Meanwhile, here in Washington, Lafayette Square was overrun by Sciurus carolinensis, the Eastern gray squirrel, a shakedown artist as aggressive as any three-card monte hustler.

The researchers concluded that the familiar gray tree squirrels, Sciurus carolinensis, have dichromatic color vision.

The Eastern gray tree squirrel, or Sciurus carolinensis, has been so spectacularly successful that it is often considered a pest.