Just on rereading this, this comment sounds a little condescending - it wasn't meant to be. I was just being a little absurd and should have bunged in a light-hearted smiley, or something.
I only have a 2nd edition Nat.Geo.Soc field guide for North America, so it's comments on Muscovy is probably out of date, "Recent sightings along the lower Rio Grande are believed to be wild birds from Mexico".
"Recent" in this case being 1987 when it was published.
Perhaps the Audubon Society in near you might be interested in this sighting as well as us

?