If the birds held a popularity contest, Bluebirds would probably win. Everyone loves them. Perhaps that’s because they’re so well mannered. They help us by eating the bugs that bug us. They take good care of their families, with the males defending their territories while the females fuss over the nestlings. And when the sun hits their feathers, just so, they shine with the most amazing sky blue.
It’s a good thing many people like bluebirds, because they could use our help. All three bluebird species have declined in numbers since the early 1800s. There are several reasons.
Many winters during the 1890s were exceptionally severe, and many birds died. It takes time for populations to recover, and the repeated cold weather was very damaging, at least to Eastern Bluebird numbers (no one was counting Western and Mountain Bluebirds at that time).
During the last several hundred years, much land that used to be forested has been cleared for farming. At first this helped the bluebirds by providing open areas for feeding. But eventually so much land was cleared that there were no trees available for perching and nesting. Also, because dead trees are now usually cut down by people, fewer rotting trees with holes in them are available for the birds to use. If the birds can’t find a suitable cavity for their nest, they are unable to breed for that season.
Urban and suburban landscaping is not very suitable for bluebirds. While there are trees and open spaces, manicured lawns and bug-free gardens provide little in the way of food. Again, trees with cavities are typically removed, so there is no place to nest.
In the 19th century, House Sparrows (1851) and European Starlings (1890) were introduced from Europe. Both these birds also build their nests in cavities. They compete with the bluebirds. Since they are bigger and stronger, they are able to kill the nesting bluebirds and their young, and use the site for their own nest. Native bird species, such as wrens, swallows, and chickadees also compete for housing with bluebirds. However, these birds are beneficial, and their nesting is to be encouraged. It sometimes helps to provide these birds with their own custom-designed nest boxes so there is housing for everyone. Where their ranges overlap, the three bluebird species will not share territories, so they compete with each other as well.
Diminished food resources also limit population size. Starlings eat berries in the winter, and large flocks will quickly pick a bush clean. This leaves fewer berries for the bluebirds. Gardeners who spray toxic chemicals on their gardens kill the bugs that bluebirds eat. And, they may accidentally end up poisoning the birds that come to eat the sprayed insects.
People have helped create some of the problems that bluebirds face, but they can also help provide solutions. In the 1920s, a nationwide campaign was started to build bluebird nest boxes and put them on metal poles, fence posts, and trees in suitable habitats. These man-made boxes replace the hard-to-find natural cavities in old trees. While they are not quite as comfortable as a hole in a tree (a solid tree provides better insulation), these boxes have been readily accepted by the birds.
Compared to natural cavities, man-made boxes can provide better protection against predators. There are a number of ways to thwart House Sparrows. The North American Bluebird Society has a very helpful article on this topic. House Sparrows should never be left to fledge young in a bluebird nest box, as this increases their population and further harms the bluebirds. Nest boxes should have a side or top panel that opens, so you can check them weekly. Carefully opening the box will not greatly disturb the family nesting inside.
Starlings, being bigger than bluebirds, need bigger entrance holes. By making the hole into the nest box just the right size, bluebirds can get in but these intruders cannot.
To make a deeper tunnel, drill through an extra 2-inch thick block of wood placed over the entrance hole. Predators, such as raccoons, house cats, deer mice, and chipmunks, will not be able to reach far enough inside to hurt the young. These predators have a harder time climbing a smooth metal post than the rough bark of a tree. In addition, there are various guards that you can put on the pole to keep these animals from climbing it. Many of these predators will gnaw on the wood around the entrance hole to make a larger opening. Then they can get inside. You can buy or make metal guards that predators cannot chew through. It is important to build boxes that are safe for the birds who will nest there.
All these conservation efforts have been very successful in the east. Populations of Eastern Bluebirds are growing rapidly. Mountain Bluebirds are also responding to the increase in nesting sites. Unfortunately, Western Bluebirds aren’t doing as well. Their population is still declining, especially in California.
If you would like to provide a nesting box for the bluebirds in your yard, the first step is to identify which species of bluebird you have. Then build or purchase a box that is right for that species. The North American Bluebird Society website is a great source of reliable information. Commit to being a trustworthy and responsible landlord, and you’ll experience the joy of watching a pair of bluebirds raise their family. They provide us with so much happiness… isn’t it time we returned the favor?