Marsh warblers are one of the species affectedBirds living around the site of the Chernobyl nuclear accident have 5% smaller brains, an effect directly linked to lingering background radiation. The finding comes from a study of 550 birds belonging to 48 different species living in the region, published in the journal PLoS One. Brain size was significantly smaller in yearlings compared with older birds. Smaller brain sizes are thought to be linked to reduced cognitive ability. BBC