Read this article and research is showing mallards are getting more of the domesticated genes. Sounds like weather may not be the only reason why mallards are migrating less often. Many other issues as well that could only make it worse.
“Researchers are discovering that game farm mallards have polluted the gene pool of wild mallards and are now producing a less viable product”
“domestic hens are bad mothers. They’re poor at selecting nesting sites, poor breeders, and just poor at survival in general.”
“It’s obvious these ducks don’t go anywhere. They aren’t programmed to. Unlike wild mallards, they live, breed, and die in the same place.”
https://www.hardcorewaterfowl.com/where-have-all-the-mallards-gone/