Hummingbird babies hatch at Franklin Park Zoo

By Melissa M. Werthmann, Globe Correspondent

A hummingbird has zookeepers’ hearts all aflutter at the Franklin Park Zoo this summer.

Bluebell, the zoo’s only female Costa’s hummingbird, is a proud mom of two tiny chicks, which hatched Friday and Sunday, zoo staff said in a statement.

“This birth is a real reason to celebrate,” Frederick Beall, general curator for Zoo New England, said. “As with any new birth or hatch, we are closely monitoring the mother and babies and are hopeful that the chicks will thrive.”

Bluebell arrived at the zoo last year, at just over one year old. She can be seen hovering inside Butterfly Landing, where she resides seasonally with two male hummingbirds, staff said.

Beall said he believes these are Bluebell’s first chicks, as well as the first pair of Costa’s hummingbirds to be born at the zoo.

This is the second set of eggs Bluebell has laid this summer. Unfortunately, the clutch of eggs she laid in late June did not hatch, staff said.

Staff members were surprised to see that Bluebell had built another nest, which she constructed using plant fibers, animal hairs, feathers, and spider webs — with no help from her other half. Staff said that since hummingbirds are solitary creatures and have no pair bond, Bluebell was solely responsible for the creation and maintenance of her nest.

The birds typically lay two eggs, which measure about half an inch by one-third of an inch — small enough that two could fit on a dime — and take about two weeks to hatch, staff said. The chicks measure about half an inch when they hatch; at three weeks, the birds are full-grown and ready to fly.

Beall said zoo staff will not be able to tell the sex of the hatchlings until they are four to six months old, which is the time male hummingbirds start developing brightly colored plumage to impress females.

Costa’s hummingbirds are the second smallest hummingbirds in North America and are predominantly found in Mexico and the western United States, staff said. All three of the zoo’s Costa’s hummingbirds were born at West Coast zoos.

The staff was especially excited about the new hatchlings because it is rare for the birds to breed in captivity.

“We were thrilled when the female built a nest earlier this summer and to now have chicks is just amazing,” Beall said.

Melissa Werthmann can be reached at melissa.werthmann@globe.com.