Interactive effects of ionizing radiation and climate change on the abundance of breeding birds

The effects of ionizing radiation on living beings have been studied under lab conditions and in the field. The first approach may often lack in realism, while the second may lack rigorous experimental approaches. Because ionizing radiation may interact with other stressors such as heavy metals and climatic conditions, it is difficult to assess the independent effects of such different factors. We conducted extensive breeding bird surveys at Fukushima during 2011-2017 and related the abundance of different species to the ambient level of radiation. Climate warming has affected many parts of the globe suggesting that the effects of ionizing radiation at Fukushima may interact with precipitation and temperature. We assessed the independent and the interacting effects of temperature, precipitation and ionizing radiation for the abundance of breeding birds at Fukushima. We documented strongly negative effects of ionizing radiation on the abundance of 32% of bird species as found in previous studies while 5% would be expected by chance. The main effects of temperature and radiation affected 21% of the species, while the interaction effects of temperature by radiation affected 19%, and the interaction effect of precipitation by radiation only accounted for 8%. While the effects of temperature were significant, similar tests for precipitation effects were not statistically significant. The effects of ionizing radiation on adults was strongly positively correlated with the effects of ionizing radiation on juveniles. These findings imply that the main effects of ionizing radiation were considerable, they were much larger than those of temperature and precipitation, and the interaction effects of temperature and ionizing radiation were significant. The effects on adults was comparable to the effects on juveniles. This first study of interactions between two stressors, ionizing radiation and climate, suggests that it is unlikely that the effects of confounding variables account for the apparent effects of ambient ionizing radiation on bird populations at Fukushima.