Those intruding on their territory, including large wildfowl, land mammals and people, may be warded off with an aggressively fast swimming approach, often accompanied with hissing and busking, which is a threat display where the swans neck is curved back and its wings are half raised.
In this case in Chicago, he says, it's understandable that someone in a river with their clothes and shoes on was unable to overpower a swan and swim to shore.
It is Europe's largest thermal power plant and its biggest polluter, emitting the equivalent of close to 39 million tonnes of CO2 last year, a rise of 31% from 2010 thanks to the commissioning of a new unit in September
It burns lignite, also known as brown coal, the cheapest fossil fuel, which produces energy at half the cost of hard coal and a quarter the cost of natural gas.
RisinRising temperatures in Antarctica are having an impact on the continent's many colonies of penguins - some are flourishing while others have undergone a significant population fall.
Among the innovators, Australian airline Qantas says its technology can track luggage anywhere in the world while a new check-in process could take less than a minute.
"I knew the number of passengers and I made a brief estimate of what it would cost to send them from Athens to the north of Greece and I decided it was quite obvious it would be cheaper to send them there by taxi rather than train."
China experienced its biggest political scandal in a generation earlier this year when politician Bo Xilai was sacked and his wife found guilty of murdering a British businessman
Abdollah Hemat, spokesman for the governor of Uruzgan, told the Afghan Islamic Press news agency that the dead man was a civilian and not an employee of the government.
No group said it had carried out the attack, but Mr Hemat blamed "the enemies of Afghanistan", a term used by Afghan officials to refer to Taliban insurgents.
