By Liz Macklin
Early this spring in Arlington’s Barcroft Park, in clearings far from busy athletic fields, volunteers installed two boxes for nesting Eastern Bluebirds (Sialia sialis). Painted white to minimize heat from the sun, the boxes sat atop tall metal poles with baffles attached to prevent hungry snakes and other predators from climbing. Wire guards were set around the entry holes to keep out prying raccoon hands.
The stage was set. Only time would tell whether any birds would take them up on the offer.
The Barcroft project is a joint effort by Arlington Regional Master Naturalists (ARMN) volunteers and the Virginia Bluebird Society, which provided the houses, protective baffles and poles.VBS President Valerie Gaffney even helped with the installation in March. Arlington County Natural Resources Manager Alonso Abugattas assisted in choosing the sites, to ensure there would be plenty of plants and insects to sustain the birds and their young.
The boxes are additions to a bird trail created in 2019 by Arlington resident and volunteer Ron Knipling, who passed away this year. Knipling and his team installed 19 small boxes suitable for chickadees and wrens (who sometimes fight over them). Bird boxes provide important habitat for bluebirds and other cavity nesting birds.
In March, ARMN volunteers Mark Colgan, Manoma Sirisena and Emily Apgar agreed to monitor the original boxes along with the two new ones. Five additional volunteers joined the team. Every week through the spring and summer, they visited all 21 birdhouses spread through the woods, recording their observations in an online log.
The first sign of bird activity was noted on April 2, when observers found evidence of chickadee nest building, including bits of moss, in four of the small boxes.
Bluebirds arrived around April 7. Their presence was announced by straw nesting material showing up in one of the two new birdboxes. The next week, monitors noticed a bluebird fly out of the same box as they approached. Inside was a cup-shaped nest, but no eggs. Anticipation mounted until April 19, when Emily peered into the box to find three eggs. Within a week the count rose to five.
By May 5, monitors found that four of the bluebird nestlings had hatched, and the fifth followed soon after. The parents stayed busy gathering insects for the brood and keeping the nest clean and safe.
During this time, eggs in the chickadee nests began to hatch and live nestlings were observed. However, in one of the boxes several chicks were missing and the remaining two were dead. The missing and dead chicks were presumed to be the victims of predation, because the smaller boxes had no protection against snakes or raccoons.
On May 19, Mark discovered a five-foot Eastern Rat Snake (Pantherophis alleghaniensis) only a foot from the bluebird box that had an active nest. As the mother bird waited in a tree, the snake paused and then slid away. A few days later, a snake was seen coiled under the baffle, unable to pass.
Birds nesting in the unprotected original boxes suffered continued losses. Chickadees were documented to have fledged successfully from only one nest. As the boxes were vacated by chickadees, House Wrens (Troglodytes aedon) built nests in their place. The wrens appeared to be equally vulnerable to predators, as monitors noted missing nestlings and a cracked egg.
To improve the smaller birds’ chances of survival, the original birdhouses will be replaced by new ones equipped with protective baffles and guards against snakes, raccoons and other predators.
For the bluebirds, success came with one of the new boxes. It is believed that five young birds fledged from that nest. On June 10, Mark cleaned out the nest, providing a chance for birds to build a second nest. Smaller birds use the bluebird boxes too, and wrens did build a nest and had three eggs, but they were apparently abandoned. The second new box never attracted bluebirds in its first year, but did produce a successful family of wrens.
With late summer signaling an end to nesting season, all of the Barcroft boxes were cleared of nesting materials and brushed clean. The season starts up again in early spring, when the team plans to add a third bluebird box. They will also remove the remaining original bird boxes and replace them with boxes that offer protection against snakes and other predators.
The long-term plan for Barcroft is to have three nesting boxes for bluebirds and three for chickadees or other small birds. “I’m really looking forward to next season,” said Emily Apgar. “My knowledge has grown by leaps and bounds, observing how the birds, particularly the bluebirds, react and interact with their environment.”