Why is America’s Smallest Falcon Disappearing?

KEMPTON, Pa. — One of Mother Nature’s tiniest, yet fiercest hunters faces an uncertain future. The American Kestrel, North America’s smallest and most common falcon, has been steadily declining across the continent since the 1970s. Despite years of research, scientists have struggled to identify exactly why these colorful raptors are disappearing.

For the first time, researchers have mapped out survival rates of American Kestrels during different seasons and life stages, following both adults and juveniles across multiple sites from Pennsylvania to Florida.

The research team, led by Dr. Mercy Melo of Hawk Mountain Sanctuary Association, tracked 202 kestrels using radio telemetry between December 2020 and December 2022. Melo collaborated on the study with experts from The Smithsonian, and the University of Massachusetts-Amherst. Their paper, published in the Journal of Raptor Research, reveals surprising patterns about when and where these birds face their greatest survival challenges.

The American Kestrels’ Winter Challenge

American Kestrels are familiar birds to many outdoor enthusiasts. Males display striking slate-blue wings with rusty backs, while females show warm, rufous coloration. Both sexes of the falcon can often be spotted hovering over grasslands or perched on roadside wires, scanning for prey. Their distinctive head-bobbing behavior makes them relatively easy to identify.

One of the study’s most important revelations concerns winter survival. Kestrels overwintering in Pennsylvania showed notably lower survival rates compared to those wintering in Florida. This difference might seem small on paper (0.9316 weekly survival in PA versus 0.9881 in FL), but it translates to dramatically different outcomes over an entire winter season. After just 10 weeks, a Pennsylvania kestrel population would be roughly half the size of a Florida population that started with the same number of birds.

This survival difference highlights a fundamental tradeoff in kestrel life history: risk migration to reach more favorable winter conditions, or stay put and face harsher winter challenges as a resident bird.

Males Face Higher Mortality Risks

The study revealed a clear survival gap between male and female kestrels. Males died at higher rates than females throughout the year, but this difference became especially pronounced during the coldest months. To put this in perspective: if you followed 100 female kestrels through a typical winter month, about 96 of the falcons would survive. Follow the same number of males, and only about 90 would make it through that same month.

Over the course of an entire winter, this seemingly small difference compounds dramatically. By the end of the season, a population that started with equal numbers of males and females would have significantly fewer males remaining. Researchers believe this survival gap likely stems from the smaller body size of male kestrels. Being roughly 10-15% smaller than females makes males more vulnerable to cold temperatures and food shortages during harsh winter conditions. Their smaller bodies simply can’t store as much fat for insulation and energy reserves, putting them at a disadvantage when resources become scarce.

Young Kestrels Surprisingly Resilient

The research team made an unexpected discovery about baby kestrels that contradicts what scientists have long believed. Conventional wisdom has held that the first few weeks after leaving the nest are extremely dangerous for young birds of prey, with many not surviving this vulnerable period. However, this study found just the opposite.

When tracking newly fledged kestrels across different study sites, researchers discovered that between 94% and 100% survived each week after leaving the nest. In some locations, not a single juvenile kestrel died during the entire tracking period. Out of 146 young kestrels tracked, only 8 died — a survival rate far higher than previous studies had found.

This surprising resilience of these young falcons suggests that the population decline affecting this species likely stems from challenges faced by adult birds rather than high mortality among youngsters.

Human Factors Play a Major Role

Kestrels’ adaptation to human landscapes by nesting in building cavities or using artificial nest boxes has made them one of the most visible raptors. Yet their close association with human environments may come at a cost, as shown by the high proportion of human-related mortality documented in this study.

When kestrels did die, the causes varied by age group and season. For adults, most deaths (70%) were attributed to human-related causes such as collisions with vehicles or entrapment in buildings. Natural causes, including predation by other raptors, accounted for the remaining 30%.

The timing of mortality events followed clear patterns. All adult deaths from entrapment in buildings occurred during breeding season, while deaths from other causes happened during the nonbreeding season.

Study authors emphasize that their results “ultimately direct conservation and research efforts toward adults during the nonbreeding season in northeastern North America, which may represent an exceptionally vulnerable stage marked with low survival rates.”

Transforming Conservation Approaches

As climate patterns shift and development continues to transform landscapes, understanding how kestrels respond to these challenges throughout their annual cycle becomes increasingly important. Studies like this one provide the scientific foundation for designing effective conservation strategies that address the specific threats kestrels face during different life stages and seasons.

By identifying the nonbreeding season as a particularly vulnerable time for adult kestrels in northeastern North America, conservationists can focus efforts on improving winter habitat conditions and reducing human-related threats during this critical period for the falcons.

“Understanding the factors influencing the American Kestrel population decline will help kestrels but will also improve our understanding of other declining species,” Dr. Melo says in a statement. “We hope [our study] entices researchers to adopt collaborative approaches across geographical regions.”

The researchers acknowledge that much remains to be learned about kestrel survival during the migratory period itself, which couldn’t be captured in this study due to the limitations of VHF transmitter battery life. They suggest that future studies utilizing newer tracking technologies capable of monitoring birds throughout migration would fill this remaining knowledge gap.

For now, the message is clear: saving American Kestrels requires a seasonal approach to conservation that recognizes the unique challenges these birds face throughout the year. By focusing protection efforts on adult kestrels during the nonbreeding season, particularly in northeastern North America, conservation biologists may be able to address one of the most significant factors contributing to the species’ decline.