A female bluebird sits tight on her nest. Photo: Bob Orthwein


A female bluebird sits tight on her nest. Photo: Bob Orthwein On a sunny 11 August 2010, I opened the front panel of Nestbox-108 in Delaware State Park to find a flattened grass nest holding several dozen black cherry seeds. The wild fruit had supplied “bluebird Gatorade®” for four nestlings that had weathered the warmest days of summer as the last bluebird family of the season. They had been due to fledge on August 8 after spending 18 days as nestlings. The success of this last nest ran the park’s tally up to 113 bluebirds, and raised the season’s grand total to 237 blue thrushes raised at seven nestbox trails in Delaware County, Ohio. Bluebirds laid 317 eggs, 244 (77%) hatched, and 237 (74.8%) fledged. Most impressive, once hatched, 97.1% fledged. The 2010 bluebird nesting season lasted 129 days from the county’s first blue egg on April 2, to its last nestling fledged on August 8. After 43 years of recording data, 28 March 1981 stands for the earliest first-egg date and 11 September 1988 is the latest date when a fledgling flew from its nest.

A sliding panel, tightened with screws, is used to close the back ventilation slot, whereas felt weather stripping plugs the front slot to make it cozier for roosting bluebirds during winter months.After I cleaned out the used bluebird nest and screwed the front shut, I prepared the box for winter. I closed or plugged both of the quarter-inch wide ventilation slots that allow cross-ventilation during the hottest days of summer. A six by 1-1/4-inch slotted panel made of Masonite® or recycled plastic, slides under two screws to cover the quarter-inch vent slot above the box’s back panel. To close the vent above the front panel, I stuff it shut with a six-inch strip of felt weather stripping. Usually, the quarter-inch drain holes in the floor are already plugged with hibernating spiders or other arthropods, so I no longer plug drain holes with dowel rods. The practice of winterizing nestboxes to convert them into roost-boxes is a standard practice among bluebird conservationists. Bluebirds that stay for the winter, or migrate through the area, will roost communally during harsh weather. In the past, I have used a machinist mirror and penlight to count as many as seven bluebirds huddled together to share body heat through a cold, wintery night. Other observers have counted more than a dozen bluebirds entering one box while seeking shelter.

In 1986, I used the coin-toss method to determine which boxes in Delaware State Park would be winterized, and which ones would be left “open” in a controlled scientific study that revealed that as the winter progressed, wintering bluebirds learned to roost in winterized boxes rather than ones that remained ventilated. To show this, at the end of each month from November through March, I collected and weighed fecal deposits and seed packets regurgitated from bluebird gizzards. I found that bluebirds roost in a few boxes in December, but most roosting occurs in January and February. While winterizing nestboxes increases the chances that roosting birds will survive, food availability is also a huge factor that determines survivability, and “spring cleaning” reveals how well bluebirds endured the trials of winter.

In early March, I start to prepare my trails for the upcoming nesting season, and I want everything ready by March 15. For example, I return 102 nestboxes and their predator (raccoon) baffles to two Tree Swallow nestbox grids on the Delaware Wildlife Area. I also add fresh chassis grease to poles in Delaware State Park and other locations, and I reopen ventilation slots above the front panels. I reopen the back vent in late May. I start to gauge the severity of the previous winter when I clean debris from nest chambers during spring cleaning. By 11 March 2010, I had salvaged 20 winter-killed bluebirds for the Ohio Wesleyan Zoology Museum. One bird wore a leg band that my class of seven middle school students from the OWjL Academic Camp had attached on 10 June 2008. On 3 March 2010, I found the lone, dead male in a nestbox 230 yards from where it grew up with four siblings. I can tell future classes about this find along with the assumption that the bird had fathered families of its own during the 2009 season.

2010 was a good year for these four-day-old bluebird nestlings to grow and fledge. Even after finding 16 winter-killed bluebirds in DSP, one at the Alum Creek State Park office trail, and three in one box on the campus of the Methodist Theological School in Ohio, I felt relieved since I expected to find more dead bluebirds after a winter with several freezing rain events that encapsulated rose hips, poison ivy berries, moonseed, wild grapes and other dried morsels that provide survival food for wintering birds. Bluebirds cannot chip thick ice from food items, but if a bright sun melts the ice coverings by afternoon, then the birds have a chance to survive.

