Hummingbirds at rest are one of my all-time favourite subjects.  Ever alert, they are continually raising and relaxing their iridescent feathers.  The smallest turn of the head will release dazzling refracted rays of colour, while the next will turn that fiery gorget into ebony. Their exceedingly high metabolism (the highest of any vertebrate) keeps their little chests heaving rapidly, and the perpetual state of near starvation they exist in from burning off all that fuel means that they must be ever ready to drive competitors away from their precious food supply.

Male Ruby-throated Hummingbird

Hummingbirds burn so much fuel, in fact, that they must put their bodies into hibernation (or, more correctly, nocturnation) every night — a state known as torpor, in which in the heart rate slows, the body temperature drops, and the bird’s metabolism eases to as little as 5% of its daytime rate.  This hypothermic state gets them through to sunup the next morning, when they can once again begin feeding.

Finding so much energy and aggression packed into such a tiny scrap of feathers is part of what makes hummingbirds so much fun to watch.  Although they rarely sit still for long, they do tend to return to the same perch again and again in between feeding sessions or aerial dogfights, so one does get ample opportunity to sketch.