I noticed this a few weeks ago, my ducks who are now around 7 months old, would every now and then repeatedly make funny quack noises like a machine gun (ackackackackack) and move their head to their side like they might put it in their feathers and sleep. Almost like a twitch or something. Is there something wrong with them? They've never left the farm, free range daily, aren't currently laying (haven't layed at all yet!!), are housed by themselves in a duck house. Have had the appropriate shots when hatched. Thoughts?