The winter’s death toll was expressed in my annual mid-May nest count. I counted 36 active nests in my data book that represented 7.7% fewer nests than 39 nests counted in 2009 at the same locations. The 2010 season progressed as bluebirds attempted 73 nests with eggs and 60 (82.2%) families successfully produced an average of 3.95 fledglings per nest. Of 13 failures, House Wrens left no doubt at five nests where they dropped punctured eggs in front of boxes before adding sticks to cover the usurped bluebird nests. Three nests failed for unknown reasons but hawk predation is always a possibility since Cooper and Sharp-shined hawks are common. Sometimes, if a monitor takes time to “think like a hawk,” they will move a nestbox away from a tree or other structure that hides a hawk’s sneaky approach to pluck an unsuspecting bluebird from its perch. Tree Swallows, House Sparrows, an herbicide application, a mower collision with a nestbox’s pipe mount, and competition from another bluebird account for one bluebird nest failure each.

In 2000, I decided to identify the three egg-laying periods within the bluebird nesting season in Central Ohio. I examined all records going back to 1968 and found 31 nestboxes that had housed three successful bluebird nests during the same season. The data showed first-eggs from first nests appeared before May 15. Eggs laid between May 16 and July 5 represented the second nesting period, and first eggs deposited on July 6 and later made up the third egg laying period. Using these values, I examined sixty successful nests in 2010 and found that 34 (56.7%) were started during the first period, 24 (40%) in the second, and only two (3.3%) started after July 6. In habitats where vegetation is mowed by machines or grazing animals throughout the nesting season, the first and second nestings for bluebirds are fairly equal, whereas the third nesting period can represent zero to 15-percent of a season’s nests, depending on availability of insects as determined by weather and other factors. Summer droughts usually result in poor nesting conditions and the third nesting period might be absent. On the other hand, any combination of weather conditions that supports healthy insect populations will support a prolific nesting season for bluebirds.

When I look at 29 successful nests in DSP in 2010, I find that 16 nests were successful in the earliest nesting period, 12 in the second, and only one nest produced a first egg after July 6. There are mowed lawns in the park, but many bluebirds nest where boxes stand in grasslands that are brush-hogged only once in the late fall after the nesting season. I am very thankful that the park supports the effort to promote nesting bluebirds by trimming large areas around my boxes to keep the habitat from succeeding back into a forest. Once spring arrives, the grasslands start to grow taller to produce a profusion of colorful wildflowers that support healthy populations of butterflies and moths that have won many fans that stalk both flowers and butterflies with binoculars and field guides in hand. The patches of grasslands also attract “after supper” campers and park visitors wishing to see grazing deer that appear at dusk.

Paired bluebird boxes stand in a great habitat for bluebirds and Tree Swallows beyond a “target basket” used in disc golf in Delaware State Park.Some bluebird enthusiasts would like to see the grasslands maintained at shorter levels so nesting bluebirds can find it easier to pluck insects from the ground throughout the entire season. Nonetheless, I agree with the present policy that there should be room for a greater variety of species. Wherever there is a bluebird habitat, I have placed a nestbox for them. Also, to lessen competition from Tree Swallows, I have placed a second box within five yards of the first, so paired boxes are found throughout the park. The park’s Tree Swallow tally for 2010 is 417 raised, a considerable portion of 1,002 fledged from all of my trails in 2010.

For several years, a new bluebird-friendly activity, disc golf, has been active in the park. The new 20-basket course is free to the public and covers a large area near the park’s marina, then surrounds the ice-skating pond and proceeds to cut through two woodlands leading to include two picnic areas. The Frisbee sport is very popular and requires that the course be mowed, making perfect bluebird habitats in the process. Also, a second disc golf course is being developed in the north end of the park to serve visitors and the camping public that rent the park’s popular campsites that number 212. I guarantee that bluebirds will also enjoy their new mowed habitats, and I’ll make sure they have proper nesting sites for their families. Happy Bluebirding!