Brazil and many other places (GhiassiNejad et al., 2002). Such radiation may occur as radioactive particles
in rock or in the form of gases like radon that then can be trapped inside buildings and increase human exposure to mutagens that cause
cancer (e.g. Lubin and Boice, 1997; Hendry et al., 2009). Given that
additional nuclear accidents seem inevitable, and that all nuclear
facilities emit some level of radioactive efﬂuent, there is good reason
to address questions related to the conservation consequences ofsuch leakage of radioactive material into the environment.
The biological consequences of radiation from the Chernobyl
catastrophe are poorly known because to date rather limited research has been conducted (Zakharov and Krysanov, 1996; Møller
and Mousseau, 2006; Yablokov et al., 2009). The general area affected by fall-out from Chernobyl had a background radiation levelof only 0.02–0.04 lSv/h, which is among the lowest in the world(Ramzaev et al., 2006). Thus radiation is bound to disproportionately affect local populations due to lack of local adaptation to radiation. Previous studies at Chernobyl have revealed severely
reduced species richness, abundance, and population densities ofbirds in the most contaminated areas (Møller and Mousseau,
2007a,b). Species richness of birds was reduced by 60%, whileabundance was reduced by 70% across the more than four ordersof magnitude difference in radiation levels that can be found within the exclusion zone (Møller and Mousseau, 2007a,b). Similar, oreven more extreme relationships, have been recorded for bumblebees, butterﬂies, grasshoppers, dragonﬂies and spiders (Møller andMousseau, 2011). Birds can actively avoid contaminated areas asshown for pied ﬂycatchers Ficedula hypoleuca and great tits Parus
major when offered a choice between nest boxes in more or lesscontaminated areas (Møller and Mousseau, 2007c). This suggeststhat biodiversity in general may be severely depressed in contaminated areas around Chernobyl, despite the fact that the most recent review of the biological consequences of the Chernobyl
disaster suggested that the Chernobyl Exclusion Zone was a wellfunctioning ecosystem with increasing numbers of rare species(Chernobyl Forum, 2005a,b; UN Chernobyl Forum Expert Group‘‘Environment’’, 2005). However, we note that this assessment
was not based on published, quantitative data, and thus we consider this claim to be unsubstantiated until empirical evidence
proves otherwise.
The conservation consequences of radiation from the Chernobyl
accident or any other nuclear accident have never been addressed
explicitly or implicitly in the literature. Thus, there is no empiricalor theoretical basis for making a review of this question. Obviously,
this does not imply that there are no conservation implications,only that these have so far not yet been studied. Here we suggestthat two complementary effects of radioactive contamination occur, short-term ecological effects of radiation that may affect rare
species disproportionately, and long-term evolutionary effects
due to accumulation of mutations even beyond the immediate areaof contamination. These two effects may also show signiﬁcantinteractions because ecological conditions may have synergistic effects at the evolutionary level. For example, mutations may haverelatively greater effects on rare than on common species if selective deaths due to mutation affect rare species disproportionately.
Likewise, slightly deleterious mutations may migrate outside theareas that are contaminated with dispersing individuals. If species
that suffer from high rates of mutation caused by radiation also
have high dispersal propensity, such species will suffer disproportionately from migration of mutations outside the contaminatedareas. The converse would be the case if such species had relatively
short dispersal distances.
Are rare species disproportionately affected by radiation? Rarity
could be due to a lack of suitable habitat, a lack of dispersal ability,
or a lack of phenotypic characteristics that allow species to reachhigh population densities. Habitat generalism is an important feature of the ability of different species to exploit available habitats,with specialists having a narrow niche and generalists a broad
niche (e.g. Futyuma and Moreno, 1988; Julliard et al., 2006). Specialists are likely to have smaller population sizes than generalists
because they can only successfully exploit a narrow range of habitats. Hence, habitat specialization may constitute an important as-

A.P. Møller, T.A. Mousseau / Biological Conservation 144 (2011) 2787–2798

pect of what makes some species rare. Dispersal may affect local
abundance and hence the presence of rare species if rare species
are particularly susceptible to the effects of dispersal for maintenance of local populations. Dispersal is a mechanism by which local species diversity can increase due to a greater number of
immigrants (e.g. Planty-Tabacchi et al., 1996; Levine and D’Antonio, 1999; Stohlgren et al., 1999; Levine, 2000). Furthermore,
long-distance dispersal plays an important role in invasions (Shaw,
1995; Koenig et al., 1996), and some studies have suggested thattaxa with longer dispersal distances have larger range sizes (e.g.
Edwards and Westoby, 1996; Kelly, 1996). Here we analyzed local
patterns of biodiversity in a bird community to investigate effects
of dispersal propensity on local species richness and the presenceof rare species. Thus we pose the question: What are the effectsof radioactive contamination from Chernobyl on species that varyin abundance, from locally rare to very abundant species? Are rare
species more impacted? Are species with higher threat status more
impacted?
There are species-speciﬁc differences in impact of radiation onabundance (Møller and Mousseau, 2007b), historical mutation
rates (Møller et al., 2010), and current mutation rates (Baer et al.,2007). There are also interspeciﬁc differences in the prevalenceof phenotypic abnormalities in birds living in areas around Chernobyl (Møller et al., 2007). Given that historical mutation rates asreﬂected by mitochondrial DNA substitution rates are positively
correlated with the extent of the negative effect of radiation onabundance of different species of birds (Møller et al., 2010), thisindicates that particular species are consistently susceptible tothe effects of mutagens across evolutionary time scales.
Mutagenic effects of radiation were ﬁrst identiﬁed by Nadson
and Philippov (1925) for fungi in the 1920s and developed further
by Muller (1950). Thus, we should expect the mutational load toincrease in areas contaminated with radioactivity. Indeed estimates of mutation rates from the surroundings of Chernobyl suggest that these are increased by up to a factor twenty compared toestimates from uncontaminated control areas (Ellegren et al.,
1997; Møller et al., 2005b; review in Møller and Mousseau,
2006). The germline mutation rate is usually much higher in males
than in females, especially in older males due to the larger numberof germ-cell divisions. Previous studies of DNA substitutions suggest that the rate of deleterious mutation may be sufﬁciently highto affect disease frequency in humans, and by inference in otherorganisms as well (Crow, 1997, 2000). The rate of minor deleterious mutations in Drosophila fruitﬂies is on the order of one mutation per zygote (Mukai, 1964), but a much greater number of genes
in vertebrates including humans suggests that these effects will bemuch greater in the latter taxa (Crow, 1997). The mutational costin terms of ﬁtness was inferred by Muller (1950) to equal one ‘‘genetic death’’. However, selective deaths usually remove multiple
mutations thereby reducing the mutational load (Muller, 1950).
The effects of mutational leakage from contaminated to uncontaminated areas around Chernobyl are poorly understood. For
example, if species with high mutation rates had low dispersal
rates, this could reduce the spread of mutations to uncontaminated areas for such species, while an elevated dispersal ratewould have the opposite effect. Thus, the effects of dispersal on
migration of mutations will partly determine the extent to which
different species are affected by mutations beyond the areas ofcontamination. We will brieﬂy review the arguments addressingthese questions.
Although there is no literature addressing the conservation consequences of radiation from Chernobyl or any other nuclear accident, we believe that an assessment of this question is both
timely and needed. We use our own extensive data from Chernobyl
collected since 1991 to address these important conservation questions. The objectives of this study were to review the impact of

