Rats can be brazen little shi** when they get used to their surroundings. However, I'd expect mother duck to at least put a fight up if it was rats. Same with any terrestrial predator really. There would be a lot of commotion, and ducks are far from quiet when predators are around. I'd suggest an aerial threat to be honest, sparrowhawk, buzzards, even crows could be partial to a duckling. I presume there's little evidence of attack? Again, that would suggest whatever it is takes them immediately. Stoats, rats, minx etc would all kill before taking them away.
Could it possibly be a sneaky cat hanging around?
Is it possible to set up CCTV that just records constantly? Cheap kits can be had for around £30 these days.
Giving power to politicians is like giving whiskey and car keys to a teenage boy - P. J. O'Rourke (thanks Jessie)
It's amazing that people can believe everything is predestined but they still look both ways when crossing the road - Stephen Hawking
1 Wife, 3 children, 1 Staffie Bitch (RIP Marley), 1 Chi-Chi, 1 Tuxedo Cat, 1 part Maine Coon cat, male bearded dragon, Horsefield Tortoise, 2 White Silkies, 1 Frizzle Pekin, 1 CLB, 1 Appenzeller Spitzhauben Cockerel, 1 blue laced Wyandotte, 3 Appenzeller x Wynadotte pullets, 1 Call drake, 3 khaki Campbell ducks, 4 (2 male 2 female?) Aylesbury x Campbells, a breeding colony of Dubia cockroaches.
And a lot of Ibuprofen.