Energy

Each night, a Hummingbird enters torpor: its heart slows from up to 1,200 bpm to under 50, body temperature drops from 40°C to ~10°C, and metabolism falls 95%. Without this near-death energy saving it could starve before dawn; wing-muscle tremors wake it before sunrise.

The Kardashev Scale measures a civilization's advancement by energy usage. Type I harnesses all energy reaching its planet; Type II, all from its star; Type III, all from its galaxy. Humanity currently sits at about 0.7 on this scale.