Maybe the melting ice caps unleashed this poor bird from near torturous captivity in a cave under one of the shelves. It became entrapped just before the previous ice age (man made of course) by human hunters with big guns & ripping flesh on their mind. The poor nature critter was forced to flee the hordes of humans & took, what it believed to be, temporary shelter. That escape pod became its interminable prison as the hole in the ozone, from man made fires, opened up & flash froze the terrain, planet wide. Fortunately, the bird, obviously smarter than man, was able to tunnel to a nearby larger cave which had, fortunately for this narration, 3 females & another male.
Understanding their plight, they made a non-agression pact, with hopes of furthering their species until one day, they would be free, once again to freely & peaceably roam the earths sky without a care, enhancing the beauty of this thing we call Earth.
or,
We aren't as smart as we think we are.