Feral chicken are known in several places. They can be pretty successful and have been signaled as threats to ecosystems and crops in archipelagos like Hawaii and Bermuda. But I’ve thinking about Brasil: Given the sheer amount of chicken being bread there, the presence of the Amazon rainforest, which has a similar climate to whence jungle fowls, the chicken’s ancestors come; and its already fragilized ecosystem, isn’t there a specific risk there ? So far, I’ve seen no South American country listed as famous for feral chicken presence . But hypothetically, if a few millions of fowls escaped a massive Brasilian farm and swarmed the Amazon; what could happen ? Would they quickly die off, due to having lost adaptations to wildlife, having an insufficient ratio of roosters and facing many predators ? Would they outcompete one or two local bird species and steal their niche, but otherwise fit fine in the food chain without further disrupting the ecosystem? Or would it spell a great ecological catastrophy ?
Yeah, you might be right, byt just to feed the debate I’ll take the defense of the chicken :
Their sheer number is a big factor : There can be hundreds of thousands in a single farm. Even if tens of thousands die on the first days, the next morning, the survivors will be less fat and more alert.
Red junglefowls are quite adept at living in a rainforest environment despite being nearly flightless and living close to many predators. Their strategy of being diurnal and hiding in the trees at night to avoid mostly nocturnal predators works pretty well and many Amazon predators are noxturnal as well. Mass farm chicken might be too fat at first, but it shouldn’t last too long and feral chicken are known to quickly recover their instincts and start brooding in trees.
Tinamus while very var from chicken classification-wise (and closer to ostriches), fill a very similar niche and have a similar lifestyle to jungle fowls, also being very poor flyers. This proves that this type of lifestyle can also work in the Amazon. And with tinamu populations being destabilized by deforestation, and chicken being more adapted to a variety of lifestyles, they could outcompete them and steal their niche.
Just for the scorpion part : Chicken rarely encounrer scorpions due to these being nocturnal. And when they do, it’s a pretty even match : The scorpions might poison them, but the feathers make it harder and the chicken might eat the scorpion first. Source
Something that might come up in a commercial farm escape is debeaking. They cut the end off the beak to stop them fighting in crowded conditions and that will decrease their chances to defend themselves in the wild.