Understanding Female Eastern Bluebirds: Traits & Habits

What Does a Female Bluebird Look Like?

Distinguishing Male and Female Bluebirds

Male Bluebird Photo

Female Bluebird Photo

What does a bluebird sound like?

What Are the Habits and Characteristics of Female Bluebirds?

Where Can Female Eastern Bluebirds Be Commonly Found in the US?

Do Male and Female Bluebirds Nest Together

Monogamy and Sexual Diversity of Bluebirds

During the nesting and breeding season, bluebird pairs work well together and are attentive to the needs of their young and to each other. Occasionally, you might even see them waving their wings to each other as a signal. Year after year, many bluebird landlords see the same pairs returning to nest sites. It would seem that when bluebirds mate, they mate for life, but that isn't exactly true. While bluebirds often socially mate for life, having the same nesting partners each year, they don't always sexually mate for life.

Instead, bluebirds sometimes engage with others who they aren't socially bonded to. Molecular testing has even confirmed that some bluebird nestlings are from other males. The percentage of this occurring, however, varies widely between studies. To give it a little perspective, in a given clutch or set of eggs, sometimes one or more of the eggs is not from the bonded male but from another neighboring male, and these are called extra-pair eggs.

While bluebirds may not be sexually monogamous, for the most part, they are socially monogamous. This means that usually, the same bonded pairs return together to nest again each year and both take care of all the nestlings equally despite some paternal issues. However, there are times when socially bonded pairs break up. Usually, the reason is an unsuccessful nesting event. When this happens, a bluebird might look for a new mate or a new nesting site, or both, to have more success in the future.

Researchers have had a hard time estimating the extent of extra-pair copulation among bluebirds. The best that can be obtained are averages from different field study sites, but there's no complete agreement. For instance, one study found that 5% of males and 15% of female bluebirds were taking care of nestlings that weren't their own, and in 25% of the cases, they observed multiple parenting events. In a later study from the same researcher, multiple parenting events were observed in 35% of the studied cases, and yet another study showed 11% of nestlings were really the offspring of another male. So, these numbers are really all over the place.

There are many reasons why bluebirds would engage outside of their bonded mate. Some of these reasons include the biological need for diversity, low breeding synchrony, having additional males within the population or neighboring territories, or if a nesting spot was on the edge of their territory. Reproductive synchrony is one of the reasons for male bluebird infidelity. The phrase refers to the alignment of fertility between a population of males and females. For instance, one study found that a male might venture elsewhere if the bonded female isn't fertile at that moment. The good news is that extra-pair copulation events seem to occur more in newly paired bonds than in pairs that have returned to each other for another breeding season.

Bluebirds are not the only songbirds that mate socially. Many species of songbirds are classified as socially monogamous, where they share nesting sites and care for nestlings together year after year, but they're not necessarily sexually monogamous. So, when it comes to bluebirds, defining the word mate involves two factors: social partnering and copulation partnering. In most observed cases, the social partner is usually the biological parent of most or all nestlings, but there are occasions where the female has had another copulation partner. In terms of care towards extra-pair nestlings, researchers found that there's no difference in care. Many studies show that there's equal attentiveness despite extra-pair nesting events. Researchers have even taken males away during their females' fertile period in order to lower the male's confidence about parentage, and still, the care was the same.

To some, it might seem a little sad that these special couples are a little unfaithful to each other, but there are biological advantages to this. In the end, the couple still remains socially paired for a long time and provides excellent care to their young.

Bluebirds Nesting and Breeding

As early as the end of February to mid-March, bluebirds begin searching for nest box sites, with those in the south beginning their search earlier than those in the northern regions. Male bluebirds will bring their mates to check out different sites, but it is the female bluebird that ultimately decides where and when to nest. Bluebirds are cavity nesters, which means they use tree cavities or artificial nest boxes. However, cavity nesters in the United States face several dangers, including natural predators and invasive species that may harm or repel them. Native birds that compete with them can also pose a threat.



To protect bluebirds, using specially designed nest boxes and mounting them on metal poles with stovepipe baffles can greatly improve their chances of survival. Regular monitoring and education are critical; unintentional monitoring and protection of nest boxes may inadvertently attract predators.

Nesting may take from a few days to a week, and females may begin laying eggs immediately or may require a period of time known as the "bluebird honeymoon"-a break between nesting and egg-laying that may last up to two weeks. Bluebirds typically lay four to six eggs per clutch, and may lay two to four clutches a year. Eggs are usually blue, but occasionally white, and bluebird eggs are quite small compared to those of robins. The mother usually lays one egg per day and waits until all the eggs have been laid before incubation to ensure that the chicks hatch at a similar time. Incubation lasts from 13 to 20 days, with the duration varying with temperature.

During incubation, the mother may leave the nest briefly to forage or rest but usually stays in the nest box at night. She experiences hormonal changes that cause her to develop a "brood patch" – a featherless area on her breast that helps transfer body heat to the eggs and monitor their temperature. After the eggs hatch, both parents feed the nestlings.

Nestlings grow rapidly and can fledge, or leave the nest, between 16 to 20 days of age. They generally fledge together, though sometimes one may be hesitant. Once they leave, they do not return, except possibly to roost in winter or when preparing to nest on their own. The father then helps the fledglings learn essential survival skills like foraging and exploring their territory. After fledging, it’s a good time to clean and reset the nest box.

Calcium is crucial for female birds during egg-laying. To ensure they get enough, you can supplement their diet with crushed eggshells or calcium powder, as mealworms alone are often low in calcium. Calcium deficiency can lead to fragile eggs and, in severe cases, egg binding – a potentially fatal condition where the egg gets stuck. If a wild bird shows signs of egg binding, seek help from a wildlife rehabber.
In terms of diet, bluebirds primarily eat insects during the nesting season. They feed their young a variety of bugs, which provide protein and moisture. Fledglings have a speckled reddish breast and mostly gray back feathers with some blue tips initially. They are not great flyers at first, and survival rates for fledglings are around 50%. As they grow, they become more colorful and resemble adult bluebirds. Sometimes, juveniles from earlier broods help feed later broods. The nesting season runs from March to September, varying by region, and while some northern bluebirds migrate south for winter, many U.S. areas host bluebirds year-round. As winter ends and days lengthen, the nesting cycle starts anew.

Where Do Eastern Bluebirds Live?

Winter Range: During the winter, they migrate to the southern part of their breeding range, including the southeastern United States. Some may also migrate further south into Mexico.

How Can I Attract Female Eastern Bluebirds to My Garden?

Where Do Bluebirds Like to Stay?

What Do Bluebirds Like to Eat?