In a set of papers published Thursday in the Journal of Heredity, a U.S. publication, Japanese and U.S. scientists warned that radioactive materials released from by the core meltdowns at the Fukushima No. 1 power plant could have caused abnormalities in the genes of nearby birds and insects.

One of the experts, Timothy Mousseau of the University of South Carolina, called for wide-ranging and long-term research on ecosystems, such as a genetic-level analysis, drawing a comparison with what happened to such species after the 1986 Chernobyl disaster in present-day Ukraine.

In a paper published on the journal’s website, Mousseau said barn swallows with abnormal white spots on their plumage were found near the Chernobyl plant after the disaster and that the discovery of similarly plumaged swallows in Fukushima was also reported in the wake of the 2011 crisis.

“Barn swallows with aberrant white feathers were first detected in Fukushima in 2012 and were observed in increasing frequencies in 2013 and 2014,” the paper said.

Mousseau is closely watching for signs of population decline in some birds due to abnormalities in mitochondrial DNA in areas near the Fukushima plant, since the same problem was reported in Chernobyl.

The poorly protected and maintained Fukushima plant, operated by Tokyo Electric Power Co., was extensively damaged by tsunami spawned by the Great East Japan Earthquake in March 2011 and suffered a blackout after losing its cooling systems.

High concentrations of radioactive materials spewed in the world’s worst nuclear accident since Chernobyl forced thousands of residents in Fukushima and elsewhere to flee.

Joji Otaki, associate professor at the University of the Ryukyus in Okinawa Prefecture, said in a separate paper in the same journal that abnormalities in the genes and sizes of pale grass blue butterflies were also detected. They were captured near the Fukushima plant.

Otaki said the abnormality rate for the butterfly, common in many parts of Japan, declined after peaking in September 2011 and that the finding could suggest the species possibly adjusted itself to the new environment and acquired radiation resistance after the meltdowns.