The slow-motion footage in “Every Little Thing” of hummingbirds captured in flight, or beak deep in a flowering bud or hovering at 50 beats per second are awe-nudging. Director Sally Aitken’s nature documentary comes as a balm in a season aching for uplift. Since 2008, hummingbird sage Terry Masear has run a hotline, answering the calls of strangers who find the iridescently feathered, delicate, surprisingly bold birds wounded or unconscious in their pools, on roadways, laying beneath trees. There have been more that 20,000 calls.

Like pilgrims brimming with fear and hope, Angelenos bring their precious gifts to Masear’s home in the hills of Los Angeles. “It’s delicate, emotional work,” rehabbing these birds, says someone on the radio as the hummingbirds begin their migration to the area where they nest.

As captivating as the documentary’s slow-motion images are (stunning wildlife photography by Ann Johnson Prum), hummingbird lovers know that...