A Bluebird Trail in Colorado

By Mary Kiesling

It’s spring. The Mountain Bluebirds are arriving. My volunteer time is starting for another season of monitoring nesting boxes.

Loading the car with an extra box, tools (including a drill), notebook, snacks and water, I am ready to go.

After leaving Greeley, two more volunteers are picked up. The drive up Cameron Pass is beautiful with blue skies. We are heading to North Park area of Colorado. Adding one more volunteer to our group, we are headed to Walden.

Just west of Walden, we begin our Bluebird Trail route to monitor 47 wooden nesting boxes that are being used this year. These boxes have been placed throughout Jackson County.

We are into our 23rd year of monitoring the boxes which began as a cooperative project with the Colorado Division of Wildlife (now Colorado Parks and Wildlife) and the Denver Audubon Society. These boxes are monitored four to five times during the season. The route we travel is about 200 miles, most of it on dirt roads.

Arriving at our first box which is fastened onto a wooden fence post, we are out of the car, anxious to look inside the box. When approaching each box, we knock gently on the side of it. It’s a way of letting any occupant know that the front of the box is going to be opened. This gives the adult bird a chance to leave the box if it wants to. Leaving the box makes it easier for us to look inside to view its contents. The majority of the nesting boxes are located four to five feet high fastened onto wooden fence posts. When a nesting box is high enough that it is difficult to view the inside, we use a small hand mirror held inside the box to show what and how many are in the box. Property owners had previously been asked for permission to mount the boxes. Most of these boxes are around water of some type (lake, stream, field irrigation).

Lifting up the front panel of the box we peer in to see a very neat grass nest. The Mountain Bluebirds have claimed this box. Sometimes a Tree Swallow will claim a box for its nest which is similar to the Bluebird’s nest. The difference is that the Swallow nest is deeper than the Bluebird’s and is completely lined with feathers.

After viewing the nest, the front of the box is closed and secured. Back in the car, a simple report form is filled out. Now we drive on to check Box #2 in this area.

A usual sequence of our five trips would be to observe: 1) nest construction; 2) egg count; 3) counting of young; 4) record the number of birds fledged; and 5) cleaning out of the box so that it is ready for the next year.

Depending upon the previous winter’s weather, when we open a box on our first trip in late May, we will sometimes find that a complete nest has been constructed and already contains Mountain Bluebird eggs. Wonderful to count them and record the number. A long-term goal of the Bluebird Trail Project is to gather monitoring data from Colorado. At the end of the season the numbers will be sent to the Cornell Laboratory of Ornithology.

When arriving in the spring from the south, Mountain Bluebirds seem as blue as the sky. They migrate in flocks of usually more than 100. The size of bluebirds is about 6-7” in length. They are smaller than a robin and the bluebird’s eyes, bill, and legs are black. Sometimes their early spring arrival mixes with late spring snowstorms which can prove to be fatal for many of these beautiful birds. The males have the sky blue color while the females are mostly gray in appearance with bright markings on wings and tail.

Bluebirds are early migrants. Males arrive several weeks ahead of the females. When females do arrive, the male shows her several nest sites, and she decides which one they will use. They like a fairly open habitat of large meadows, sage lands, and some trees. They may nest in holes other birds such as woodpeckers have made in the trees. Wooden boxes are a good replacement for the nest sites lost in natural habitat and are best placed at the edge of a clearing. The nice thing about the nest boxes is that they provide a somewhat weather-proof cavity. All three species of bluebirds (mountain, eastern, western) are cavity dwellers choosing a site that has been created and used previously by another bird. With the loss of habitat in some areas, putting up a nesting box is a good thing to do.

Nests are usually composed of fine grasses and are shallow. The female does most of the nest building, but the male does bring material to the site occasionally. The nests are very neat and clean. The female will lay 4-6 pale blue eggs. One egg is laid early every morning until the clutch is complete, and then the incubation begins. The female does most of the incubating since she has a brood patch and the male does not.

Once the eggs are laid, incubation periods are about 13-15 days with the actual fledging (leaving the nest) being around 19-20 days.

Bluebirds will mainly eat insects like spiders, grasshoppers, ground beetles, crickets, caterpillars, etc. in short vegetation. Being primarily an insect-eater, the mountain bluebird may launch from its perch quickly to the ground to grab a meal. Both parents will be feeding the young once they have hatched. The bluebird’s enemies include squirrels, raccoons, snakes, weasels and sometimes cats. Occasionally another larger bird will try to enlarge the opening to the nest box in order to get inside for its meal. In this case we put a new door patch on the front of the box.

Bluebirds tend to be very tolerant of humans. We are glad for that since we are at several times during the spring/summer seasons peering into their cozy homes and using gentle voices to talk to them.

Being volunteers with a program, it is always so interesting to see the various stages of growth once the eggs hatch. The chick uses its egg tooth near the tip of its beak to help break out of the shell. The young are born naked, featherless, with stubs for wings, yellow beaks, and large unopened eyes that you can see through their transparent skin.

During the first 2-4 days, the feathers develop under the skin and the chick is beginning to show its fuzzy down. The mouths of the young seem huge compared to the size of the rest of their body. At 5-7 days the feathers begin to break through the skin and the eyes begin to open. Days 8-11 show rapid growth and feather development. The young birds’ eyes are open completely now.

With 47 nesting boxes to monitor each trip we make, it is always a surprise and interesting to see the various stages of nest building, egg laying, hatching, and growth of the young. Being in a volunteer program provides wonderful opportunities for the sights and sounds of the environment. We definitely do enjoy being a part of this project.