It is a teleological phrase. There is a purpose, an end, for every thing created. And there is also an end, as in a finishing point, for everything.
God created the earth, the plants, the animals, and saw that they were good, and then He commanded that they fulfill the measure of their creation. So the fish of the sea, the birds of the air, the cattle of the field, and all creeping things upon the face of the earth are here for a reason. At some point, when the imperative for which they were created has been satisfied, they no longer need be.
If all things were created for humankind, to delight the eye and gladden the heart, to give us fruit, sustenance from their flesh, then we are the measurers of creation. We judge and use, quantify and give things purpose based on their utility to us. Some of us are less practical and elevate the aesthetic qualities and even assign intrinsic value to those creatures and places, that although created by the hand of God, appear useless to our grasping little demands.
I’d assumed for years that for an animal to “fulfill the measure of its creation” meant that the critter was able to live its life. To obtain food and shelter and reproduce. To do what it does, and what it does is what it was meant to do. But the finiteness of a measured thing has forced me to think in other ways about this phrase. Perhaps a species’ creation is measured not at its inception, by God, or during its existence by its own being or in relation to and by humanity, but by its final end. The passenger pigeon’s days have at last been numbered. It’s creation is ended, finally measured.
Did that gregarious bird fulfill the measure of its creation? Did we artificially shorten that measure? I fear that while those created things are still good in the sight of God, we as measurers, the ones who individually use and collectively cause the ends of these created things, may not be judged to be as profitable servants, as diligent measurers, as is implicit in our divine charge have righteous dominion. As our actions cause extinctions, we find there is less creation to be measured, and that diminishes us all.