Eagle is the symbol of observation. The Sioux consider it to be the creature that best symbolizes immense wisdom. It learns from all that it sees. It is the eyes of the all-seeing Wakan Tanka, the Great Spirit, the mysterious unknown entity that created all things. When the Sioux see an eagle flying, they are reminded of Wakan Tanka's observation of their actions — both what they do and what they don't do, both good deeds and bad.
— Ed McGaa, Nature's Way