For nearly a year, a series of names have buzzed around my brain like so many tiny birds: Cactus. Wasabi. Larry Bird. How are they? What are they doing? Where are they? Spend any amount of time with Sally Aitken’s delicate, immensely touching documentary “Every Little Thing,” and you’ll fall to the same obsessions and curiosities.

In Aitken’s doc, you’ll meet Cactus, Wasabi, Larry Bird, and many more. You’ll meet the people who, often quite unexpectedly, rescue these tiny hummingbirds from various kind of peril. And you’ll meet bonafide real-life hero Terry Masear, who has turned her Los Angeles home into a hummingbird haven for all sorts of tiny charges.

Aitken doesn’t skimp on incredible, immersive hummingbird footage, all bright colors and fast-flapping wings, quick little tails, shining pinprick eyes. Hummingbirds are so delicate, so feather-light, so special, it’s easy to see...