I've just come across an interesting article published in PLoS ONE (An interactive open-access journal for the communication of all peer-reviewed scientific and medical research), found via the BBC website. This paper (Moller, A.P. et al. 2011) has concluded that low dose (background) radiation can have significant effects on normal brain development as reflected by brain size and therefore potentially cognitive ability. A summary of the report follows (a mix from the actual report and the BBC Article - see foot of article for references).
The findings come from a study in Chernobyl, Ukraine where 546 birds were captured in mist nets from 8 different sites. 4 sites were within approximately 5 km of the power plant and the other 4 between approximately 25 and 50 km from the power plant. The survey was undertaken during the 2010 breeding season.
Ringing sites (*), background radiation levels and power plant location, Chernobyl, Ukraine [Source Moller, A.P. et al. 2011]
In April 1986, reactor number four at the Chernobyl Nuclear Power Plant exploded. After the accident, traces of radioactive deposits were found in nearly every country in the Northern Hemisphere. An exclusion zone has since been set up around the site of the accident, however scientists have been allowed inside to gauge the impact the radiation has had on the ecology of the region.
Nuclear reactor number four after the explosion.
Last year a report was published detailing the results of the largest wildlife census of its kind conducted in Chernobyl - which revealed that mammals and insects are declining in the exclusion zone surrounding the nuclear power plant.
For this study of the birds, background radiation levels were recorded in the field and correlated with the Ministry of Emergencies, Ukraine. Morphological measurements were recorded in the form of wing length, keel length, bill length, width and height and tarsus length. Brain and head size were recorded. Head length (tip of bill to back of head), maximum head width at back of head, maximum head height. Head volume was subsequently estimated. Brain mass was obtained from literature and birds were aged and sexed where possible.
The results from the sample showed that head volume decreased significantly with increasing radiation level, varying among species and with respect to body mass and keel length. After accounting for the effect of difference amongst species, there was a reduction in mean brain volume of 5% across background radiation levels. Males had relatively larger brains than females.
Crested Tit © Luc Viator 2009
When aged birds were analysed there was found to be significant effects of both radiation and age, with yearlings having smaller head volumes than older individuals. That suggests that many bird embryos did not survive at all, due the negative effects of their developing brain.
Stressed birds are able to change the size of some of their organs in order to tough out difficult environmental conditions. For example, migrating birds that have travelled long distances often shrink certain organs as they use up energy, but the brain is the last organ to be sacrificed in this way. That suggests the background radiation could be having an even more pronounced effect on other organs within the birds.
House Martin (© Unknown)
It is unclear exactly what mechanism is shrinking the birds' brains. High levels of background radiation cause animals oxidative stress, where they have to use antioxidants in their bodies to fight its ill effects. That leaves animals exposed to radiation severely depleted of antioxidants, and the reduced brain size may be a result of this depletion.
Alternatively, radiation could cause developmental errors in the way the brain grows. However, if that were the case, pronounced changes to the size and shape of other parts of the birds' bodies would be expected.
Another possibility is that the birds are developing less well as there is less invertebrate prey for them to eat. However there are no known examples of the brains of a wild animal shrinking due to a lack of food.
An interesting article and it will be interesting to see how things develop over the following years as monitoring continues. For info, the species recorded included: Great Reed Warbler, Marsh Warbler, Reed Warbler, Long-tailed Tit, Tree Pipit, Nightjar, Greenfinch, Siskin, Treecreeper, Hawfinch, House Martin, White-backed Woodpecker, Great Spotted Woodpecker, Lesser Spotted Woodpecker, Yellowhammer, Robin, Red-breasted Flycatcher, Chaffinch, Jay, Icterine Warbler, Barn Swallow, Wryneck, Red-backed Shrike, River Warbler, Woodlark, Thrush Nightingale, White Wagtail, Golden Oriole, Blue Tit, Crested Tit, Great Tit, Willow Tit, Marsh Tit, Black Redstart, Common Redstart, Chiffchaff, Wood Warbler, Willow Warbler, Nuthatch, Blackcap, Garden Warbler, Whitethroat, Barred Warbler, Wren, Blackbird, Song Thrush, Mistle Thrush and Hoopoe.
Møller AP, Bonisoli-Alquati A, Rudolfsen G, Mousseau TA (2011) Chernobyl Birds Have Smaller Brains. PLoS ONE 6(2): e16862. doi:10.1371/journal.pone.0016862
BBC News Article