In the interior the whistling swan is common, and numerous varieties of ducks are found in the lakes.
Their nesting habits and eggs are the same as those of the whistling swan.
The whistling swan being more of a northern bird, rarely migrating as far south as central California.
The whistling swan yet remains in fair numbers, but it is to be feared that soon it will go as the trumpeter has gone.
At the same time the arctic grouse, the whistling swan, and other northern birds entered the region of the Rhine and the Danube.