Filmmaker Sally Aitken observes Terry Masear’s efforts to rehabilitate wounded hummingbirds, mixing stunning slow-motion footage of the creatures with insights into a caregiver with scars of her own.

Hummingbirds are described as “sweet warriors” by Terry Masear, a hummingbird rehabber in Los Angeles. She runs a center for the tiny, injured birds, and explains that while the smallest birds in the ...