On a humid afternoon in late May, Cliff Boucher walks the perimeter of his ten-acre property in Schoharie County, New York, opening twenty-three nest boxes in sequence. He carries a small mirror on a telescoping handle, a clipboard, and a flashlight. He spends approximately ninety seconds at each box.
What he is doing is participating in NestWatch, the Cornell Lab of Ornithology's nest-monitoring program. He has done this every spring and summer since 2006.
NestWatch began in 2007 as the successor to several older nest-record schemes, including the Cornell Nest Record Card Program, which itself dated to 1965. The merged program asks volunteers to locate active nests, visit them on a regular schedule, and record what they find.
The data of interest are reproductive outcomes — when eggs were laid, how many, when they hatched, how many fledged. These metrics, summed across thousands of nests and species, allow researchers to track reproductive success across years, regions, and habitat types.
The protocol is more rigorous than it appears. Volunteers must check nests on a schedule — typically every three to four days — that captures the important transitions without disturbing the nesting birds. Visits must be brief. Volunteers must not visit during inclement weather, during the period when adults are likely incubating cold eggs, or when fledglings are near departure and might prematurely leave the nest.
Volunteers must also accurately identify what they see, which is harder than it sounds with eggs and nestlings of similar species.
Cliff Boucher's twenty-three boxes host, in a typical year, two clutches of eastern bluebirds, three of tree swallows, two of house wrens, and a varying mix of black-capped chickadees, white-breasted nuthatches, and house sparrows. He has, across nineteen years of monitoring, documented the fledging of approximately twenty-six hundred nestlings.
The NestWatch database currently contains records of approximately five hundred and twenty thousand nesting attempts across over six hundred species. The contributing volunteer base in any given year is approximately ten thousand active monitors.
What the dataset has shown, in aggregate, has tracked the broader patterns visible in other monitoring programs. Many cavity-nesting species — bluebirds, chickadees, swallows — have stable or increasing populations in monitored areas, in part because the boxes themselves are providing nesting opportunities that compensate for the loss of natural cavities. Open-cup nesting species, which cannot benefit from nest-box programs, have generally declined.
More specifically, the NestWatch data have allowed researchers to track the response of breeding birds to climate change at fine temporal resolution. A 2019 paper led by Robyn Bailey at the Cornell Lab analyzed approximately three hundred thousand nest records and documented that several common species — tree swallow, eastern bluebird, house wren — have advanced their average egg-laying dates by approximately five to seven days since 2000. The advance correlates strongly with regional temperature trends.
Whether this advance is sufficient to track the underlying changes in food availability is the more troubling question. The tree swallow finding has been particularly studied. The species depends on aerial insects, whose emergence is also shifting earlier. The match between hatching and insect peak has historically been tight. The current data suggest the match is loosening — that the birds, despite advancing, are not advancing fast enough.
Cliff Boucher noticed this himself, in his own way, some years ago. He keeps a personal record of his nest data alongside what he submits to NestWatch, and the long-term pattern at his property has been that nestling tree swallows in early broods are heavier than nestling tree swallows in later broods, but the early broods themselves are now hatching slightly earlier and the nestling weights are slightly lower than they were in his early years of monitoring.
He is not a statistician. He is a retired electrician. But he has been watching the same boxes for nineteen years and he knows what he is seeing.
The discipline of nest monitoring is not for everyone. It requires regular visits across the breeding season — typically from late April through early August in the Northeast. It requires comfort with disturbing, briefly, the most vulnerable phase of a bird's life cycle. It requires honesty about failures.
Cliff documents nest failures meticulously. House sparrow predation. Black rat snake predation. One particularly grim June morning in 2018 when a black bear took out three boxes in sequence. He records these outcomes the same way he records successful fledging.
The NestWatch database, accordingly, is one of the few large-scale records of nest failure rates across North American breeding birds. The data show that nest predation rates have increased modestly over the past two decades for several species, consistent with what some other studies have found.
What predators are responsible is harder to determine. The volunteer typically arrives at a nest after the predation has occurred, finding broken eggshells, missing nestlings, or a disturbed nest. Forensic identification of the predator is rarely possible without camera traps.
Several NestWatch participants, including Cliff, have begun installing motion-triggered cameras on selected boxes. The footage is uploaded to a separate research project at the Cornell Lab. The results, when they come, will help calibrate the predation records.
Cliff's boxes today contain five active nests — three eastern bluebird clutches with eggs, one tree swallow clutch with day-old nestlings, and one house wren nest with eggs being incubated. He records the status of each, the count of eggs or nestlings, the apparent health of the chicks where visible, and any environmental notes. He closes each box gently.
The whole walk takes ninety-four minutes.
He will repeat it on Tuesday.
Across the country, ten thousand other monitors are walking similar routes — Sandy Falsetti's chickadee boxes in Vermont, Marcus Yeo's tree swallow line at a Saskatchewan farm, Lupita Carrasco's purple martin colony in San Antonio. Their notes will accumulate into the database that, sometime in 2027 or 2028, will produce the next major NestWatch analysis paper.
The paper will probably contain phrases like long-term decline, advancing phenology, regional heterogeneity. It will, less visibly, contain the work of Cliff Boucher and ten thousand others, walking their box lines on humid afternoons in late May.