2789

radiation from Chernobyl on conservation by investigating theshort-term ecological and the long-term evolutionary effects of
the Chernobyl accident. Because there is no literature dealing
explicitly or implicitly with this subject, we present original research on the relationship between radioactive contamination
and abundance. We do so, ﬁrst, by testing if rare species are disproportionately affected by contamination from Chernobyl. Second,
we review the literature on mutational load due to slightly deleterious mutations from a theoretical point of view. Again, there is noliterature addressing this question so we review the genetics literature addressing mutational effects in order to arrive at a qualitative assessment of the potential effects. After having reviewed therelationship between mutational load and selective deaths due tomutations, we make an explicit empirical test of whether the frequency of mutations is related to dispersal propensity becausesuch a relationship will affect the rate at which mutations will travel beyond the immediate area that is contaminated and hence thesize of the population that is affected by radiation. Speciﬁcally, we
test if species that are particularly susceptible to the effects of radiation as reﬂected by high mitochondrial substitution rates differ indispersal distance from species with low rates because such differences will affect the rate of spread of slightly deleterious mutations
beyond the contaminated areas, but also determine which species
will be the most affected by mutational load. Because mutation
rates in the male germline generally exceed those in the female
germline (Crow, 1997; Bartosch-Härlid et al., 2003), we evaluate
the consequence of such sex-bias for mutational load. This sexbiased mutation effect is exacerbated by a sex difference in mortality in contaminated areas with a preponderance of male-biased
tertiary sex ratios.

2. Material and methods
2.1. Study sites
APM conducted standard point counts during late May – early
June 2006–2008 (a total of 731 counts), with each count lasting
5 min during which all birds seen or heard were recorded andidentiﬁed to species (Møller, 1983; Bibby et al., 2005; Møller andMousseau, 2007a, 2009b; Voříšek et al., 2010). Points were locatedat a distance of at least 75 m intervals within forested areas around
Chernobyl (Fig. 1). The point counts were made across a range ofradiation levels spanning over four orders of magnitude (Fig. 1;
Møller and Mousseau, 2007a, 2009a,b). Information on weather(temperature, precipitation, cloud cover, wind), habitats (coverwith herbs, shrub, trees, presence of water, type of soil) and date
and time of day were recorded at each census point (review in
Møller and Mousseau, 2011).
We used abundance of different species of breeding birds
summed across all census points as a measure of total abundance.
We considered species that were recorded with 1–5 individuals to
be rare, and used the number of such species at each census point
as an estimate of rare species. The ﬁndings reported here did not
rely on this speciﬁc threshold value because analyses using an
upper threshold from 3 to 10 individuals provided qualitatively
similar conclusions (results not shown). Thus we only report results for species recorded with 1–5 individuals.

2.2. Confounding variables
We included the following variables in the models because they
have previously been shown to predict effects of radiation on theabundance of birds in the neighborhood of Chernobyl (Møller
and Mousseau, 2007b).

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A.P. Møller, T.A. Mousseau / Biological Conservation 144 (2011) 2787–2798

Fig. 1. Study sites (blue dots) used for censusing birds in the area around Chernobyl and level of background radiation (darker colors imply higher levels of radiation).
Modiﬁed from European Union (1998). (For interpretation of the references to colors in this ﬁgure legend, the reader is referred to the web version of this paper.)2.2.1. Plumage coloration
We have previously shown that carotenoid- and pheomelaninbased plumage coloration predicts susceptibility to radiation,
apparently because radiation results in depletion of antioxidants,
and carotenoids and precursors of pheomelanin play importantroles as antioxidants (Møller and Mousseau, 2007b; Galván
et al., 2011). We scored the breeding plumage of all species as
sexually monochromatic if males and females did not differ incoloration according to information provided by the descriptions
in Cramp and Perrins (1977–1994), and otherwise as sexuallydichromatic, separately for carotenoid- and pheomelanin- andeumelanin-based coloration. We considered sexually dichromaticcolors that were yellow, orange and red to be caused by carotenoids, those with chestnut and brown to be caused by pheomelanin and those with black colors to be caused by eumelanin (seeGray (1996), Tella et al. (2004), Olson and Owens (2005), Møller
and Mousseau (2007b) and Galván et al. (2011) for similar
criteria).
2.2.2. Migration distance
We have previously shown that migration distance predicts
susceptibility to radiation, apparently because free radicals produced by migration and radiation compete for antioxidants (Møller
and Mousseau, 2007b). We recorded the northernmost and southernmost breeding and wintering latitude to the nearest 0.1° latitude based on the distribution maps in Cramp and Perrins(1977–1994). Migration distance was the difference in the meanof the two breeding latitudes and the mean of the two wintering
latitudes.

