We studied the abundance of the common cuckoo Cuculus canorus L. little cuckoo Cuculus poliocephalus L. and Asian cuckoo Cuculus saturatus L. and avian top predators as indicators of bird species richness (surrogate of biodiversity) in disturbed environments caused by radioactive contamination in Chernobyl, Ukraine and Fukushima, Japan, comparing their efficiency as indicators of local biodiversity hotspots. Bird species richness and birds abundance were quantified in each sample site during the breeding seasons between 2006 and 2015 and the level of background radiation was measured at every site. The correlation between number of cuckoos, top predators, land use composition and level of background radiation with bird species richness as response variable were examined using Generalized Linear Mixed Models. The strength of correlation between species richness and abundance and the covariates obtained from the model outputs were used as measure of the efficiency of each predictor, as well as the AIC of each model. Background radiation was negatively correlated with bird species richness and bird abundance in both countries, while number of top predators and cuckoos were both positively correlated with bird species richness and abundance. However, model with number of cuckoos was more performant than model with number of avian top predators. These differences in performance supports the hypothesis that cuckoos are a largely superior bioindicator than top predators.

Czech University of Life Sciences Prague Faculty of Environmental Sciences Department of Applied Geoinformatics and Spatial Planning Kamýcká 129 165 00 Prague 6 Czech Republic

Department of Biological Sciences University of South Carolina Columbia SC 29208 USA

Ecologie Systématique Evolution Université Paris Sud CNRS AgroParisTech Université Paris Saclay F 91405 Orsay Cedex France

Faculty of Biological Sciences University of Zielona Góra Prof Szafrana St 1 PL 65 516 Zielona Góra Poland

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