Raped!
Aggravated assault
During an unguarded moment, one or more male intruders may force themselves upon the female of an established pair. She protests furiously! But an intruder may succeed in his purpose if he is aggressive enough.
Sperm wars
The male partner rushes in to drive off the perpetrators. The male usually mates with his partner directly after such an assault, in an attempt to supplant the intruding sperm. He does not always succeed: One of ten mallard chicks has a father other than the male of the pair.
