Yea. There's a pretty big difference. The fulvous make like a 2 note squeal/whistle. The black bellies make an off the wall sound.

There's about a 100 of em on some property I train on in grand lake. They're almost tame. I wanna scrape shoot a wad of em for the annual Duck Eve Dinner. But I'm not goin to.

Y'all should see em behind the house.. You can sit on my porch and throw rocks at em as they fly over.
These bad boys when they holler its a long drawn out call.
Not sure which one they are.. Opposite of the ones I posted in the pic lol they have a pink bill almost

Those are black bellies you are seeing at your house

got into um good one day last year....excellent eating duck as well