What are the environmental implications of bringing extinct species back to life? Apply your answer to the case of the Passenger Pigeon

Habitats for many extinct creatures are gone or conditions are perilous. Take the gastric-brooding frog. The species, known for converting its stomach into a uterus and vomiting tadpoles, was driven to extinction in 1983 by chytrid fungal infections. A project to clone the frog managed to get the cells of another frog species to replicate gastric-brooding frog DNA - a promising first step in restoring a gone-too-soon species. Not to mention the hostility other reanimated species might face if their interests run counter to those of humans sharing a habitat