American Kestrel numbers have been dropping for 50 years. Scientists are racing to learn why and to turn around the fortunes of our most colorful falcon.
By Ronald Zigler | Published: 9/11/2017
During the four years that we lived in central Iowa, my wife and I often commuted along the two-lane highways between Des Moines, where I worked, and Jasper County, where we lived. Among the most familiar sights that we witnessed during those drives was the distinctive flight of American Kestrels hovering and hunting over the farmland. Because of the frequent sightings, I’ll always remember the vibrant coloration, bold patterning, and small stature that contribute to the kestrel’s charisma.
My interest in kestrels was further piqued when I had the chance to observe several juveniles up close at a wildlife rehabilitator in Iowa. In spite of their small size, those youngsters had the fierce look that seems to characterize all birds of prey.
However, when we left Iowa for the suburbs of Philadelphia, our kestrel sightings were no longer so common. Nevertheless, I eventually learned that a few nested regularly at the Gwynedd Wildlife Preserve, not far from my home. The preserve is managed by the region’s oldest and largest conservation organization, the Natural Lands Trust, whose mission is to protect forests, fields, wetlands, and streams in eastern Pennsylvania and southern New Jersey. The Gwynedd Wildlife Preserve is a 279-acre oasis of meadows, woodlands, and wetlands nestled among the highly developed suburbs of Blue Bell and North Wales, Pennsylvania. Managers of the preserve have created and, more importantly, maintained through controlled burnings, an ecosystem ideal for kestrels: open, short-grass habitat with cavities for nesting. Tom Kershner, the manager of the preserve, has observed kestrels every year since he arrived 17 years ago.
I frequently visited the preserve to photograph and observe kestrels. My growing admiration and curiosity for the birds inspired me to look beyond the camera lens and dig into research about the species. I quickly learned that since 1966, the kestrel population has dropped by nearly 50 percent across North America. The decline has been most dramatic in New England and the mid-Atlantic region, where the species is down 88 percent.
In 2012, The Peregrine Fund launched the American Kestrel Partnership, a program that seeks to uncover the cause of the decline and implement appropriate conservation measures. The program is comprised of a network of citizen and professional scientists who install kestrel nest boxes, monitor them through the breeding season, and report their findings on the partnership website. Staff scientists manage the information in a database that covers the bird’s expansive range (from Alaska to Tierra del Fuego) and can be safeguarded in perpetuity. To that end, the partnership provides educational tools to encourage careful and consistent monitoring, data collection, and data submission.
When I first inquired about the possibility of monitoring nest boxes, the task seemed quite daunting. At the Gwynedd Wildlife Preserve, like many other kestrel habitats, the nest box is located in an open field, on a pole that is between 8 and 10 feet off the ground — not an easy place to haul out a ladder once a week for observational purposes. In addition, opening a nest box carries the possibility of a premature escape by nestlings. As a novice, I did not want to risk this. However, the partnership had a wonderful recommendation for the task, which is much less disruptive to the birds: Mount a small GoPro-type camera on a pole and operate it remotely via a smartphone app. Thus began my experience as a citizen scientist monitoring kestrel nest boxes.
Tracking a successful nest provides considerable satisfaction. During the first season, I made weekly visits to the nest box, where I first reported five eggs. Then, four out of the five eggs hatched, and the chicks grew and fledged in four weeks. Yet such isolated incidences of success do not tell the whole story. As I mentioned, kestrel populations have been declining over the past 50 years. Evidence for the decline is underscored by the data that has emerged from the Autumn Kestrel Count in Cape May, New Jersey. From 1976 to 2016, records show a drop from more than 15,000 to less than 5,000 sightings.
Growing interest in and concern for the plight of kestrels led researchers to organize the American Kestrel Symposium at the Alapocas Run State Park in Wilmington, Delaware, in late January 2017. Sponsored by the American Kestrel Partnership in cooperation with the Brandywine Zoo of Wilmington, the goal of the symposium was to bring together individuals who have an interest in kestrel conservation. Over the course of the weekend, approximately 100 professional researchers, graduate students, representatives of state wildlife agencies, and citizen scientists from across North America discussed kestrels. In addition to describing current research and observational programs, the symposium also provided an opportunity to begin developing a single protocol and data entry format for monitoring the birds during the upcoming breeding season.
Declines Vary Regionally
The keynote speaker was John Smallwood, associate professor of biology at Montclair State University in New Jersey. Since 1990, he has been studying populations of kestrels that breed in nest boxes that he has erected in New Jersey as well as Florida. At the outset of his presentation, Smallwood addressed the question of precisely why kestrels are declining. To be sure, the decline, while nearly universal, is not uniform. The kestrel is among the most widely distributed raptors in North America and has a range that extends into South America as well, making it the most widespread falcon in the Western Hemisphere.
