My sister had 1 mallard & 1 female duck of some kind. They were around 5 months old. She wasn’t putting them up at night, but has about a 5 foot fence. 2 days ago the female was gone & last night the male. No signs of any predator nor any evidence of attack. Could they have flown away or more likely they were taken? Just wanting thoughts from those of you who might have insight. Thanks!