Bluebird Babies: All About the Nesting Season

Bluebirds start scouting for nest box locations as early as late February and into mid-March. These times can also depend on geography, with bluebirds in southern states tending to scout a little earlier than those in northern states. The male bluebird will take his mate to different locations for inspection. Ultimately though, it's the female who decides when and where she'll start building her nest. Bluebirds are cavity nesting birds, meaning they nest in tree holes and artificial nest boxes. Unfortunately, in the U.S., cavity nesting birds face a lot of threats. Threats not only come from predators, but also invasive birds that evict them, often fatally harming them in doing so. Threats can also come from competing native birds. To protect our bluebirds, getting a nest box specific for bluebirds and mounting it to a metal pole with a stovepipe baffle can make a world of difference. Aside from that, regular monitoring and education can really help save their lives. Never put up a nest box if you don't intend to actively monitor and protect them. Otherwise, you're likely putting up a lunch box for predators that a bird can't escape from. Nest building can take a few days up to a week, and she may lay her eggs right away or take what's known as a bluebird honeymoon. Many other birds honeymoon also. This is just a period between nest completion and egg laying, and the gap could last as long as two weeks. Bluebirds lay a clutch of four to six eggs on average, and she may have between two to four broods, or sets of babies, in a single year during the nesting season. Bluebird eggs are usually blue, but occasionally bluebirds will lay white eggs. Eggs are very small, about three quarters of an inch. Robin eggs, for comparison, are also blue, but noticeably larger. They're about one inch to one and a quarter inch. Usually, a mother bluebird will lay one egg a day, but she won't actually sit on them until the last egg is laid. By waiting to incubate until all of her eggs are laid, she ensures that the babies will hatch close to or all on the same day. The incubation period can be anywhere between 13 to 20 days long. During colder spells, the incubation period may be longer, and on warmer spells, the incubation period could be shorter. While incubating her eggs, the mother will occasionally leave the nest to forage or take a break. She can be gone for as little as 15 minutes, up to an hour, and she may leave her nest once per hour. However, she'll usually remain in the nest box all night. The mother bluebird will experience a change in her hormones during the nesting season, and this prompts her to lose a patch of feathers on her breast. This is called a brood patch. In her nest, she'll shimmy over her eggs, and this is to make sure she's distributing her brood patch over all of her eggs. The brood patch allows her not only to transfer body heat to her eggs, but also to detect egg temperature. With her brood patch, she can tell if her eggs are too cold, too warm, knee-turning, or are just right, and she'll alter her attentiveness as needed. Once the eggs hatch, both mother and father will bring food to the nestlings. Bluebird nestlings grow fast and can fledge the nest anywhere between 16 to 20 days old. Usually, they'll fledge within hours of each other, but on occasion, a nestling might be reluctant to leave. Once they leave the nest, that's it for them. They won't return again, except maybe during winter to roost, or when it comes time for them to nest on their own. For a week or two, the father shows them how to be real birds. He'll take them to feeders, show them how to hunt for bugs, find water, and show them the territory. If you're managing a nest, once they fledge, this is a good time to remove the old nest, give the nest box a good cleaning, and reset it. You may even want to rub unscented soap around the top insides and interior roof of the nest box to prevent wasps from taking over. After you reset the nest box, if it's still nesting season, the mother bluebird will usually return to start building a new nest for the next brood. It could be within a day of the baby's fledging or even up to two weeks after. Something many of us don't realize is how much calcium female birds use up in order to lay their eggs. Fortunately, calcium is a pretty ubiquitous mineral. However, mealworms are known for being calcium deficient. If you're feeding mealworms to your bluebirds, you may want to supplement their calcium. All it takes to do so is saving your eggshells, heating them to 200 degrees Fahrenheit for 30 minutes, and crushing them up. Then you can mix the eggshell flakes in with mealworms or just put it outside for the birds. There's also calcium powder available that you can use to coat mealworms with. When a mother bird is deficient in calcium, she may lay more fragile eggs that are prone to breaking. If she's really deficient, some studies have reported mother birds eating their eggs. But another issue is when a mother bird is egg bound. This is when her egg gets stuck and it can be fatal. If you suspect a wild bird is having any kind of trouble with egg bound, search for a because they may be able to help. When it comes to diet, bluebirds will stick mostly to bugs more than seed during the nesting season. Not only will they eat the mealworms you provide, but a location rich with plant life and trees will be rich in nutritious bugs and grub. You'll see bluebirds feeding larvae, moths, bumblebees, June bugs, and so many other bugs to their babies. In fact, not only are bugs filled with protein and nutrition for nestlings, they're also the source of water. During the nesting season, many songbirds will be strictly feeding their young bugs and grub. You can recognize fledglings by their speckled reddish breast. Their back feathers will mostly be gray with just the ends of their flight feathers and tail showing up blue. In the beginning, they're not the best flyers and many sources say only about half of baby bluebirds survive once they leave the nest. As the season progresses, juveniles will become more vibrant in color looking more and more like bluebirds. Juveniles also sometimes help out. It's been reported that juveniles of an earlier brood will sometimes help feed nestlings of a later brood. The whole nesting period lasts from about March to September, with the months and dates varying based on region. Come winter, some of the bluebird populations of the north will migrate south for food and resources, but in general many regions of the U.S. host bluebirds year-round. As winter melts away and the days start to get longer, the whole cycle of nesting begins again.