On a misty morning in late April, at the Indian Peak Ranch in Mariposa, Calif., Barbara and Duane Robinson band hummingbirds with the help of volunteer Susan Robinson (no relation). The ranch sits in the foothills of the Sierra Nevada, 30 miles from Yosemite National Park. The damp morning air is filled with squeaks and the buzz of miniature wings. Hummers flit in and out of a large blue oak that rises above an expansive deck with a view of lush rolling hills of oak and pine woodland.

Indian Peak Ranch is on a migration route, and about four times more hummingbirds have been banded here than at any other HMN site. Barbara Robinson has banded seven species: Anna's and black-chinned, the most common locally along with rufous, Allen's, Calliope and Costa's, plus one broad-tailed hummingbird. Most of these species are migrating through or breeding in the area, but the Anna's are a special case. Barbara believes that the ranch hosts four separate populations: one lives here year round, another breeds here, the third winters here and the last group is migrating through. Her hypothesis is based on recapture data. About 45 percent of the birds trapped here are recaptures, the highest rate in the HMN. Barbara has caught one female Anna's 35 times over eight years. Indian Peak Ranch is no longer an HMN site, but Barbara and scientist Holly Ernest are working together to determine if her hypothesis about the four populations of Anna's is correct.

As she examines a female Calliope hummingbird, Barbara recites the measurements and observations for Susan to record. She carefully pulls a feather from the breast, and Susan puts it in a small manila envelope. Barbara will send the feathers she collects today to Ernest for her genetic work. She wraps the bird in a cloth and places it on the scale, which registers 2.6 grams. "They weigh the same as a penny," Barbara says. "They're sooo little." Susan picks up the tiny bird, removes the wrap, and sticks its long bill into the feeder. The bird immediately starts to drink, its throat moving as it swallows the sweet liquid. She turns to an observer. "Do you want to release this one? Put your hand out flat." She gently lays the bird on the woman's palm; with a brush of wings, it's gone.

This story was funded with reader donations to the High Country News Research Fund.