Moonlarks, or "Suldreens" in the Enlightened Language, are extremely rare birds. Moonlarks lay their eggs in the oceans and allow for the tide to carry the eggs away. Baby moonlarks must fend for themselves in the world without a family. A parent is, however, always secretly watching out for them to make sure they're safe. They sing melodies of guidance or comfort that help the baby moonlarks, as while they are physically alone they are never truly so. Because of this teaching technique of fowl, the Black Swan named Sophie "Project Moonlark". She was tossed out into the sea of humans, other than Mr. Forkle secretly watching her as her next-door neighbor. Alden borrowed two moonlarks from the Sanctuary to study their habits in Book 1: Keeper of the Lost Cities. They live in habitats with water, such as lakes and ponds; Alden used the lake at his home. In Nightfall, Mr. Forkle says the only place that he ever found moonlarks in the wild is Brumevale.
Moonlarks have silver feathers, long legs like a crane, a neck like a swan, and a long tail like peacocks. They are described to be quite beautiful.
Sophie was dubbed Project Moonlark by the Black Swan. When Sophie was a baby, her family thought that she was trying to pronounce her name, but instead of saying Sophie, she said "soybean". That ended up being an annoying nickname throughout the time when she was living with humans. It turns out she was saying "Suldreen" or Moonlark in the Enlightened Language, neither Sophie nor soybean.