Protecting the bluebird population in Castle Rock originally began with a Boy Scout wanting to earn his Eagle merit badge. Now, it is a thriving program that continues to grow in volunteers and baby bluebirds each year.

Barbara Spagnuolo, Castle Rock's natural resource specialist, said the scout originally placed 18 specially-built nest boxes throughout the community in 2007. Now, there are more than 190 boxes at 32 sites, including schools.

“The ongoing interest in this project is so encouraging,” Spagnuolo said. “People want to see and encourage bluebirds. When we think of bluebirds, we think of color. We think of spring. Especially with the mountain bluebird.”

The Castle Rock program is part of the statewide Colorado Bluebird Project, which operates under the guidance of Denver Audubon. The overall mission is to improve the vitality of bluebird populations throughout Colorado and to inform and educate the public about the importance of bluebirds.

The project is important, Spagnuolo said, because bluebird populations have been impacted for a variety of reasons, including a decrease in natural nesting sites.

Spagnuolo said natural nesting cavities include old trees and wooden fence posts where woodpeckers create small crevices for the bluebird to take up housing. However, these options have been reduced over the years as development clears land and fencing is changed out for metal posts, she said.

Finally, Spagnuolo said one of the main causes of the decreasing bluebird populations is letting domestic housecats outside. Each year, Spagnuolo said an estimated one billion songbirds are lost to cats.

Currently, Spagnuolo said the Castle Rock program is gearing up for the 2021 season, which usually runs between April and August. The start of egg-laying season for bluebirds, Spagnuolo said, may start later depending on late-season snow storms.

Spagnuolo said if bluebirds lay eggs early, it can result in the loss of a lot of baby birds. One season, she said a late storm resulted in the loss of more than 100 eggs.

Spagnuolo said the town relies heavily on volunteers each year. The volunteers go through training before going out to monitor boxes. They are taught what to look for, and it is stressed that they are never to handle the eggs or disturb the nesting birds.

The volunteers are also taught to identify the various bluebird species, and to understand the difference between a swallow and a bluebird. Spagnuolo said swallows have been known to take up residence in the nesting boxes.

Even if the nest, which is designed to fit the bluebird preferences, is taken up by a different bird species, volunteers do not mess with nature. Spagnuolo said other birds are allowed to stay.

The nest box is specifically made to entice a bluebird. The box is essentially an artificial nesting cavity made of pine, redwood or cedar. The boxes are installed in late March, Spagnuolo said, before the bluebird population returns from winter migration.

Through the season, volunteers monitor when eggs are present, count how many actually hatch and after about three weeks, count how many babies leave the nest successfully.

“It is always such a joy to see (the bluebirds) using the next boxes that volunteers are monitoring and maintaining,” Spagnuolo said. “Seeing the bluebirds sitting on top of them is a good feeling.”

Spagnuolo said over the years, Castle Rock has had about 6,700 baby bluebirds successfully leave the nest boxes.

The community as a whole can get involved in the project. Spagnuolo said there are instructions on how to build a bluebird nest on the town's website. She said residents are encouraged to put nests in their own yards to help increase the local bluebird population.

To volunteer, or get the plans to build a nest box, visit the website at www.crgov.com/2028/Colorado-Bluebird-Project.