2.2.3. Dispersal distance
We have previously shown that dispersal distance predicts susceptibility to radiation, apparently because free radicals produced
by dispersal and radiation compete for antioxidants (Møller andMousseau, 2007b). We estimated maximum dispersal distance as
the minimum distance from the mainland to an island with a permanent breeding population, using information in Cramp and Perrins (1977–1994). We achieved this by considering the distancefrom the mainland (usually the European mainland for species
with a Western Palearctic breeding distribution) to all islands closer than the furthest island from the mainland (these islands include among others Azores, Madeira, Canary Islands, Iceland, andthe islands in the Mediterranean), including those that do not currently hold permanent populations (Møller and Mousseau, 2007b).
Therefore, the estimate of maximum dispersal distance was a minimum estimate because many populations on islands are likely not
to have taken the shortest route from the mainland to an island,and because islands may have been colonized directly rather thanby using intermediate islands as stepping-stones.
As alternative estimates of dispersal distance we used geometric mean natal and breeding dispersal distances based on recoveries or recaptures of birds ringed in the UK (Paradis et al., 1998).
These estimates differ from those reported above by Møller andMousseau (2007b) because we do not know if the estimates by Paradis et al. accounted for effective dispersal since information on
breeding status was missing. Previous studies have shown thatgeometric natal and breeding dispersal distances provide important information on the ecology of birds even beyond UK (e.g. Paradis et al., 1998; Belliure et al., 2000).

A.P. Møller, T.A. Mousseau / Biological Conservation 144 (2011) 2787–2798

We used a third estimate of dispersal distance based on relativerichness of subspecies in relation to the size of the breeding range(Belliure et al., 2000). This estimate assumes that a shorter dispersal
distance will result in greater phenotypic differentiation and hence
a greater richness of subspecies per unit area of the breeding range(Belliure et al., 2000). To estimate relative richness of subspecies we
extracted information on number of subspecies from Cramp andPerrins (1977–1994). We estimated breeding range in the Western
Palearctic and total breeding range as the area of the shape boundedby the greatest span of latitude and longitude of each species’
breeding range, as published in Cramp and Perrins (1977–1994).
To take into account the curvature of the earth (which was assumed
to be spherical), this area was estimated by the equation

Area ¼ R2  ðLongitude1  Longitude2 Þ  ðsinðLatitude1 Þ sinðLatitude2 ÞÞ;
where R is the radius of the earth (6366.2 km) and latitude and longitude are expressed in radians.
In widespread species Old and New World ranges were calculated separately and subsequently summed. The method over-estimates true geographical range, but the error should be randomwith respect to the variables investigated here. Estimates of area
were strongly positively correlated with geographical range size
as calculated by counting one-degree grid cells overlain on published distribution maps for a sample of 20 Palearctic and Nearctic
bird species (r = 0.87, P < 0.001), and with range size as reported fora sample of 11 threatened species (Stattersﬁeld and Capper, 2000)(r = 0.98, P < 0.001, based on log-transformed data).
Thus, the different estimates of dispersal distance may accountfor different aspects of dispersal.

2791

males during the breeding season from Cramp and Perrins (1977–1994), again generally preferring estimates from the UK due to larger sample sizes. Body mass was estimated as the mean value ofthe means for males and females.
The entire data set is reported in the Supplementary material in
the electronic Apendix 1.
2.3. Mitochondrial DNA substitution rates
Species-speciﬁc mtDNA base pair substitution rates were used
as reported by Nabholz et al. (2008, 2009). Brieﬂy, complete cytochrome b sequences for 1571 bird species were aligned andchanges in the third base-pair of amino acid encoding codons wereused as a measure of genetic divergence (Nabholz et al., 2009).
Such changes in the third base-pair of amino acid encoding codons
are most often synonymous with respect to amino acid changes
and are thus not usually under selection. The third codon position
substitution rate provides a good approximation of synonymous
substitution rate for two different reasons. First, the vast majorityof the cytochrome b divergence is synonymous (the ratio non-synonymous/synonymous divergence is close to 2% (Nabholz et al.,2008; Stanley and Harrison, 1999). Second, all the transition substitutions (A M G and T M C) of the cytochrome b third codon position are synonymous and most of the substitutions are transitions(the ratio transition/transversion being typically larger than 15 in
the dataset). The 1571 species analyzed by Nabholz et al. (2008,2009) were reduced to 62 species because information on sperm
was only available for this reduced subset of species. Studies havesuggested that most mutations that occur through oxidative DNA
damage are transitions (Wang et al., 1998; Nabholz et al., 2008).
2.4. Measuring background radiation levels

2.2.4. Egg mass
We have previously shown that egg size predicts susceptibility
to radiation, apparently because of competition for antioxidants
between egg production and exposure to radiation (Møller andMousseau, 2007b). We recorded egg mass (g) from Cramp and Perrins (1977–1994). If multiple estimates were provided, we extracted the information from UK because those estimates weregenerally based on the largest sample sizes.
2.2.5. Habitat generalism
Habitat generalism predicts the ability of different species to exploit habitats, with specialists having a narrow niche and generalists a broad niche, thus being able to live in many different places(e.g. Futyuma and Moreno, 1988; Julliard et al., 2006). We recorded
the number of breeding habitats by using the breeding habitat sections in Cramp and Perrins (1977–1994). These authors deﬁned apriori the principal habitat categories in a glossary, and only used
these for characterization of habitat use. We counted these habitat
categories in the breeding habitat descriptions of each species, andthis index was used as a measure of habitat generalism (Belliure
et al., 2000). Because our study was made independently of the habitat preferences in Cramp and Perrins (1977–1994), we can be assured that we have not introduced any bias in our classiﬁcation.
As a second measure of habitat specialization we used the habitat specialization index developed by Julliard et al. (2006), deﬁned
as the variance in population density among 18 different habitat
classes in a nation-wide survey of breeding birds in France. The index values were retrieved from Clavel (2007).
2.2.6. Body mass
We have previously shown that body size predicts susceptibility to radiation, apparently because production of free radicals
and hence use of antioxidants depends on body size (Møller andMousseau, 2007b). We extracted mean body mass of males and fe-

