Bluebird eggs hatch within a period between 24 to 50 hours. Chicks hatch blind and naked.
Both parents take care of the young and feed them with a diet rich in proteins, mostly insects.
Nestlings grow fast and leave the nest in about 16 to 25 days, depending on the region. After they fledge, parents continue taking care of the fledglings for about three weeks until they become independent.
How long does it take for bluebird eggs to hatch?
The incubation period is variable within the Bluebird’s ranging between 11-19 days with an average of 13.5 days. Bluebirds in the warmer southern states have slightly shorter incubation periods than those in colder northern regions.
The female Bluebird starts incubating the eggs on the last or day before last she lays the last egg. She lays one egg every day but does not sit on them.
The female does all the incubation of the eggs. Once the egg hatch, she broods the nestlings continuously until approximately day 5-7 after hatching, when the nestlings begin to have some thermoregulatory control over their body temperature.
The male is always around bringing food to the female while she incubates the eggs. Then, the male also brings food for the brooding female and the nestlings during the first days after hatching.
Hatching begins 1 to 6 hours before the chick emerges completely from the egg.
The female incubates all the eggs for about the same period of time, ensuring that eggs hatch as close to each other as possible, eliminating the size advantage of chicks that hatch first over those that hatch last.
Blind and mostly naked.
Bluebird chicks at hatch are blind and mostly naked with patches of gray down. They weigh approximately 2.4 gr (0.08 oz).
Baby bluebirds are “altricial,” which means that nestlings are entirely dependent on their parents until they become nutritionally independent and can find food for themselves.
Both parents work equally to feed the chicks.
Both parents feed the chicks from day one, but the male does most of the work during the first five days after hatching. As in other birds, chicks open their mouth wide when they sense one of the parents in the cavity.
Studies of the breeding biology of nesting bluebirds indicate that both parents take about the same number of trips in and out of the cavity.
The same studies noted that the female alternates feeding with brooding the young birds during the first week as they cannot regulate their body temperature.
After a week, the young birds can regulate their body temperature, and the female does not have to brood them all the time, although she spends the night with them.
Parents appear to take more feeding trips and be more active during the early morning hours. The feeding continues in the afternoon but not as frequently as in the morning.
Foods fed to nestlings.
The parents bring crickets, spiders, grasshoppers, butterflies, and moth larvae, as well as berries such as raspberry, mulberry, dogwood, cherry, and honeysuckle.
The diet of nestling bluebirds is high in protein, consisting of approximately 68% invertebrates and 32% berries. A high protein diet helps chicks grow as fast as possible and leave the nest soon.
Photo: Festive Coquette/Flickr/CC by 2.0
Four to 5 chicks defecating in a small cavity would make a big mess, but both parents clean up the cavity throughout the day.
As it occurs in many birds, right after chicks are fed, these turn around to present the parent with a fecal sack or pellet. The fecal material is encased in a bag-like gelatinous packet the parent takes with its beak and drops far outside the nest.
When the chicks are very young, parents will eat the fecal sacks, but this practice ends as the chicks get older and are fed various food items.
If one of the chicks dies, one of the parents, when possible, pulls it out of the cavity and drops it outside the nest.
How fast do nestling bluebirds grow?
Bluebird chicks develop fast. After hatching, young bluebirds begin making calls loud enough to be heard when parents arrive with food.
Feathers begin to grow and replace the gray down by day 2. The nestlings open their eyes by days 5 and 6. By day seven, the chicks have short feathers in most of the body’s back and sides. By day 13, chicks are completely feathered.
By day 13 and older, male and female young bluebirds can be told apart based on their plumage color.
Leaving the nest comes next.
As with the onset of the breeding season, the age at which chicks leave the nest varies with latitude.
Bluebirds in northern portions of the species range start nesting later, take slightly longer to hatch, and appear to take a little longer to leave the nest than birds in southern states.
However, the difference is small.
Across the species range, young Bluebirds leave the nest between 16 to 21 days after hatching.
Because all chicks hatch at about the same time, size differences among chicks seldom develop. Chicks of the same age and size leave the nest simultaneously.
Parental care after fledging.
Parents and young bluebirds stay together after fledging for about three weeks.
After leaving the nest, young Bluebirds remain in a relative hide for the first week or so. The parents bring food to the fledglings, which are easily located by their persistent calls.
During the first week after leaving the nest, fledglings still depend entirely on their parents for food. They begin practicing flying from place to place.
After the first week, the young birds begin to follow the parents to more open spaces. The young Bluebirds also start performing the typical sit-wait-and-drop strategy to catch invertebrates.
As fledglings gain experience obtaining their food, the parents feed them less and less.
Once fledglings become nutritionally independent, they take trips further and further from the family unit after about three weeks.
Then, the young bluebirds join flocks of juvenile birds that move about in the region.
Field observations have noted that chicks hatched late in the summer may remain with the parents through the winter.
Overall, the time it takes for young Bluebirds to separate from their parents is variable.
Some fledglings stay in the family’s territory for a long time, while others join flocks of juvenile birds and leave the family unit in about three weeks.
Photo: Wendy /Flickr/CC by 2.0
In the event that one of the parents dies, what will happen to the eggs or nestlings?
The effect on the eggs or nestlings varies depending on when and whether the male or the female goes missing. This is because the male does not incubate the eggs nor brood the young.
Disappearance when the pair has eggs in the nest
When one of the parent bluebirds dies or disappears during the egg-incubating period, the nest fails, and the remaining parent is likely to find a new mate and start another nesting attempt. The male does not incubate eggs, and the female could not incubate, brood, and feed the young without the male bringing food.
Disappearance when the pair has nestlings
When a parent dies or disappears when they have nestlings, the possible outcome depends on the age of the young bluebirds.
Generally, the remaining parent will try to get a replacement mate to help raise the brood.
Possible outcomes include:
- If the female disappears when the nestlings are less than 7-8 days old, the nestlings are likley to die because they are unable to thermoregulate their body temperature. While the male will continue feeding them, he does brood them at all. Ifthe female disappears after the 8-12 day, the nestling do not need brooding and the male alone is likely to raise the brood on his own.
- If the male disappears when the nestlings are less than 7-8 days old or older, the female may be able to raise them alone, although she could fail.
Both the widow male or female can enlist the help of a new partner that helps them raise the young. The new partner’s interest is acquiring a territory and having the next brood with parent they are helping. Partner helpers do help but not as energetically as they woudl if the nestlings were theirs.
Helping a widow raise his/her young is a way for “floaters” to acquire a territory. A floater is an adult bluebird ready to breed but does not have a mate or territory.
Older siblings may help parents raising the new brood.
Another observation of these studies was that young birds of the previous brood, still in the parents’ territory, may help feed their younger siblings.
This behavior appears not to be common and happens more often in certain habitat types and conditions than in others. The actual help older fledglings provide is also in doubt. It may be that young birds do this as a manner of practicing for when they become parents.
If one of the parents disappears and older fledgling are around, they are likely to help raise their younger siblings.
- Eastern Bluebird, Life History. All About Birds. The Cornell Lab of Ornithology.
- Gill, Frank (1995). Ornithology. New York: W.H. Freeman.
- Sialis Online. Bluebirds.
- The Birds of the World Online. Eastern Bluebird (Sialia sialis). Cornell Lab of Ornithology, Ithaca, New York.