Northern Prairie Wildlife Research Center
Description and Range
Bluebirds belong to the thrush family, Turidae, whose members are known for their singing ability. The Turidae family is comprised of 19 species including the popular American robin. There are three distinct species of bluebirds; the eastern, western and the mountain bluebird.
In North Dakota, we can observe two of the three bluebird species; the eastern and the mountain bluebird.
The Eastern Bluebird
Male eastern bluebird holding one of thousands of insects it will consume or feed to its family.
The eastern bluebird is found across the entire state of North Dakota but is more common in the central and eastern portion.
The coloration of the eastern bluebird differs somewhat between adult male and female birds. The male is dark blue on the head, back, wings and tail. It is reddish brown from the chin down over the breast. The belly is white. Females are a lighter blueish-gray on the back, wings, head and tail. They also have a lighter reddish color on the breast and are white on the belly. Some females appear almost all brown while others are more similar to the adult male.
Male mountain bluebird perched on an old cedar tree, typical of habitat found in its western North Dakota home.
The mountain bluebird is found primarily in the western one-third of North Dakota. It, however, has been observed in areas further eastward and continues to be lured to some of these locations through placement of nest boxes.
The adult male mountain bluebird is sky blue on top of the head, back, wings, and tail. It is lighter blue from the chin to the belly and gray-white on the lower belly and under the tail. The female is greyish on the head, back, throat, breast and flanks. The wings and tail are sky blue. Mountain bluebirds are slightly larger than Eastern bluebirds.
They measure about five inches in length and have longer wings, which extend about three-fourths the length of the tail when folded.
Both bluebird species feed primarily on insects, crickets, spiders and beetles in the spring and summer. Perches such as fence posts, fence wires or highlines are often utilized to view for unsuspecting insects. If perches are sparce, bluebirds will hover overhead much like a hawk in search of prey. Bluebirds will utilize wild fruits, berries and seeds during the fall to prepare them for their migration south.
Arrival and Territory Establishment
Male bluebirds arrive in North Dakota in March, weather permitting, and begin searching for nesting space. Having found a nesting site, males establish this area as a territory and defend it from other males.
Once a female arrives on the territory, the male will begin a variety of behaviors which will attract a female and tend to call attention to the various nest holes on the territory. For example, the male may repeatedly poke his head in and out of a nest hole or cling to the side of the box and do a wing-wave display, flicking one or bothg wings open at a moderate speed.
Once both birds go into the nest box several times, they are generally considered paired and will likely use that particular nesting site.
An accepting female will begin nest building shortly after they have paired. At this point, the male begins what is termed mate-feeding where he collects food and feeds it to the female. They keep in touch by calls and visual displays as they fly about the territory.
The male follows the female closely as she forages and builds the nest. The male is close by both signaling her when it is safe to fly out of the nest box and to prevent other males from mating with her. Copulation can take place anytime from the beginning of nest building until the start of incubation. It generally takes place close to the nest box and may occur on top of the box itself.
Bluebirds are cavity nesting birds meaning they naturally nest in a hollowed-out area in a dead or dying tree. This is different from other songbirds such as robins and finches that build a cup-shaped nest in the branches of trees or birds like the meadowlark or horned lark that construct nests on the ground.
They are further considered secondary cavity nesters because they cannot excavate their own cavities in tree trunks such as woodpeckers which have heavy bills adapted for heavy pounding.
Today, one of the most utilized nesting locations for bluebirds is the man-made boxes that mimic the natural cavities provided by dead and dying trees. This habitat has been limited throughout the years by removal of old trees thought to be of no benefit to wildlife.
In addition to natural and man-made cavities, bluebirds have also been observed using crevices in rocks and cliffs, drain pipes, mail boxes and old farm machinery.
|Eastern bluebird nest containing three eggs. Both species construct nests of grasses and normally lay 4-6 eggs.|
Nest Building and Incubation
As discussed earlier, the male bluebird takes the lead in exploring habitat and attracting a mate but the female is the one who makes final determination of where the nest is built. This process can be swift or it may take weeks. The time utilized in this effort is usually dependent upon the birds experience and whether they had previously nested in that same location.
Females are in charge of all the actual nest building. At times, the male may carry some nest material but this seems to be a behavior to stimulate the female to nest build and does not amount to much in overall creation of the nest.
A nest normally takes around six days to complete but may be interrupted and begin at a later date. All of this is dependent upon weather and individual bluebird habits. Pairs normally spend less time building nests for their second or third broods.
During egg laying, the female leaves the eggs unattended and begins incubating after the last or second to the last egg is laid. She is also in charge of incubating the eggs by herself. One reason for this is that she develops a brood patch consisting of an area on her breast where feathers are lost and blood vessels increase. This allows her to keep the eggs at the right temperature for development, a task the male could not perform.
During incubation, the female attends to the eggs almost constantly. Eggs are incubated throughout the night and during the day except when she leaves the nest to preen herself or feed. On hot days, eggs may be left for longer periods of time since they maintain adequate temperatures without her help.
While the female incubating, the male may come by and sing or bring food. It may be a signal that no predators are nearby and that she can safely leave the nest. While she is away, the male will remain close by and may even enter the nest box. At night, the male may sit next to the incubating female.
Incubation for both species is about two weeks but can be affected by weather. In cold springs, incubation can actually take somewhat longer if eggs experience periods of cooling.