We measured radiation in the ﬁeld and cross-validated thesemeasurements with those reported by the Ukrainian Ministry of
Emergencies. Once having ﬁnished the 5 min census we measured
a, b, and c radiation levels at ground level directly in the ﬁeld at
each point where we censused invertebrates using a hand-held
dosimeter (Model: Inspector, SE International, Inc., Summertown,
TN, USA). All measurements were made according to the instructions for the dosimeter. We measured levels 2–3 times at each site
and averaged the results. We cross-validated our measurements
against data from the governmental measurements published by
Shestopalov (1996), estimated as the mid-point of the ranges published for that particular site. This analysis revealed a very strong
positive relationship (linear regression on log–log transformed
data: F = 1546.49, d.f. = 1252, r2 = 0.86, P < 0.0001, slope (SE) =1.28 (0.10)), suggesting that our ﬁeld estimates of radiation provided reliable measurements of levels of radiation among sites.
The measurements by the Ministry of Emergencies were obtainedby repeated standardized measurement of radiation at the groundlevel in a large number of different localities in Ukraine. Radiationlevels vary considerably at very short geographical distances dueto heterogeneity in the deposition of radiation after the Chernobyl
accident (Fig. 1; Shestopalov, 1996), and our measurements at thecensus points ranged from 0.01 to 379.70 lSv/h, or more than fourorders of magnitude.
2.5. Comparative analyses
Because of common ancestry, comparative analyses based on
species-speciﬁc data overestimate the number of independent
observations, thus increasing the risk of statistical type I errors.
In order to identify evolutionary independent comparisons weused the method of independent contrasts (Felsenstein, 1985) as
implemented in the Macintosh-based software CAIC, using the2792

A.P. Møller, T.A. Mousseau / Biological Conservation 144 (2011) 2787–2798

CRUNCH algorithm (Purvis and Rambaut, 1995). To do this we constructed a composite phylogeny of all species in our data base(Fig. 1 in electronic Supplementary material 2), based on Sibley
and Ahlquist (1990), and updated with recent phylogenies of amore limited range of taxa (Hackett et al., 2008; Jønsson andFjeldså, 2006). All branches were assigned the same length, because there is no phylogeny based on a single genetic marker that
includes all the species included in this study. This procedure isequivalent to assuming an explicit punctuational model of evolution (Purvis and Rambaut, 1995). In alternative analyses we obtained uneven branch length estimates directly from CAIC under
the assumption that the ages of taxa are proportional to the number of taxa they contain. This is equivalent to a gradual model of
evolution (Purvis and Rambaut, 1995). This second series of analyses provided similar results, and for brevity we thus only report theresults from the punctuational models here. Deleting contrasts
with extreme residuals to test the robustness of the conclusions
did not change the results (Purvis and Rambaut, 1995). Contrasts
were analyzed by forcing regressions through the origin, because
the dependent variable is expected not to have changed if there
is no change in the independent variable (Harvey and Pagel, 1991).
2.6. Statistical analyses
We used generalized linear models throughout. We used an error distribution as appropriate for the response variables. Totalabundance of species across all census points, migration distance,
dispersal distance, egg mass, body mass and radiation level were
log10-transformed. We included all main effects in maximal models, eliminating terms using F-tests for model selection (Crawley,
2002). The statistical signiﬁcance of each variable was tested inturn using a backward stepwise procedure. The ﬁnal model wasreached when all variables had a signiﬁcant effect at P < 0.05.
We compared the observed distribution of individuals for different species to the expected random distribution to test if the distribution deviated from what would be expected if individuals were
distributed according to availability of sites. We also calculated
the mean level of radiation at the 731 census points and compared
the observed mean level of radiation with this random expectation.
We tested if the mean level of radiation for the occurrence ofdifferent species was independent of total abundance, with thealternative hypothesis that rare species should be disproportionately frequent in areas with low radiation and hence high species
richness under the hypotheses reported in Section 1.
We tested if rare species were distributed randomly with respect to local species richness and background radiation level,using the census points as independent observations. In this model,
we subtracted the number of rare species from local species richness in order to make the two variables statistically independent.
We developed best-ﬁt statistical models to assess the relationship between abundance (response variable) and carotenoid- andeu- and pheo-melanin-based sexual coloration, migration distance,
dispersal distance, egg mass, body mass and background radiationlevel, using the approach described above.
We estimated effect sizes as a reﬂection of the strength of relationships, using Pearson product-moment correlation coefﬁcients as our
metric. We used the guideline by Cohen (1988) that correlation
coefﬁcients of 0.10, 0.30 and 0.50, respectively, explaining 1%, 9%
and 25% of the variance, are weak, intermediate and strong effects.
All analyses were made with SAS (2000).
3. Results
We ﬁrst present results about the short-term ecological effectsof radiation on abundance and species richness, followed by a sec-tion on the long-term evolutionary effects of radiation on mutations and mutation accumulation.
3.1. Are rare species particularly susceptible to radioactive
contamination?
We recorded a total of 5101 individual birds belonging to 87
species at 731 census points varying in abundance from 1 to 966
individuals for the chafﬁnch Fringilla coelebs, the most abundantspecies that occurred at 581 of 731 census points, or 79% of all
points. Median level of background radiation at the 731 census
points was 0.85 lSv/h, allowing us to test if the observed mean level of radiation at points with occurrence of a given species deviated from the random null expectation of 0.85 lSv/h. The
observed mean level of background radiation at census points withoccurrence of a given species minus the expected level of 0.85 lSv/
h should be distributed binomially with half the species having a
positive difference and the other half a negative difference. In fact,
69 species had negative differences, while only 18 had positive differences, a highly signiﬁcant deviation from the binomial expectation (G = 31.90, d.f. = 1, P < 0.0001). Thus, most species were on
average found at mean radiation levels that were lower than expected from a random distribution. A total of 29 out of 87 species,
or 33.3%, deviated signiﬁcantly from a random distribution acrosslevels of radiation, against the expected 5%; a highly signiﬁcant difference (G = 68.94, d.f. = 1, P < 0.0001). Finally, mean level of radiation at points of occurrence for the different species was tested
against the expected mean value of 0.85 lSv/h. The mean value
for the 87 species was 0.45 lSv/h (SE = 1.121; back-transformed
from the logarithmic data), differing signiﬁcantly from theexpected value of 0.85 lSv/h (one-sample t-test, t = 5.66, d.f. =86, P < 0.0001).
The total abundance of a species across all census points was
signiﬁcantly positively related to the mean level of radiation at
occupied sites (Fig. 2). Thus, globally common species were foundat more radioactive sites than globally rare species. The absolute
frequency of rare species (with a total abundance of 1–5 individuals across all census points) decreased signiﬁcantly with level ofradiation (Fig. 3A; F = 9.58, d.f. = 1729, r2 = 0.013, P = 0.0020, slope(SE) = 0.009 (0.003)). The frequency of rare species was not randomly distributed among census points differing in species richness, with more rare species tending to occur at census points
with higher species richness (Fig. 3B; F = 19.32, d.f. = 1729,
r2 = 0.026, P < 0.0001, slope (SE) = 0.068 (0.015)). The effects ofradiation and species richness on frequency of rare species at census points were statistically independent, with a stronger effect ofspecies richness than radiation (partial effect of radiation: F = 5.03,
d.f. = 1728, r2 = 0.007, P = 0.025, slope (SE) = 0.007 (0.003), effectsize = 0.08; partial effect of species richness: F = 8.41, d.f. = 1728,
r2 = 0.011, P = 0.0039, slope (SE) = 0.050 (0.017)), effect size = 0.11.
Thus, rare species were more common at low radiation levels.
We have previously shown that species that are less common at
the most contaminated sites have carotenoid- and phaeomelaninbased plumage, long distance migration, long-distance dispersal
and relatively large eggs for their body size (Møller and Mousseau,
2007b; Galván et al., 2011). Therefore, we modeled the total abundance of bird species in relation to radiation and the previously
identiﬁed ﬁve variables, with a statistical model that explained
41% of the variance (Table 1). There was a signiﬁcant effect of dispersal distance with species with long dispersal distances being
globally more abundant across all sites (Table 1). Unsurprisingly,
small-sized species were globally more abundant than large species (Table 1). Finally, species that occurred at higher radiation levels were ones that tended to be generally the most abundant acrossall sites (Table 1). There were no signiﬁcant effects of carotenoidor phaeomelanin-based coloration. An analysis of independent

