Mute swans (Cygnus olor) swimming along the shore of Lake Ontario, Canada on a frigid day. These birds may stand over 1.3 meters high and weight more than 15 kg., making them some of the heaviest flying birds. They are native to Europe and were introduced to the US in the late 1800s. Some swans live in colonies of over 100 pairs. Mute swans have been know to attack people who enter their territory or threaten their cygnets. They are considered an invasive species in North America and there are efforts in many places to have them eradicated to protect native species.