Normal Barn Swallow (a),
while the other pictures show signs of albinism (white feathers; b & c),
unusually colored feathers (d), deformed beaks (e & f), deformed air sacs (g),
and bent tail feathers (h & i).
Images: Tim Mousseau.
Twenty years after the Chernobyl reactor disaster, which released clouds of radioactive particles in April 1986, the uninhabited forests within the 19 mile (30 kilometer) “exclusion zone” around the disaster site are lush and teeming with wildlife, giving the appearance that nature’s wounds are healing. However, to the trained eyes of the naturalist, something is seriously wrong here.
In fact, many birds in the area show obvious abnormalities such as deformed beaks, toes, and feathers and unusual coloring (see figure, top). Additionally, the overall abundance of bird populations were noticeably diminished, and individuals were not living as long and were not breeding as successfully as those birds of the same species that live far away. Further, some species that should be present were nowhere to be found or had dwindled to very low numbers.
Upon closer examination, the greatest population decreases were documented for birds with vibrant plumage, and for those species that lay large eggs or migrate over long distances. According to researchers, these particular traits require lots of antioxidants — molecules that are also essential to protect against radiation damage. Thus, when these other physiological demands diminish the level of antioxidants, this leaves fewer to counteract the effects of radiation.
“Overall we found that population size and abundance decreased,” said Timothy Mousseau, of the University of South Carolina in Columbia, SC. “However, a few species actually increased in contaminated areas — we don’t know why, but it could be due to decreased competition in these areas. The take-home message is that there is tremendous variability in the way that different species cope with radiation.”
To collect data for this study, Mousseau and his colleague, Anders Pape Møller, from the University of Pierre and Marie Curie in Paris, counted more than 1,500 birds at 254 sites in the woods near the reactor, and compared areas with high radioactivity to nearby uncontaminated sites.
First, they found that birds in the Chernobyl nuclear disaster study area have an increased number of genetic mutations. Second, they found that birds with red, yellow or orange plumage based on organic pigments called carotenoids, such as Barn Swallows, were much less abundant in contaminated areas than were less colorful species. Carotenoids act as antioxidants.
Additionally, bird species that produce large eggs and those that migrate over large distances were also very scarce. Further, the researchers noted that some bird populations are apparently sustained only because of continuous migration into the disaster area, that the impact of radiation on those species may be to prevent the establishment of self-sustaining populations.
The reason? The affected bird species had reduced levels of antioxidants. In short, antioxidants are molecules that protect the cells in of body from potential damage by “soaking up” free radicals, but unfortunately, antioxidants are limited.
Free radicals, on the other hand, are not.
Free radicals are a by-product of many natural metabolic processes and result from exercise, such as migration. Eggs also contain high levels of antioxidants that protect the developing embryo. Additionally, it is known that radiation triggers the production of free radicals, which are reactive compounds that irreversibly damage DNA.
Areas throughout the Chernobyl region show variable levels of radioactive contamination. Some areas had very low levels of radiation, but others were so contaminated that the researchers had to wear protective suits and masks.
“Survival and reproduction is depressed in those areas,” Mousseau reported.
Interestingly, according to previous work that was recently published in April 2007, most nesting birds can apparently detect the higher levels of radiation and preferentially choose nesting sites where levels are lower.
These data have important implications for people as well as for birds. For example, the high level of abnormalities in these birds suggest that radiation is also the culprit in the higher-than-average levels of health issues found in humans living near Chernobyl, which directly contradicts a report published recently by the World Health Organization. This report blamed social stresses for the various ailments.
“Birds don’t drink, birds don’t smoke, and they don’t suffer the same kind of stresses as humans,” Mousseau pointed out.
Mousseau’s ongoing research focuses on documenting the effects of low-level radiation over large areas, and examining how ecosystems change and adapt after an event such as the Chernobyl nuclear disaster. Bird species are just one group of animals that the scientists are studying in the area.
Mousseau plans to return to Chernobyl to continue studying the bird populations over time.
This research was published online in the Journal of Applied Ecology.
Determinants of interspecific variation in population declines of birds after exposure to radiation at Chernobyl by A. P. Møller and T. A. Mousseau. Journal of Applied Ecology (OnlineEarly Articles). DOI: 10.1111/j.1365-2664.2007.01353.x [free PDF]
Møller, A.P., Mousseau, T.A., de Lope, F., Saino, N. (2007). Elevated frequency of abnormalities in barn swallows from Chernobyl. Biology Letters, 3, 414-417 | doi:10.1098/rsbl.2007.0136 [free PDF]. (image)