Observations in Nest Engineering

Article and photos by FMN Stephen Tzikas

Feature photo:  Eastern Bluebird nest, Box 3. May 1, 2021, Langley Fork Park.

Animals can have fairly skilled abilities, like that of a beaver building a dam, wasps constructing a hive, an octopus maintaining a garden to hide and reinforce its den entrance, or a bird building a nest. Birds can build nests in a variety of areas, urban or rural.

In 2021, I volunteered to become a bluebird monitor at the Langley Fork Park, in McLean, VA. It is one of the great variety of master naturalist programs available to volunteers. I was partial to it primarily because I had a pet parakeet as a child and knew how extremely intelligent and friendly these birds are. In 2022, I became the trail leader.

The Virginia Bluebird Society’s monitoring program offers a great opportunity to see new born birds very close. It’s not just the birds I find interesting, but also their nests. My favorite Bluebird monitoring document is found at this link from the North American Bluebird Society:

It is a useful document that discusses the identification of birds, eggs, and nests.

House Wren nest, Box 9, July 16, 2021, Langley Fork Park.

It’s all fascinating and perhaps the most interesting to me, as an engineer, is how nests are made. Each species has a unique nest. One might ask why and how? I haven’t found too much literature on why each type of bird builds a nest the way they do. So I will speculate a bit.   At Langley Fork Park the Tree Swallows and Eastern Bluebirds are the most successful birds inhabiting the boxes, with the Tree Swallows having a slight edge. In 2021, we had one successful House Wren nesting event. While maintaining the bird boxes this Fall, I noticed a mouse built a nest in a birdbox surrounded by overground shrubs, which allowed it to reach the entrance.

Eastern Bluebirds build neat, cup shaped, woven nests of fine grass or pine needles. Tree Swallows

Tree Swallow nest, Box 5, May 21, 2022, Langley Fork Park.

build nests of coarser grass lined with feathers. Their cup is flatter than those of Eastern Bluebirds. House Wrens build haphazard nests of twigs, occasionally lined with feathers. House Wrens pile twigs creating a cavity in which they choose to nest, acting as a barrier between nest and entrance. House Wrens can be fierce competitors for nest sites, but generally speaking, the House Wren, as a species not as competitive as the Eastern Bluebird or Tree Swallow, has a security structure embedded as part of its nest.

Birds can also build unlined eggless “dummy nests” in nearby boxes to reduce competition. Dummy nests are also built by males, perhaps to offer the females some choices on her preferred location and once chosen, can be finalized.

From the Factsheet link I provided, the mouse has a messy nest. Mice usually make their nest from a variety of materials, such as grass, leaves, hair, feathers, shredded bark, moss, cotton, or shredded cloth. My son had a gerbil as a pet. I can say gerbils are not as intelligent as birds. Given this observation of their fellow rodent, and that mice are quite timid and scared, their nests are conducive to hiding. A mouse did not make a quiver when I opened a bluebird box weeks after the end of a season and found a mouse nest. Its nest was built to hide at all costs. Upon emptying the nest the mouse quickly ran away.

House Wren nest, Box 9, side view from 2021 season.

Eastern Bluebirds and Tree Swallows, who are competitive and successful, perhaps have the luxury to build a more comfortable nest given their abilities to defend their turf. The Eastern Bluebird, perhaps being particularly skilled, can find those extra soft grass blades and soft twigs, being quite comfortable for a refined nest for their hatchlings. The Tree Swallow, who includes some coarser twigs, can make up in their selection of cushy feathers to keep their young nestlings comfortable.

If birds were people, we might amusingly attribute the following characters to their work:

  • Eastern Bluebirds – build with “engineering precision”
  • Tree Swallows – build with warmth and comfort
  • House Wrens – build with safety and security


Bluebirds at Langley Fork Park Continue to Thrive

Feature photo: Bluebird nestling residents of Box 6 (May 21, 2022). What are they thinking?

Article and photo by FMN Stephen Tzikas

The 2022 Bluebird box monitoring season at Langley Fork Park in McLean was my second year, and first as its trail leader. The trail leader duties came unexpectedly, but it successfully concluded thanks to the existing and new trail monitors who helped me with this success. Although I wrote an article last year on the extraordinarily successful season at Langley Fork Park, in part due to the cicada bounty, I was pleasantly surprised that this year’s Bluebird fledglings approached very close to the number we had last year.

In 2021 we nurtured 63 total protected birds which included 26 Bluebirds. In 2022 we had 57 total protected birds which included 24 Bluebirds. This can be contrasted to the 5 years prior to that in which Langley Fork Park monitoring succeeded with about 40 protected birds per year which included about 5 Bluebirds a year. Since our efforts are on behalf of the Virginia Bluebird Society and the Bluebirds themselves, having about a 5-fold increase in Bluebirds these past couple years was phenomenal.

