Fresh (liquid) water is a must. I've included a picture from winter when a whole flock visited my birdbath ... and it is right on my deck! The trick is to have a birdbath with a built-in heater or an attached heater to keep the water fluid during the chilly months of winter. Families will visit the birdbath throughout the summer, too, especially in times of drought.
#2 Food! Bluebirds aren't fans of what I put in my seed feeders. They are fans of worms and insects, and dried mealworms are a quick and relatively cheap invitation to birds to come by my yard. However, lots of birds like mealworms. Messy birds, like Starlings, too. So I built a bird feeder for small birds to offer up the mealworms. It looks like a house, with a peaked roof and two tiny holes on either side. Little birds like bluebirds, chickadees, and finches can fly in and fly out. The sides are glass, so watching them in action is a treat. (I do put some mealworms in the different feeder for the bigger birds to keep them happy ... and to keep them from trying to break into the mealworm house.)
#3 The Nesting Box. Bluebirds are pretty particular when it comes to raising babies. They are definitely not fans of building a nest close to a structure, so it is best to put the nesting box as far away from the house as possible. Luckily for me, we have the corner lot, which means the nesting boxes are way back -- over 35 yards from the house (and other houses, as we back up to a street). I have multiple boxes so that other birds such as wrens can make a nest without competing with the bluebirds.
I favor nesting boxes with a slotted opening. Peterson boxes and other styles with a hole for entry work great in rural areas, fields, and trails. From my experience living in suburbia, the slotted boxes are a better choice. I have had successful clutches year after year with the slotted boxes. One major challenge bluebirds face in neighborhoods is the European House Sparrow (which is an invasive species ... don't get me started ). The slotted opening gives the bluebirds a chance to flee the box so they can counter-attack to chase away the house sparrows.
And, we're "blessed" by a lot of cats ..... but no Black Rat snakes. You will notice my nesting box has chicken wire around the slot (and on top of the house, and on the fence post, and along the fence line) to deter cats and squirrels from invading the bird's nest. (Squirrels will try to chew the opening bigger and make the nesting box their home. Chicken wire fixes that! It's painful on the teeth.) However, if you are in an area with egg-loving snakes, a predator baffle is 'the way' to go (see the link to an article on the University of Missouri Extension (MU Extension) site below).
From clutch to brood: I am a proud bluebird papa. The most recent was a clutch of four, which became a successful brood of 4. Last week, the entire family left. I am an empty nester again.
It is good to check on the nesting box weekly once it is in active use. Doing so will also inform you when the eggs are hatched. Before the eggs hatch, the bluebird pair will fly up to a high branch or overhead power line and watch as you near the box. They'll chatter a little, too.
You'll know when the eggs hatch. The chatter is more intense, and ..... this is the cool part .... they will begin swooping your head while making a clicking sound. They will swoop squirrels, they will swoop cats and other birds. If they are brave enough to swoop a human, you know they are fit parents.
Checking on your birds weekly is especially important. Typically, I just approach the box and not open it. The bluebirds' activity lets me know what stage the clutch/brood is at. If you don't notice the protective behavior, then something is wrong. One year, I only noticed one parent (the male) entering and leaving the box. The female was absent. As bluebirds frequent other yards to look for food, I assumed the worst. By checking on the box weekly, and opening it in this odd instance, I found three dehydrated bluebird hatchlings. I took them immediately to a nearby Nature Center/Bird Sanctuary, where they were rehydrated, raised and released.
While my most recent fledglings have left, there is still time for the bluebird couple to come back to my yard to raise 1 (or 2) more broods before summer ends. Here's hoping!
Here are a few resources with lots of great information about bluebirds, their habitats, and how to attract them. Happy birding!
MU Extension resource page on attracting (and keeping) bluebirds on your property
https://extension2.missouri.edu/g9429
Missouri Bluebird Society
https://missouribluebird.wordpress.com/
Missouri Dept. of Conservation information about Eastern Bluebirds
https://nature.mdc.mo.gov/discover-nature/…/eastern-bluebird
Cornell Lab of Ornithology The Cornell Lab
https://www.allaboutbirds.org/guide/Eastern_Bluebird/id
