I'd say it'd be more apocalyptic (as per Dr. Venkman's «dogs and cats, living together» dictum) if the animals were migrating to environments * more * likely to result in their
extinction;) Having said that, I acknowledge that a common view is that humanity is doing exactly that — not a physical migration, but an enforced anthropogenic man - handling of the entire biosphere
towards a bad neighborhood in Earth's «state space», where we risk being stabbed by shadowy tipping points, mugged by run - away processes and distressed at the sight of an anoxic ocean vomiting over the
local fauna.