Springtime: Nature's Newness of Life

I don't see how people can look around them in springtime and not see the intrinsic value of life. A few days ago, while walking down the stairs to morning Mass, I noticed some twigs stacked together on top of one of the window's hinges outside the seminary building, and as the day went on, more and more twigs were put together, forming a nest.

Mourning Dove on Nest

A few days later (yesterday, in the afternoon, to be precise), an egg had found its way to the nest. There is now a mourning dove perched atop the egg (and she is very protective of that egg!), keeping it warm and guarding it from ouside intruders. She was scared when I approached to take a picture, but would not budge, because she knew (it was somehow intrinsic to her nature) that that egg was the beginning of a baby bird's life.

Obviously, birds do not have a human nature, and, as such, don't have all the rights a human would be given (also, of course, mourning doves are among the dumbest of birds, in my humble opinion, so that can't help at all ;-). But how can someone not see how nature itself places such a great value upon life? Someone may give the example, to counter mine, of a fish laying hundreds of eggs, many of which do not have the chance to develop into baby fish, or of some other animal who doesn't stay with her eggs, but leaves them 'to the elements.' But in all these cases, it is still true that it is a natural and intrinsic desire for animals to preserve life and their own species, especially at such an early stage.

Why is it we humans must always try going against what we know to be true?

Mourning Dove Egg in Nest