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A.P. Møller, T.A. Mousseau / Biological Conservation 144 (2011) 2787–2798

Fig. 2. Total abundance of 87 species of breeding birds around Chernobyl across all census points in relation to the mean level of radiation (lSv/h) at census points where a
species was recorded. The positive relationship implies that rare species occur at the least contaminated areas, whereas abundant species are found in the most contaminatedareas.

Table 1
Total abundance of 87 different bird species around Chernobyl in relation to dispersal
distance (km), body mass (g) and level of background radiation (lSv/h) in analyses of
species-speciﬁc values and statistically independent linear contrasts. All variables
were log-transformed before analysis. The two models had the statistics F = 19.15,
d.f. = 3,83, r2 = 0.41, P < 0.0001 and F = 25.98, d.f. = 2,84, r2 = 0.24, P < 0.0001.
Variable

Sum ofsquares

d.f.

F

P

Slope (SE)Species
Dispersal distance
Body mass
Radiation
Error

2.455
2.070
13.78027.877

1
1
1
83

7.31
6.16
41.03

0.00830.015<0.0001

0.298 (0.110)
0.259 (0.104)
0.544 (0.085)

Contrasts
Dispersal distanceRadiation
Error

0.483
3.909
7.938

1
1
84

5.11
41.37

0.026
<0.00010.240 (0.106)
0.539 (0.084)

retained (Table 1). There were no signiﬁcant effects of carotenoidor phaeomelanin-based coloration.
We tested if the effect of radiation on overall abundance acrossall sites remained after inclusion of habitat generalism as an additional predictor variable. Only the habitat specialization index entered this model, while the number of breeding habitats was notincluded because it explained hardly any of the variance (Table 2).
This model for species-speciﬁc data that only included habitat specialization index and radiation level accounted for 44% of the variance (Table 2). The effect of radiation was still the best predictor,
accounting for 23% of the variance and hence a large effect, while
the effect of habitat specialization accounted for 14% of the variance (Table 2). Both these effects were conﬁrmed in analyses of
independent contrasts (Table 2).
3.2. Mutational load and radiation
Fig. 3. (A) Frequency of rare species of birds at census points around Chernobyl in
relation to background radiation levels (lSv/h). Rare species had a total abundanceof 1–5 individuals recorded during 2006–2008. Values are means (SE) for census
points. (B) Frequency of rare species of birds at census points around Chernobyl in
relation to local species richness at census points. Rare species had a totalabundance of 1–5 individuals recorded during 2006–2008. Values are means (SE)for census points.

contrasts revealed signiﬁcant effects of dispersal distance and radiation on overall abundance, while the effect of body size was not

Mutations are generally slightly deleterious, although rare beneﬁcial mutations do occur (Eyre-Walker and Keightley, 2007). Because mutation rates in the male germline generally exceed
those in the female germline because of the larger number of cell
divisions, especially in older individuals (Crow, 1997), we evaluate
the consequence of such sex-bias for mutational load. Crow (1997)
discussed at length the health risks that slightly deleterious mutations pose to human societies. The three main points were that (1)substitution rates are higher in males than in females, especially in2794

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Table 2
Total abundance of 65 different bird species around Chernobyl in relation to habitat specialization and level of background radiation (lSv/h) in analyses of species-speciﬁc values
and statistically independent linear contrasts. Radiation level was log-transformed before analysis. The two models had the statistics F = 24.26, d.f. = 2,62, r2 = 0.44, P < 0.0001 andF = 25.95, d.f. = 2,62, r2 = 0.30, P < 0.0001.
Variable

Sum of squares

d.f.

