WATCH: David Muir shares milestones of Fort Worth Zoo's Sumatran tiger cubs

The Fort Worth Zoo in Texas has welcomed pair of critically endangered Sumatran tiger cubs — the first in the zoo's history. David Muir shares the milestones they've already reached.

The Fort Worth Zoo in Texas has welcomed pair of critically endangered Sumatran tiger cubs — the first in the zoo's history. David Muir shares the milestones they've already reached.