In Russia, it was revealed that the fauna of Siberia is becoming more southern due to climate change. Global warming will allow tropical species from the Atlantic to colonize the Mediterranean Sea. Global warming is making some species of marine animals more susceptible to the spread of diseases such as avian influenza due to the animals congregating in breeding and feeding areas or changing migration patterns. Some researchers are concerned that current rates of warming could make oceans as warm and acidic as they were during the end of the Permian extinction, 250 million years ago, when up to 90 percent of marine species died out.