F

P

Slope (SE)Species
Habitat specialization
Radiation
Error

2.813
5.327
17.984

1
1
62

9.70
18.36

0.0028<0.0001

0.939 (0.301)
0.416 (0.010)

Contrasts
Habitat specialization
Radiation
Error

0.562
1.510
4.463

1
1
62

7.81
20.98

0.0069<0.0001

0.812 (0.290)
0.419 (0.092)

older individuals, due to a large number of cell divisions in themale germline. (2) The number of mutations per generation exceeds the number of zygotes. (3) The most efﬁcient way in whichorganisms can cope with a high mutation rate is through quasitruncation selection (instead of a speciﬁc cut-off point the probability of selective elimination increases gradually over the rangeof number of mutations; Crow and Kimura, 1979) resulting inselective deaths with each eliminating a number of mutated genes.
Comparative analyses in birds have shown that species with higher
frequencies of extra-pair paternity and later age at ﬁrst reproduction have higher male to female mutation bias (Bartosch-Härlid
et al., 2003). This sex-biased mutation effect is exacerbated by a female-biased mortality in contaminated areas around Chernobyl
resulting in a preponderance of male-biased tertiary sex ratios(Møller et al., 2005a). This should result in a relatively fewer males
contributing genetically to the next generation with subsequentconsequences for the effective population size.
How do we estimate mutation effects from Chernobyl? One way
is to rely on mutation estimates and their consequences in humans
and Drosophila. Eyre-Walker and Keightley (1999) used DNA substitution data for humans since divergence from the chimpanzee
Pan troglodytes to estimate the number of deleterious mutations
per zygote. They found a total of 143 non-synonymous substitutions and 231 neutral mutations, and the difference between these
two estimates equals 88 deleterious mutations, which account for
88/231 = 38% of mutations having been eliminated through selection. Using an estimated generation time of 25 years gives 1.6 deleterious mutations per zygote per generation. The estimate of thefraction of deleterious mutations may be too low, the time since
chimpanzees and humans diverged is estimated with uncertainty,
and mutations outside coding regions were disregarded (EyreWalker and Keightley, 1999). In conclusion, Eyre-Walker and
Keightley (1999) suggested a deleterious mutation rate of three
new mutations per zygote, and similar levels may apply to othervertebrates.
We can use this estimate to assess the effects on genetic deaths
caused by the effects of deleterious mutations on the probability ofsurvival and reproduction. If ﬁtness is multiplicative,then the probP
ability of survival and reproduction equals e2 lP, where l is themutation rate P(Crow, 1997). So if l = 1, then e2 l = 0.37, and if
l = 3, then e2 l = 0.05. With the ﬁrst estimate of one deleterious
mutation per zygote, we end up with the rule of Muller (1950) thateach mutation leads to a genetic death. However, if mutation rates
increase by up to a factor 20, as reported from Chernobyl (Møller
and Mousseau, 2006), then the number of genetic deaths would
be prohibitively high. How can we resolve this dilemma? Twomechanisms may resolve this problem. First, truncation selection
has a ﬁxed threshold of number of deleterious mutations beyond
which all individuals die potentially resulting in elimination of multiple mutations. Crow and Kimura (1979) showed that quasi-truncation selection where the probability of selective elimination

increases gradually with the number of deleterious mutations is almost as efﬁcient as truncation selection, with the efﬁciency reaching 87% under realistic assumptions about the distribution of
mutations. Thus selective deaths simultaneously eliminate a number of mutations rather than just a single deleterious mutation. Second, deleterious mutations may not be distributed randomly acrossthe genome. For example, Forster et al. (2002) showed for mitochondrial DNA in humans in response to natural variation in background radiation that mutations were strongly aggregated. Thiseffect will contribute to simultaneous elimination of deleterious
mutations. Likewise, genomic instability reﬂects the situation
where particular parts of the genome are susceptible to breakage
across generations, as reported for humans and mice exposed toradiation (Morgan et al., 1996; Dubrova et al., 1998), and such
instability will tend to cause aggregation of mutations.
The mean number of generations that a slightly deleterious mutant persists in a population is also of importance because it willaffect the probability of the mutant migrating outside the area ofcontamination, but it will also affect the number of generations
during which we might be able to detect viability reduction underﬁeld conditions. We can estimate this quantity from the reduced
viability of heterozygotes and the mutation rate per zygote. The reduced viability due to minor deleterious mutants has been estimated to 0.12 (Temin, 1966). Crow (1997) reviewed estimates ofnumber of generations that deleterious mutants persisted in Drosophila populations as 33–167, with a mean estimate of around80 generations. Thus, if we assume one deleterious mutation per
zygote per generation, this implies that an average fruitﬂy carries
80 mutations. Therefore, we can expect mutations and their ﬁtness
effects due to the initial release of radiation from the Chernobyl
nuclear reactor in 1986 to persist for a very long time. For example,
humans are still in the ﬁrst generation after the accident (assuming
a generation time of 30 years), suggesting that any full assessmentof the effects of mutations must await the next many generations.
Given that most of the radioactive Cs, Sr and Pu isotopes are stillpresent due to their long half-lives, we can expect mutational effects and high levels of genetic deaths for a very long time. We
can also expect the level of these genetic deaths to be high,although exact estimates will require further information on themagnitude of the component parts of the model.
If dispersal distance was correlated with mutation rate, this
could determine which species would suffer the most from migration of mutants outside the most contaminated areas around Chernobyl. We made a preliminary test of this idea by relatinggeometric mean natal and breeding dispersal distance to mitochondrial DNA substitution rate. The latter is positively related tothe effect of radiation from Chernobyl on the abundance of birds(Møller et al., 2010). While there was no signiﬁcant relationshipbetween substitution rate and natal dispersal distance in a modelthat also included body mass as a predictor variable (F = 0.78,
d.f. = 1, 23, P = 0.39, slope (SE) = 0.135 (0.154)), the relationship

