It may be wrong but my assumption is that the birds will really be into the thin skinned seedless muscadine varieties. I had that problem with both the unseeded and seeded table bunch grapes that were thin skinned. That and Pierce’s disease caused me to switch to muscadines which fixed that. Seems that the birds will ignore the tougher skin grapes.
Feathered rats.
Birds are not much of an issue for me. Raccoons are able to eat a vine full of fruit overnight. They are equal opportunity muscadine harvesters. They don’t care what variety as long as they get a full belly.
The birds like my black varieties over the bronze ones. The possums like them all, but they spit the skins out.
My local birds must be made of sterner stuff than the birds of some others. They will strip thick, tough skinned muscadines eat the pulp and drop the skins very readily as will the coons and possums. About the only vermin that thick skin helps against locally is the wasps and hornets. Those will eat a lot of thin skinned bunch grapes in some seasons, but very little damage on the thick skinned varieties/muscadines.
Do muscadine seeds vary in hardness. I find the varieties i’ve gotten from the grocery store perfectly edable, but a little bitter.
Vitis munsoniana, a type of wild muscadine, has much smaller seeds that are more easily crunched up. Of course, it’s a wild type, and the fruit is very small as well . In general, most cultivated, seeded muscadines have large, hard, bitter seeds. Probably not enough variation to be meaningful. Most modern cultivated muscadines are closely related and share a lot of similar characteristics.