Songbirds Find Nesting Success Thanks to HCT Volunteers

Tree swallow parent on a fly-by feeding (photo: Sarah E. Devlin Photography

“There is a sumptuous variety about the New England weather that compels the stranger’s admiration — and regret.”
~Mark Twain, during an 1876 speech to the New England Society.

Story by Susanna Graham Pye

As Cape Codders, we know the truth in Twain’s words and are experts at riding the meteorological roller coaster that is spring on this ocean-cradled spit of land.  

No matter how unpredictable our weather might be though, spring arrives with unmitigated certainty upon the wings of the native birds that winter here alongside the many migrants who make their ways to our shores from far-flung corners of the globe. 

On icy cold late February and early March mornings, rain, snow or sun, riding gale winds or soft breezes, the chickadees and titmouses amorously call to one another, robins warble, Carolina wrens shout. A symphony of song rises through the nesting season, building into a joyous crescendo that ceases only when fledglings fly and summer starts to wane. Approximately 150 species of birds nest along the Cape’s shores, in its forests, and marshes.

For fourteen years, the Harwich Conservation Trust (HCT) has been tracking the success of some of the Cape’s avian residents with its nest box

Chickadee flying (photo: Janet DiMattia)

monitoring project managed by HCT volunteers. The volunteers typically visit nestboxes on a weekly or bi-weekly basis from March through July in all types of weather. They check for nesting starts, type of species in each nestbox, number of eggs, number of hatchlings, and ultimately the number of fledglings. A fledgling is a juvenile bird that actually  takes wing from the nest to begin its own life cycle.

Volunteers also document the fate of each nest whether as a success with at least one young fledged, or a failure due to predation, unhatched clutches or unknown causes. Volunteers are careful not to check nests shortly before fledging during a period of time when disturbing the nest could cause the young to leave the nest before they are ready to fledge.

The volunteer nestbox monitors have noted interesting findings about the nesting success of several species. For example, since 2008, volunteers recorded a total of 3,423 birds fledging among the five species at three Harwich conservation areas:

  • bluebird: 558 fledglings
  • house wren: 896 fledglings
  • tree swallow: 1,596 fledglings
  • chickadee: 250 fledglings
  • titmouse: 123 fledglings

Because of the state and federal Covid-19 stay-at-home advisory, the volunteers have paused their spring site visits and will re-evaluate in June. The bird boxes are built for native tree-cavity nesters such as Eastern bluebirds, tree swallows, black-capped chickadees, titmice, and house wrens. HCT’s songbird nesting success project has three primary goals: to improve local nesting success for selected cavity-nesting songbirds, help provide data to Cornell University’s NestWatch program, and to involve local residents with citizen science.

Female bluebird with food for her family (photo: Janet DiMattia)

“When you walk the trails at HCT’s Robert F. Smith Cold Brook Preserve and you see the bright feathers and hear the singing of the bluebirds, it’s both relaxing and inspiring. We’re grateful that HCT volunteers have been documenting the nesting success of several species and we appreciate our partnership with the Cape Cod Bird Club at the outset. When the stay-at-home advisory lifts, the volunteers are eager to continue their citizen science endeavors to support greater nesting success,” said Michael Lach, HCT Executive Director.

The nesting success rates of our native songbirds, without protection or monitoring, have been negatively affected by two primary factors, which are issues for many Cape flora and fauna: habitat destruction from development and the introduction of non-native species.

For cavity nesters, the Cape’s development of open spaces has whittled away at nesting options. The dilemma isn’t merely clearing land for buildings, but with all that often comes with it:  homeowners whose tidy yards are cleaned each spring of underbrush and deadwood, upgraded with cost saving synthetic replacements for old wood posts and fences, all decorated with pretty gardens and green lawns kept insect free with the use of pesticides (though pesticide and rodenticide use is falling as people become more and more aware of the dangers, especially for hawks, owls and other raptors who consume poisoned rodents).

Chickadee takes flight (photo: Janet DiMattia)

And then there are English house sparrows, a non-native, invasive species that arrived in the United States during the late 19th century, who pose a threat. House sparrows were first introduced in Brooklyn, New York, released with good intentions by those trying to fight the spread of inch worms that were eating trees. In fewer than 50 years, the little bird’s range in the country had spread to the Rocky Mountains.   

These tenacious little birds, whose steady cheerful chirp provides a common soundtrack in more urban settings, compete for the same nesting spaces. House sparrows aggressively occupy nesting cavities, and often kill nestlings and even adult birds of other species to take over a nest box.

Currently volunteers monitor 88 local Harwich nest boxes. The birdhouses, designed to exacting detail to protect against invasion from aggressive, non-native European starlings, are located on designated bluebird trails found at HCT’s Robert F. Smith Cold Brook Preserve as well ast the town-owned Thompson’s Field and Texeira Conservation Areas. There are 46 nest boxes at the Robert F. Smith Cold Brook Preserve; 14 at Texeira; and 28 at Thompson’s Field. Volunteers record data on the species, number of eggs, nestings, and attempt to determine the fate of each nest. Nest boxes are being added this year at HCT’s newest preserves, Cornelius Pond Woodlands and Muddy Creek Headwaters.

Over more than a decade of observation, HCT volunteers have documented 1,067 nesting attempts. Tyler Maikath, HCT’s Outreach and Stewardship Coordinator, says gathering the amount of data that has been collected would be impossible without the volunteers.

“Our data shows that the House Wren population is strongly increasing at Cold Brook Preserve and Thompson’s Field,” Maikath said. 

While nesting attempts for House Wrens increased nearly five-fold in the past decade, Eastern Bluebird attempts declined in the same locations by more than half. Maikath said the thought is House Wren behavior could be having a negative impact on the bluebirds’ success. House Wrens tend to take over the nests of other cavity-nesting species.

“We have not yet done any analysis regarding whether this trend is statistically significant,” he said, adding that future research opportunities include hypothesis testing

Nesting tree swallows (photo: Janet DiMattia)

to determine if there are statistically significant trends in the data that have been collected by the volunteers.

Other factors affecting bluebirds are the severe winters between 2013 and 2015.

Volunteer Judith Bruce called the experience of helping the project “magical and mystical.”

“Week after week I would find empty boxes,” she described. “Then suddenly a stick, or a blade of grass. Then on the next visit, the start of a nest.”

The nests, Bruce said, were built quickly sometimes, which could be only a few days. No matter the speed of construction, “each visit brought the wonder of what might be found when the box was opened.”

Bruce said she marvels at the consistency with which the birds construct their nests.

Bluebirds pair up at HCT’s Robert F. Smith Cold Brook Preserve (photo: Janet DiMattia)

Bluebirds build grass or straw nests and lay bright blue eggs. Tree swallow nests look the same as bluebird nests but they line their nests in beautiful soft, white, large feathers and lay pure white eggs,” she said. “House wrens build their nests of sticks and can fill a box completely to the top making it almost impossible to peer inside. Their tiny eggs are beige with brownish speckles. Chickadee and Titmouse nests are the softest moss with a perfect rounded egg cup often lined with animal fur or seed tufts (usually chickadee) or cut up pieces of leaves (usually titmouse) and often with a top covering of more soft moss. Their eggs are similar in size and color to house wrens.”

Uplifting moments are checkered with heartbreak, Bruce said, witnessing the aggressive behavior of competing birds or seeing nests lost to storms. 

Tree swallows (photo: Janet DiMattia)


“But the wonder of nature is always present,” she said. “And the nest box monitoring gives us an opportunity to be inspired and fascinated to help us all gain an appreciation for how each bird or bug or animal or plant fits into the complex ecological whole.”