I have just suffered a dog attack at my place which has left me with one solitary duck after the others were killed. As I know they are flock animals, I can get a couple of more ducks locally. Should I introduce them slowly, or just let them get on with it? I'm not sure if they are as aggressive as chickens. ( all ducks, no drakes)
Assuming like the other person has already said, you have dealt with the dog problem and are certain the ducks will be safe you should be fine introducing a couple more girls to your lone girl. In some ways you might be better not getting two females who are already good mates, as that way all three ducks will be on the same footing, rather than 2 vs one. I usually also put new ducks in a run where they can get close to each other with a fence in the way for a day or two before letting them in the same run together. There will probably be a little bit of pecking as they sort out their hierarchy, but most females get along fine after that bit of business is sorted out.
My experience is with mostly mallard type (ie khaki campbell, Pekin, runner and so on) ducks and not muscovy, If you have a muscovy this advice may not apply, though people I know who have muscovies have never mentioned any major issues introducing girls to other girls.
If possible try and get a couple of ducks who are similar in terms of dominance /submissiveness to your lone duck. Or at least try to not get two dominant ducks who are already friends if your lone duck is quite submissive.
Definitely go ahead and get some ducks though, your poor sole survivor will as well as feeling traumatised from what happened to her flock mates, also be feeling very vulnerable and alone right now without other ducks around.