Colorado has reported its first litter of gray wolf pups in 80 years, a major milestone in the US state's efforts to reintroduce the iconic species even as it stands imperiled in other parts of the country.

Between June 4 and June 8, a state biologist and a wildlife manager independently reported visual confirmation that "John" and "Jane," known collared wolves, were seen with three young.

The observations were made at dusk or dawn from a distance of around two miles from the den site, so as not to interfere with the pack.

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