The Alpine Ibex

The Alpine Ibex (Capra ibex) mingled with Wooly rhinoceros and Mammoth. Today they still inhabit the steep mountains of the European Alps. The wild goat survived Cro-Magnon stone-age hunters. Intensive hunting, especially in the 19th century eradicated many Alpine ibex, except for a few in the Gran Paradiso massif (Valle d'Aosta region, Italy) The region is a protected National Park today.

At present 75% of the ibex offspring die within their first year of their life. (Via it/de) Speculation about their population collapse ranges from high temperatures and sparse grass to poisoned grass. Aircraft engine exhaust gas is thought to settle and accumulate in the snow/ soil that provides the food for the 2.500 remaining herbivores. The young simply collapse exhausted at the beginning of their life.

Images:

Marc, Franz: Steinbock, (Capra ibex) 1913 via Zeno
Brehm Alfred, Brehms Thierleben, Bergsteinbock (Capra pyrenaica) via Zeno

Update:
The first de-extinction "success" was a cloned Pyrenaean ibex: Born with deformed lungs, it lived only 10 minutes. Nautilus Mag 012015