While population fluctuations have not been as dramatic in the Midwest, the East Coast in general and New England in particular have witnessed the most precipitous populations declines (see the chart above). In New Jersey, kestrels are listed as a species of “special concern.” In Connecticut and Pennsylvania, they are listed as “threatened,” while they are identified as “endangered” on Delaware’s endangered species inventory.
Addressing the decline, Smallwood identified four factors that may explain the population drop: West Nile virus, predation by Cooper’s Hawks, habitat loss due to degradation and development, and the use of pesticides and other pollutants. While all may play a role, Smallwood says researchers cannot identify one leading cause. More research is needed, he concludes.
It is the indeterminate cause of kestrel decline that inspired an important part of the partnership’s mission — the nest-box-monitoring program. Encouraging the establishment of new nest boxes would appear to be an important conservation measure to help kestrels. After all, habitat loss and degradation are among the factors that appear to have played a role in their decline.
Indeed, kestrels require somewhat special habitat conditions for their nest boxes, including at least an acre, if not more, of low grassland surrounding the box. When land is developed and habitat lost, kestrels as well as other cavity-nesting birds lose the natural tree snags that would otherwise provide nesting sites. Hence, when a nest box is set up and occupied, it would appear to be an important conservation measure. Unfortunately, the mere proliferation of nest boxes by itself is not necessarily going to stem the decline of this little raptor.
Chris McClure, director of global conservation science at The Peregrine Fund and until recently the director of the American Kestrel Partnership, underscored this point at the symposium. His research has found that increasing nest box opportunities may only help healthy kestrel populations or populations suffering from a lack of nesting sites. Adding more nest boxes may not be enough to help populations recover in areas where they are already declining if the causes are unrelated to nesting habitat. That’s why it’s imperative that researchers determine precisely what is causing population declines.
Another area of research presented at the symposium involved the agricultural applications of kestrel nest boxes — specifically, in fruit-growing regions. It had already been established that kestrels can play a role helping farmers with pest control because they eat insects and small mammals. Megan Shave, who recently earned a Ph.D. from Michigan State University, and MSU biology professor Catherine Lindell demonstrated that kestrels can also help farmers with cherry orchards by deterring fruit-eating birds. While insects and small rodents make up the overwhelming majority of a kestrel’s diet, the birds occasionally prey on small birds. The mere presence of kestrels and their nest boxes was enough to serve as a deterrent to birds that would otherwise consume a portion of a farmer’s cherry crop.
According to Bruce Peterjohn of the Patuxent Wildlife Research Center and chief of the federal Bird Banding Laboratory, banding data have confirmed the decline of kestrels as well as other grassland birds such as meadowlarks in the eastern United States. In addition, banding has helped establish the presence of four major populations of kestrels in North America: birds of the East Coast, the Midwest and central plains, the Rocky Mountains through Texas, and the West Coast.
The northernmost populations make the longest migrations, leapfrogging over the central populations in fall. While kestrels in the center of the continent may move shorter distances to better hunting territories when snow covers the land, the southernmost birds, such as those in Florida, are year-round residents. Each population has declined at different rates, suggesting that regionally specific factors are at work. Only additional research will clarify this.
Sarah Schulwitz, director of the American Kestrel Partnership, laid out several research recommendations that will guide scientists’ work to understand the population drop. Understanding migratory connectivity — where different populations, breed, migrate through, and overwinter — was at the top of the list and was discussed in-depth during two follow-up presentations.
Ross Crandall, a research biologist at the wildlife research and education institute Craighead Beringia South, discussed emerging studies on the use of tracking technology for kestrels. Though their small size and reliance on nest boxes present challenges with tracking, technology is improving rapidly so that within the next few years, scientists may be able to reliably track where the raptors spend their time throughout the year.
Michaela Brinkmeyer, a master’s student at Boise State University, discussed her work in creating a migratory connectivity map using genetic samples collected on the breeding, migration, and wintering grounds. Many members of the partnership have or plan to contribute genetic samples for the study, which is called the American Kestrel Genoscape Project.
In the final analysis, much work is needed to better understand kestrels and the challenges they face for survival. On a more promising note, kestrels are nonetheless resilient and adaptive birds. They have adjusted to more urban settings when buildings provide nesting cavities adjacent to areas in which prey is abundant. It is my hope that in the coming years, we will better understand the biological and environmental factors that are affecting kestrel populations throughout North America. In the meantime, anyone who wants to assist with the research and conservation of our most colorful falcon is encouraged to visit the website of the American Kestrel Partnership at http://kestrel.peregrinefund.org. It is a great resource with a wealth of information for all concerned birders and emerging citizen scientists.
Ronald Zigler is an associate professor of educational psychology at Penn State Abington and an amateur wildlife and bird photographer. He also wrote about Otto Armleder Memorial Park in Cincinnati, Hotspot Near You No. 251.
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