A.P. Møller, T.A. Mousseau / Biological Conservation 144 (2011) 2787–2798

with breeding dispersal distance was signiﬁcantly negative(F = 7.75, d.f. = 1, 23, P = 0.011, slope (SE) = 0.344 (0.124)). Thisﬁnding suggests that mutations are less likely to be spread touncontaminated areas through dispersal in species that are mostsusceptible to mitochondrial mutations, while species with few
mutations are more likely to suffer from the effects of such mutations beyond the immediate area of contamination.
In a second series of analyses we related mitochondrial DNA
substitution rate to subspecies richness, adjusted for breeding
range size and body mass. Indeed, mitochondrial substitution rate
was signiﬁcantly larger in species with higher subspecies richness(F = 11.07, d.f. = 1, 149, P = 0.0011, slope (SE) = 0.213 (0.064)), afterpartialling out the effect of body mass (F = 131.85, d.f. = 1149,
P < 0.0001, slope (SE) = 0.322 (0.028)). The effect of breeding
range size was not statistically signiﬁcant (F = 0.72, d.f. = 1, 148,
P = 0.61, slope (SE) = 0.023 (0.044)). Therefore, mitochondrial
DNA substitution rate increased with decreasing dispersal distance, a conclusion that is consistent with the conclusion fromthe analyses of geometric natal and breeding dispersal distances
reported above.
4. Discussion
The main short-term ecological consequences of radiation from
Chernobyl were that most species of birds occurred disproportionately often at low radiation levels. Abundant species occurred botha census points with low and high radiation levels, while rare species were restricted to sites with low radiation levels and high species richness. These effects of radiation on abundance were
unaffected by potentially confounding variables such as dispersal
distance and habitat specialization. The main long-term evolutionary consequences were that mutation rates have increased by up toa factor 20 due to release of radionuclides from Chernobyl. Each
such slightly deleterious mutation is expected to result in a selective genetic death. Because average slightly deleterious mutation ispresent for 33–167 generations in Drosophila, mutants will disperse outside contaminated areas resulting in the spread of mutations well beyond the reach of contamination with radionuclides.
The Chernobyl disaster and other nuclear releases may have significant consequences for population size and population viability ofmany species due to the large number of selective deaths. Because
elevated mitochondrial DNA substitution rates occurred in bird
species with short dispersal distances, mutations will spread relatively short distances in species where they are common, but longer distances in species with less common mutations.
4.1. Radiation and rarity in birds
The effects of the nuclear disaster at Chernobyl on conservation
are poorly understood. Extensive areas covering more than
5000 km2 in Ukraine and Belarus are now largely abandoned without agricultural activity (although forestry activities are conductedto prevent excessive forest ﬁres). Obviously, this has conservation
implications because most organisms do better in the absence ofhuman disturbance. Hence, it would not be surprising if the abundance of animals and other organisms had increased in these areas,
were it not for the presence of radioactivity. Some scientists haveattempted to brand the Chernobyl Exclusion Zone as a wildlife preserve promoting it as a UN cultural heritage site. Others have released a herd of 35 Przewalski’s horses Equus ferus przewalskii
inside the Exclusion Zone (Zharkikh and Yasynetska, 2008), apparently without considering the risk of contamination of the germline of this exceedingly rare species with unwanted mutationalload. However, all taxa investigated so far have shown reduced,
sometimes dramatically reduced abundance with increasing level2795

of background radiation (Møller and Mousseau, 2011). Here wehave reported the results of extensive analyses of bird census datafrom Ukraine and Belarus to assess the extent to which rare species
differed in their response to radioactive contamination from moreabundant species. Generalists that occurred in high abundancewere found across a wide range of background radiation levels,
while rare species were concentrated in relatively uncontaminatedareas. The latter areas were also characterized by high species richness that was an independent predictor of the frequency of rare
species. Thus, rare species were predominant in areas with highspecies richness and low levels of radioactivity. Among these rare
species recorded in this study there were no directly threatenedor endangered species in the study areas although a signiﬁcant
fraction of the globally threatened aquatic warbler Acrocephalus
paludicola breeds in Belarus and Northern Ukraine (Cramp and Perrins, 1977–1994).
We have so far only considered the direct effects of radioactive
contamination on the abundance of bird species. However, there
are good reasons to believe that radioactive contamination has increased the importance of parasites in regulating the size of their
host populations (Yablokov et al., 2009). This may act through at
least two mechanisms. First, increased mutation rates may provide
parasites with a selective advantage in the exploitation of theirhosts because such hosts will be unable or less able to defend
themselves against novel parasite genotypes, and there is direct
evidence that bacteria have increased their mutation rates considerably (Ragon et al., 2011). Second, radionuclides may directly
weaken the ability of hosts to defend themselves, as in the caseof immune defenses of humans against viral and bacterial parasites(Yablokov et al., 2009), or because plants such as wheat Triticum
aestivum which suffer from reduced proteinase inhibitors that allow wheat rust Puccinia graminis to increase its rate and intensityof attack on wheat plants (Dmitriev et al., 2007).
4.2. Mutation rates and mutational load
Populations of barn swallows Hirundo rustica and other bird
species in the surroundings of Chernobyl cannot be maintained
through local recruitment due to low annual adult survival rates
and fecundity (Møller et al., 2005a, 2008). Part of this excess mortality may be caused by mutational effects. Given that populationsof barn swallows and other species are still present despite low
adult survival rates and fecundity implies that immigrants fromnearby populations ﬁll vacancies in contaminated areas. We havealready published information based on stable isotope proﬁlesconsistent with such source-sink dynamics (Møller et al., 2006).
Mutation rates in a diverse array of organisms from Chernobyl
have shown increases by up to a factor of 20 (Møller and Mousseau, 2006). Such large increases in mutation rates will have consequences for mutational load and the number of selective
deaths needed to eliminate slightly deleterious mutations (Crow,
1997, 2000). In a now classical paper, Muller (1950) suggested that
one genetic death would be expected per slightly deleterious
mutation. If mutation rates are increased considerably above thelevels recorded in radioactively uncontaminated areas, we should
expect a very dramatic increase in the frequency of individuals that
did not survive or reproduce to such an extent that it would be
impossible to maintain viable populations. Given that signiﬁcantlevels of radioactive contamination covers an area of many thousand square kilometers (European Union, 1998), the size of manyof the affected bird populations would be in the millions of individuals. Thus, the number of selective deaths required to eliminate theslightly deleterious alleles would be prohibitively high. There is
ﬁeld evidence suggesting that a very large fraction of females does
not reproduce in species that otherwise rarely or never skip reproduction (Møller et al., 2005a). Likewise, as many as 28% of all males

