As far as I know, no animal can starve. I have many pens in different locations, some older, no mass extinction yet
what DOES happen is, that some animals clip out of the pen and then get killed, i have double walls for that.
or that mobs are spawning nearby and kill your animals
if there is loot they got killed
if there is not the maybe clipped out
also oozer aoe dmg kills through thick walls