We housed our ducklings in their newly built desres 3 weeks ago (having weaned them off the indoors/heatlamp stage) & kept them in a covered run (sorry buzzards no dinners for you here).
We let them free-run after a week & have had to chase/cajoule/ bribe/herd the little darlings in EVERY night since

Weyhey - they put themselves to bed tonight, the little angels
