it takes three to four years for the mountain yellow-legged frog of the Sierra Nevada to reach adulthood, and so they are

it takes the mountain yellow-legged frog of the Sierra Nevada three to four years until it reaches adulthood, and therefore it is

in the Sierra Nevada, mountain yellow-legged tree frogs take three to four years to reach adulthood, thus being

mountain yellow-legged frogs of the Sierra Nevada take three to four years until they reach adulthood, thus

mountain yellow-legged frogs of the Sierra Nevada take three to four years to reach adulthood, and so they are