After the arctic freeze we experienced a short time ago, you may not believe Spring will be upon us soon, but it will. Tennyson reminds us what a young man’s fancy turns to when Spring comes, and the same applies to other animals. Male Eastern bluebirds will soon be singing forcefully, defending their territory and attracting a mate. The male seeks out nesting cavities and tries to entice the female to inspect the cavity and convince her that it is a good and safe place to nest and raise their young. Nest construction soon follows, and the laying of eggs signals the start of the next generation.
If you are like many other people, you may have one or more Eastern bluebird nest boxes installed in your yard or on your farm. Bluebirds use natural cavities (such as those made by woodpeckers), but in some places, snags, another name for standing dead trees, may not be present. Artificial nest boxes have played a huge role in the recovery of bluebirds from very low population numbers in the middle of the 1900s. Bluebird boxes are readily found in hardware, feed and seed, and other birding supply stores. There are also many online options for purchasing bird houses, and of course, you can always build your own. Whatever option you choose, just make sure that you are building or buying a structure that is properly designed for Eastern bluebirds or any other cavity-nesting species you might want to attract. Cornell Bird Laboratory has a website with information on just about any topic related to bird nesting structures, including nest structure designs, proper placement and spacing, and maintenance. The website also has tips for dealing with invasive, non-native birds, such as the house sparrow, European starling, and much more.
Nest boxes are most productive when they are monitored and kept clean and in good structural condition. The following are some of the things to look for when preparing your nest box for Spring:
- Inspect and repair holes and cracks that would allow precipitation and wind in. Small holes can be filled with wood putty. Larger ones may require replacing that structural element. Cracks can be glued and clamped or filled with wood putty.
- If the entrance hole has been enlarged by squirrels or woodpeckers, install a restrictor that returns the hole to the proper diameter for the species you are trying to attract. Enlarged holes make it easier for invasive species like European starlings to nest in. Restrictors are available commercially, or you can construct your own from sheet metal.
- Evaluate the location of the nest box. Have branches from surrounding trees grown enough last year to provide a bridge for rat snakes to use and invade your nest box? If so, prune the branch or move the nest box to a safer location. Also, make sure your predator guard is intact and still in its proper location.
- Use the information you gathered from last year’s monitoring to decide whether other actions are needed. Were there multiple male Eastern bluebirds fighting over the one nest box you have in your yard? You may need to install another one (or more). Just make sure you space them at least 100 yards apart. Bluebirds are extremely territorial during the breeding season.
- Also, based on your monitoring observations, were there failed nesting attempts? If so, were you able to determine the cause? Did house sparrows move in before bluebirds, or worse yet, were the bluebirds able to construct a nest and lay eggs, only to have house sparrows destroy the eggs or kill the hatchlings or nestlings? They will even attack and kill adult bluebirds. If bluebirds are not able to nest year after year, then those boxes should be taken down until local populations of house sparrows decrease or are eliminated. Unfortunately, there will be cases where populations of the invasive birds cannot be sufficiently reduced, and nest boxes should not be installed at all rather than become death traps for Eastern bluebirds or other native birds, as well as house sparrow nest sites.
- European starlings and house sparrows are non-native, invasive species. As such, they may be dealt with using lethal, legal, and humane methods. That topic won’t be elaborated on in this article. However, one other thing that should be pointed out is that brown-headed cowbirds, though a nest parasite of Eastern bluebirds and other species, are a native species and as such are federally protected. Their eggs and chicks should not be harmed.
- Both Sialis, and the South Carolina Bluebird Society, strongly recommend removing nesting material between clutches and at the end of the nesting season. One reason given for removing nesting material is to reduce the number of ectoparasites, mainly mites and blowfly larvae. A second reason is that while bluebirds may return to the same nest box in which a first clutch was successfully raised, they do not lay the second clutch in the same nesting material. Instead, they build a new nest on top of the old one. In fact, they will build a new nest in the same nest box before each subsequent clutch is laid. This results in each clutch of eggs and hatched young getting progressively closer to the entrance hole, making it easier for predators to reach them. For these reasons, remove old nesting material after each clutch has fledged. However, this requires you to monitor your nest box regularly. Eastern bluebirds fledge anywhere from 16-21 days after the last egg of the clutch is laid. The female starts the new nest about 5 days after the young have fledged. Do not open boxes to monitor between days 13 and 21 as this may cause the nestlings to fledge prematurely.
- When cleaning nest boxes, wear a mask and gloves and sanitize your hands immediately afterward. Old nests should be placed in a sealable plastic bag and put in the trash or disposed of outdoors far away from nest boxes. Use a wire brush to remove any debris that is stuck to the sides or bottom of the box. If additional cleaning is required, scrub with a soapy solution and rinse, or spray with a 10% bleach solution and allow to dry for 24 hours.
For additional information on establishing and monitoring Eastern bluebird nest boxes, see Clemson University Home and Garden Information Center Fact Sheet 2908, Providing for Bluebirds: Guidance for Bluebird Nest Box Establishment in South Carolina.
Author(s)
TJ Savereno, Cooperative Extension, Forestry and Wildlife Agent
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