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A.P. Møller, T.A. Mousseau / Biological Conservation 144 (2011) 2787–2798

from more than 50 species of birds from contaminated areas haveno sperm. Furthermore, adult survival rate of barn swallows fromcontaminated areas is reduced by half compared to populations
from uncontaminated control areas (Møller et al., 2005a). Thus
there is ﬁeld evidence consistent with high mutational loads. We
might partly eliminate the problem of a prohibitively high numberof genetic deaths by the fact that mutations are aggregated on thechromosomes (Forster et al., 2002), and that multiple mutant alleles are likely to be eliminated simultaneously through quasitruncation selection (Crow, 1997, 2000). In any case, the total number of selective deaths caused by slightly deleterious alleles arisingfrom the mutagenic effects of radiation from Chernobyl is likely to
be considerable. Given that the average mutation is likely to persist
in populations for up to a hundred generations before being eliminated (Crow, 1997), mutations may be able to spread across large
distances due to dispersal, causing detrimental effects far beyond
areas that are actually contaminated. For example, Paradis et al.
(1998) reported a mean dispersal distance of 69 species of common
birds of 2.7 km, or 270 km following 100 generations. If we only
consider the most extreme dispersal distances, these distances will
increase more than 10-fold (Paradis et al., 1998), implying that already now such mutants may have migrated to western and southern Europe from the main area of contamination in Ukraine. The
extent of these effects remains to be determined. However, at least
theoretically we should be able to identify the footprint of thisevent as mutants travel away from Chernobyl through migration,
given that numerous deleterious mutations are likely to enter populations of many kinds of organisms due to the mutagenic effectsof radiation from Chernobyl.
There was evidence of signiﬁcant interactions between dispersal and mutations. Comparative analyses revealed signiﬁcantly
lower dispersal distances in species of birds with high mitochondrial DNA substitution rates. That was the case for breeding dispersal distance and relative subspecies richness that is anindirect estimate of dispersal propensity (Belliure et al., 2000). This
association may imply that species with higher mutation rates
transport mutations through dispersal over shorter mean distances
than species with low mutation rates. However, we note that dispersal is notoriously difﬁcult to estimate because a few extreme
dispersers that cover very long distances (Koenig et al., 1996)
may transport mutations far away.
4.3. Future repercussions of the Chernobyl disaster
The Chernobyl disaster may have additional repercussions thatneed to be considered by conservation biologists, and we emphasize two issues: (1) Fire risk and the potential transport of radionuclides outside heavily contaminated areas; and (2) movementof radionuclides, especially trans-uranium elements outside themost contaminated areas with migratory birds and other biologicalagents.
The location of radionuclides is not stable because many different processes including forest ﬁres and ﬁres initiated by humans inagricultural landscapes result in transport of radionuclides outside
the most contaminated areas in Ukraine, Belarus and Russia. During the hot summer 2002 radionuclides from Chernobyl were recorded in Vilnius, Lithuania in a concentration that was
hundredfold higher than normal, and in August 2010 the concentration of 137Cs in Obninsk, Kaluga near Moscow increased threefold, and on certain days 24-fold (Yablokov et al., 2011, p. 343).
Widespread forest ﬁres occurred in contaminated areas during
the exceptionally hot and dry summer of 2010 (Charles, 2010),
and they are likely to be repeated in the future due to climatechange (Barriopedro et al., 2011). In addition, farmers habitually
initiate ﬁres in potato stalks and other crop remains during August–October and dry grass in spring, with thousands of small ﬁres

burning in any fall, increasing concentrations of radionuclides
manifold in the top soil (Dancause et al., 2010) and releasing radionuclides into the atmosphere. Several hundred ﬁres were burningin early August 2010 in the contaminated areas in Ukraine, Belarus
and Russia, many in contaminated areas, and they are likely tohave caused increased levels of 137Cs and trans-uranium elements(TUE) in the air. If major forest ﬁres occur in the future, large
amounts of radionuclides stored in wood could be transported bysmoke and wind to nearby metropolises such as Kiev and Moscow
causing major environmental contamination. Policies that attempt
to mitigate the long-term accumulation of ﬁrewood and the highrisk of forest ﬁres in this area with increasing summer temperatures and drought are urgently needed.
Movement of radionuclides, especially trans-uranium elements,
but also cesium and strontium outside the most contaminatedareas may endanger populations of free-living organisms and humans in areas that are currently little affected by contamination.
Particular interest in TUE is due to the majority of these isotopes
being alpha emitters with high radiotoxicity and high probabilityof cancer development. Most TUE fell near the reactor, but noticeable contamination of soil also took place far from Chernobyl due
to atmospheric transport, with sizeable concentrations in South
Belarus, Western Ukraine and in the vicinity of the Ukrainian capital Kiev. Signiﬁcant levels of contamination have appeared in areas
outside the Chernobyl Exclusion Zone due to transport during thelast 25 years (Ministry of Emergencies of Ukraine and Intelligence
Systems GEO, Ltd., 2011), and a major source of transport is migratory birds. The levels of internal exposure of people living in theseareas exceeds previous predictions manifold. Agricultural activity
increases TUE activity in the air by 50–450 times, thus exceeding
the speciﬁc activity of TUE in the air in the Chernobyl Exclusion
Zone, and TUE activity in the air also increases signiﬁcantly in yearsof large forest ﬁres (Konoplya et al., 2007). We consider such transport of TUE to potentially be of general conservation concern due
to its effects on mutational loads.
In conclusion, we have provided an extensive review of theshort-term ecological consequences of the Chernobyl disaster by
analyzing the relationship between rarity and level of backgroundradiation in birds. In addition, we have provided extensive information on the long-term evolutionary consequences from the frequency of mutations, mutational load and the potential cost of theChernobyl disaster in terms of excess selective deaths. The ecological and evolutionary consequences were linked because bird species with short distance dispersal were those with low
mitochondrial mutation rates. We consider these ecological andevolutionary factors to potentially have strongly negative effects
on the conservation status of many species of birds and by inference also other organisms.
Acknowledgments
A.V. Yablokov and an anonymous reviewer provided constructive criticism. We gratefully acknowledge logistic support and help
in Ukraine by I. Chizhevsky and G. Milinevski, and we thank N. Nelson for continued advice concerning the health impacts of radiation. We gratefully acknowledge support from the US National
Science Foundation, the University of South Carolina School of
the Environment, the NATO CLG program, the CRDF, the Fulbright
Program, the National Geographic Society, and the Samuel Freeman Charitable Trust.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.biocon.2011.08.009.

A.P. Møller, T.A. Mousseau / Biological Conservation 144 (2011) 2787–2798

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