[advantager]

Left to their own devices, wild mammals have to cross significant human barriers (roads, neighborhoods, fencing, etc.) to repopulate certain natural areas which they have been exterminated from.

Where I live in Southern Arizona, re-population efforts for bighorn sheep have been successful in the mountain ranges near cities (Tucson). Access to these ranges from nearby "naturally" populated areas (50+ mile distances) requires crossing the interstate, fenced in train tracks, ranches, and extensive urban development. Since their extermination from certain areas, this has not happened naturally (and is arguably not possible). I think similar arguments could be made for the Mexican Wolf population in the southwest.

I agree in principle that ecosystems will re-equilibrate on their own, but given the current state of human development certain areas would remain off-limits for various animals without human intervention, maybe leading to certain species or subspecies becoming extinct. I'm no wildlife biologist but would defer to one on this topic.

[ajuc]

European motorways (at least new ones) are built with bridges for animals. Like this:

https://www.crazynauka.pl/wp-content/uploads/2021/06/microso...

And that's in a country with 120 people per square kilometer compared to 36 people per square kilometer in US.

Matter of regulation.

[jeffbee]

America has those too, but they’re enormous and expensive because we’re dumb. https://www.smithsonianmag.com/smart-news/animals-are-using-...

[justincormack]

Same with reintroduction of beavers to the UK, it is an island they won’t get here (unlike some birds). We also need some predators for deer other than humans here.