As trail leader, I had a closer look at the total 7-year record of data at Langley Fork Park in order to determine if any changes in the location of the Bluebird boxes were necessary to increase the effectiveness of the Bluebird program even further at Langley Fork Park. This data is part of the Nest-Watch database administered by Cornell University. I found the record-keeping in the years prior to 2021 to have some gaps, but this did not detract from the large increases recorded for the Bluebirds at the park. Nonetheless, the gaps were an interesting comparison that should not be ignored for a program’s quality control. Monitoring in prior years were not always on a weekly cadence, and it was not certain if preventive maintenance was rigorous. While I could infer final fledgling counts on what was recorded, these numbers could have been a bit higher and a good maintenance regimen could have made a nest box habitat resilient for an immediate welcoming of a new set of Bluebird parents during critical times for egg laying. This is contrasted to a strict weekly check on the birds in 2021 and 2022, and immediate attention to issues of concerns: wasp nests, ants, predators. For Bluebird monitors, I can’t emphasis enough how important these matters are. Bluebird monitoring trails should have an adequate number of team monitors to keep pace and avoid burdens with scheduling for a trail that has too few monitors.

With this analysis I did have enough data to make some conclusions for future planning. In the past 2 years, 3 of the park’s 10 boxes had successful Bluebird nestlings, while in the entire past 7 years, 6 of the 10 boxes were home to successful Bluebird nesting attempts. Considering that Tree Swallows are also a protected bird and the main successful competitor of the Bluebird boxes, our Bluebird attempts are good.   But can we do better? These are decisions for our trail that may help others in their trail decision-making too.

Before the close of the 2022 season, our team suggested that moving boxes 1, 4, 7, 9 might help the Bluebirds, because currently they had some issues with predators and intense competition.

The data showed that boxes 1, 2, 5, and 9 never had Bluebirds.   We also have the opportunity to add an 11th Bluebird box which will be determined at a later date. While boxes 2 and 5 may never have had Bluebirds, they are in good locations and have other active protected birds nesting here. These will not be relocated for now.

  • Box 1 is in a fairly hidden area. By moving it closer to the parking lot it may get more attention by the Bluebirds.  There is some playground equipment here, but on closer inspection it is for adults to exercise who are not likely to interfere with the box.  The location is more bushy, so it may also attract more House Wrens too.
  • Box 4 has had occasions of broken eggs from intense competition.  Moving it from the corner of the field to a more bushy area closer to some benches could improve it.
  • Box 7 may be too close to a tree with snake predators. Moving to a more bushy area a few feet away may help.
  • Box 9 is in a fairly active area with baseball activity, and relocating it closer to Box 8 may help. The advantage of the new location is that it is slightly less active and has more trees, but it is not necessarily a suggested 100 foot separation from Box 8.

The 2023 season will evaluate these adjustments.

Be a Citizen Scientist at Wolf Trap National Park for the Performing Arts! Bluebird and Purple Martin monitors needed. Training March 15th

Orientation and Training
Wolf Trap National Park for the Performing Arts
1551 Trap Road, Vienna, VA 22182
Sunday, 15 March 2020
1:00 to 3:30 pm

The National Park Service and Friends of Wolf Trap, would like to enlist the help of a team of volunteers who would form a Bird House Monitoring Team to monitor and maintain the Bluebird boxes and Purple Martin housing at the Park. No experience is necessary, as volunteers would be provided with training and guidance by our lead bluebird trail volunteer, Mr. Dale Thornton. Volunteers would learn about Bluebird stewardship efforts, including how to monitor the nest boxes, nest identification, and collecting and reporting nesting data to track population trends. In addition, volunteers would receive training from Mr. Mike Bishop of the Northern Virginia Purple Martin Initiative who will provide an overview of the Purple Martin and the process for monitoring and maintaining the colony.

The bluebird and purple martin monitoring season typically starts in late March and continues through August.  Nests are monitored on a weekly basis during the spring/summer nesting season and volunteers will help with box repair and maintenance during the off season, on an as-needed basis.  A team of trained monitors who will work on a rotating basis throughout the season and continue next year and into future seasons.  Ideally, each trained volunteer would be on a three- or four-week rotation; however, the monitoring schedule and associated details will partly depend upon how many people choose to volunteer.

The interested volunteers should be adults who have received the appropriate training and hands-on experience monitoring bluebirds on the Wolf Trap bluebird trail.  Children under the supervision of the trained volunteer monitor are welcome to assist the volunteer while they are conducting their monitoring duties.

Interested volunteers please sign up here. For more information, contact Allen Hoffman (Friends of Wolf Trap and FMN)

Master Naturalists may receive service hours at S263, Wolf Trap Stewardship Projects.