Species richness of birds in forests around Chernobyl decreased by more than 50% with increasing level of radiation, and this effect was independent of potentially confounding factors such as time of day, weather, soil type, age of tree stands and habitat. Abundance of birds decreased by 66% between the most contaminated sites and sites with normal background radiation (within the study areas). These results are the first census data reported from Chernobyl, and they indicate dramatic effects on species richness and abundance of birds that play important roles in ecosystem functioning.
We found strong declines in species richness, abundance and population density of birds associated with elevated levels of background radiation near Chernobyl. The conclusions were similar when based on parametric or non-parametric analyses, controlling for potentially confounding variables. We had relatively few observations in the range of 1–10
(). However, the negative relationships were prominent both among data points with a radiation level below and above 5
(), showing that even radiation levels below 5
were associated with reduced abundance. Most radiation around Chernobyl is currently in the topmost layer of the soil (Shestopalov 1996
; European Union 1998
), where soil invertebrates live. Bird species consuming soil invertebrates decreased in abundance more strongly than other species, suggesting that radiation had differential effects on specific functional ecological groups.
We suggest three mechanisms underlying these observed patterns of species richness and abundance of birds in relation to level of radiation. First, radiation may directly reduce survival rates and fecundity, thereby causing extinction or reducing population sizes, as shown previously for the barn swallow Hirundo rustica
(Møller et al. 2005
). Second, birds may avoid radioactively contaminated areas because such areas are suboptimal habitats for birds (Møller & Mousseau 2007
). Third, birds may be less abundant and species richness may be reduced in contaminated areas owing to reduced abundance of invertebrates that constitute the most common food of many species.
We have previously demonstrated significant negative impacts of Chernobyl-related fallout on barn swallow mutation rates, survival and reproduction (Møller 1983
; Ellegren et al. 1997
; Møller et al. 2005
). Here, we extend our observations to document extensive reductions in the species richness, abundance and population density of birds in general with increasing levels of radiation around Chernobyl. These effects are likely to have important implications for other parts of the ecosystem and for overall ecosystem functioning.