Growing up can be tough. You might imagine it would be even tougher in the Chernobyl Exclusion Zone (CEZ), the roughly 1,000 square mile expanse of northern Ukraine left contaminated by the 1986 nuclear power plant explosion. But for baby birds born in the Zone, it’s actually far more complicated.
New research indicates that nestlings in highly radioactive parts of the CEZ do experience subtle biological differences from those reared in clean areas. Yet those differences might not impact overall health and survival. At the Society for Experimental Biology Annual Conference on July 3, Sameli Piirto, a PhD researcher at the University of Jyväskylä in Finland, presented early findings related to baby birds’ health and microbiomes in different areas of the CEZ.
“There’s been lots of studies of Chernobyl [wildlife] in the past couple of decades, and something that’s been lacking so far is the perspective of young animals in the contaminated environment,” Piirto tells Inverse. Unlike adult animals and many mammals that have been studied, nestlings can’t move and are subject to their immediate environmental conditions. For researchers, “it is one of the big advantages of [breeding] birds,” Piirto notes — that you have an animal, stationary for weeks, which you can compare to other nestlings and related adults.
Using data from 300 nest boxes placed across the Zone, Piirto sought to evaluate nestlings of two different bird species: great tits (parus major), a resident species, and pied flycatchers (ficedula hypoleuca), which are migratory. His research colleagues had installed half of the nest boxes in areas of the CEZ with low levels of radiation that were considered “clean” and half in highly radioactive areas, considered “hot.”
There was broad variation in radiation levels across the sites. Some clean areas measured close to the standard background level of radiation one might find anywhere (about 0.34 microsieverts per hour, on average, in the United States). The worst of the hot sites, meanwhile, measured at about 100 microsieverts per hour, which is like “getting a chest X-ray every hour,” says Piirto. Over time, that level of radiation exposure would add up to about 870 times the recommended annual exposure limit for members of the general public, and carry significant health risks for a human.
In 2021 Piirto’s colleagues monitored the inhabited boxes and the birds within, collecting stool and blood samples from adults and two nestlings at each location. Piirto later analyzed that data, looking for signs that bird breeding behavior or baby bird health differed between hot and clean zones.
Past studies of Chernobyl’s wildlife have yielded mixed outcomes. Some research frames the CEZ as a biodiverse haven, free from the influence of destructive humans with an amazing array of species living in relative peace. Other studies have suggested that parts of the CEZ aren’t so biodiverse– comparatively lacking in organisms from birds to soil invertebrates. A handful of research papers indicate that some animals living in the CEZ may be suffering the consequences of radiation exposure.
The full impacts of the Chernobyl disaster on wildlife may never be completely understood, says Piirto. Taking humans out of the equation does seem to offer significant benefits to many animals. The radiation levels across the zone are very heterogeneous — in some places, persistent contamination is minimal. And it’s hard to separate the potential impacts of radiation from other factors, like habitat differences or weather events that might stir up dangerous and otherwise dormant dust.
The full impacts of the Chernobyl disaster on wildlife may never be completely understood, says Piirto.
Then there’s the difficulty of interpreting nuanced results like Piirto’s. Across the nest boxes, Piirto and his co-researchers did find that boxes in hot zones were less likely to be occupied than ones placed in clean areas (36.6 percent versus 57 percent occupancy rates). There were also hints that continuous radiation exposure might delay the breeding timeline (though these findings didn’t reach the threshold of statistical significance). But overall, nestlings in each type of site appeared equally healthy, with equivalent brood sizes, body condition, and chick weights. “We didn’t find big differences in breeding success of the birds,” says Piirto.
Things get even more confounding from there. Through poop samples, Piirto was able to determine what each nestling and adult bird was eating. He found that radiation levels didn’t negatively impact the diversity of insects in the birds’ diets. In fact, nestlings were eating equivalent amounts of different taxa in hot and clean zones. However, the composition of that dietary diversity differed between the two site types. In more contaminated areas, birds of both species ate more butterflies and moths than birds in clean zones. In clean areas, flies were a more common food source. This is oddly counterintuitive, he points out, as butterflies and moths are generally considered more sensitive to environmental degradation than flies. Further, forest type was also a significant influence on diet, indicating radiation is far from the only factor at play.
Finally, Piirto assessed the birds’ microbiomes —the assemblage of bacteria inside their guts that numerous human and animal studies indicate has a big impact on health across species. Again, he found that the number of different types of microbes was about the same across nest sites, but that there were compositional contrasts between the birds in hot and clean zones. “The microbiome of individuals is way different in the hot area,” Piirto says. Different microbe groups are dominant in each species based on nest location. These results echo past findings on the microbiome of small mammals called bank voles in the Zone. However, what it means for the birds is still unclear.
“We have this image of Chernobyl being this mutating, super hazardous environment in which all manner of weird things happen.”
“It might refer to metabolic stress that the animals are experiencing,” Piirto posits —but there’s not yet clear evidence for that. “Microbiome is super complicated– it’s a community of things that affect your food intake, your metabolism, and your immunity,” he says. And it’s much more well-studied in humans than it is in birds. Without more information, he says any ideas about how the microbiome differences across the CEZ are impacting birds remain guesses.
Altogether, the research indicates that something is different about birds who nest in highly radioactive areas, but perhaps not to the degree expected. What it means for population success and survival over the long-term remains a mystery. Piirto is currently conducting related analysis, looking more closely at the nestling blood samples and measuring markers of immune health. Results there are pending, and far from finalized, but Piirto hints that there may be some detectable trends in that forthcoming work as well.
“I have been surprised,” he notes. “We have this image of Chernobyl being this mutating, super hazardous environment in which all manner of weird things happen.” So far though, that cultural conceit hasn’t quite borne out in the science. “There are some differences. They may not be the ones I expected, but they are quite intriguing.” “We cannot assume,” Piirto says. “That’s why we study different organisms and environments and systems — because we want to understand nature. And sometimes nature surprises us.” Still though he doesn’t recommend anyone pack up and go move to the CEZ. “It’s complicated, but don’t go to live in Chernobyl yet.”
