Is vinca/perwinkle poison for ducks?

[nurserunner7]

I am fencing off an area for my ducks. There is a lot of vinca/periwinkle vines in that area for ground cover. Will this be dangerous to my ducks? Has anyone had any problems with this kind of ground cover? I know it is listed as toxic. I have had chickens but never ducks. Can anyone help with this answer?
Thanks so very much for assist with this new duck person...

 

[JJRS]

I know 3 ornamental breeders who have it in their aviaries and the ducks/geese don't touch it.