The world is divided into two groups of people: Those who have recently seen a bluebird, and those who will see one soon. Eastern bluebirds are making a comeback.
Bird populations are crashing worldwide due to climate change, habitat loss and other manmade causes. The number of eastern bluebirds in Maine, however, is increasing. The best evidence comes from the Christmas bird counts that take place throughout the state each year. These historical records go back a century.
Thirty years ago, only about a dozen bluebirds were spotted in the entire state during the holiday season. Numbers began to increase about 20 years ago, and now exceed 600. Most are wintering in the southern part of the state, but even in eastern Maine, a few tough it out.
The same trend shows up on eBird, the widely used online database managed by the Cornell Lab of Ornithology. Ten years ago, only one bluebird was reported north of Augusta in January. This year, dozens of reports stretched northward to Bangor, while the numbers in southern Maine multiplied.
Before congratulating ourselves for restoring the iconic bluebird of happiness, it’s helpful to understand why it disappeared in the first place. At one time, it was a common bird around the farms and fields that expanded across the state from the late 1800s through the middle of the last century.
Small family-owned farms, with lots of woodland edge habitat, were ideal for cavity-nesting bluebirds. As many small farms consolidated into fewer large farms, nesting sites diminished.
Metal fence posts replaced wooden posts, taking those knothole nesting sites off the map. Excessive pruning of trees, especially in apple orchards, removed more of the knotholes that bluebirds relied on. Encroaching suburbs nearly finished the job of kicking bluebirds out of the state.
So did avian competition, after house sparrows and European starlings were brought from England and released in America. These two cavity-nesting species proved to be more aggressive, wresting the few remaining nest holes away from their native owners.
However, a recent decline in these two invaders may have helped the bluebirds rebound. Starling numbers have diminished by half since 1966, and house sparrows have decreased even more rapidly over the same period.
Bird houses apparently make a big difference. Bluebird boxes have become popular, and organized volunteers have erected hundreds. The Downeast Chapter of Maine Audubon has established a bluebird trail, and the results are impressive.
According to the chapter’s website, 2020 was a noteworthy year. A review of 346 houses across Hancock County showed that 387 eastern bluebirds, 654 tree swallows and 195 black-capped chickadees successfully fledged during that breeding season.
It takes keen attention to monitor bluebird nesting success. When the season begins, males woo females by bringing them nesting materials, and perhaps offering them a choice of cavities. She makes the final decision and builds the nest. She may even begin nests in all the offered choices, making it tricky to count used nests. Plus, bluebirds often raise two broods per season.
The fact that more tree swallows than bluebirds raised families in bluebird boxes is normal. Bluebirds defend their nests from encroachment by other bluebirds and will confront pairs trying to nest within a hundred yards. But bluebirds don’t object to neighboring tree swallows or house wrens, which happily take over unoccupied boxes within the contested zone, even boxes mounted on the same pole.
We’ve also gotten smarter about bluebird box construction. For instance, a 1 1/2-inch hole admits bluebirds, but excludes starlings. Bluebirds don’t care if a birdhouse has a perch. House sparrows do. House wrens don’t need a clean box. They will remove any old nesting material before building a new one. But bluebirds just build a new nest on top of the old one, leaving themselves susceptible to parasites left behind by the previous occupants.
It may be too late to clean your bluebird boxes this season. Many bluebirds are already back and investigating potential sites. However, if you don’t see any around yet, a little last minute birdhouse maintenance may help to keep them disease-free.
The long-term future of bluebirds remains questionable. Fortunately, they are hardy enough to winter here, foraging on fruits and berries. Unfortunately, manicured lawns and exotic ornamental plantings do not provide the natural winter food they need.
Fortunately, there is a slow trend toward more native plantings around malls and subdivisions. Unfortunately, overuse of pesticides is eliminating insects and caterpillars, their summer diet. Sometimes bluebirds just can’t catch a break.