I wouldn't necessarily agree with that. Normally this is true, but if Wobbles was hatched without any other ducks around, he could have imprinted as a person. This would mean he would consider Amykins a female and might be very aggressive toward another male. Whereas Pancake would have at least seen Wobbles while growing up and would imprint with Amykins as "mom", but would know he was a duck and would know there were no females around. If Wobbles was paired with a female, if he imprinted as a person, he might not show normal interests in her, but would enjoy the companionship, and if he imprinted as a duck with Amykins just as "mom" all would be normal - either way, no harm.