*A note on all photos* All birds handled for the purpose of scientific research under a federally authorized Bird Banding Permit issued by the U.S. Geological Survey and in accordance with all state permitting requirements.
If you were to see an American kestrel perched on a farm fence, you might think, “What a little cutie!”
Weighing approximately four ounces, with a wingspan of about 10 inches, kestrels are really not much bigger than a mourning dove. Not to mention their plump plumage, colored in complementary blue-gray and burnt orange, makes them look almost like a friendly little plush doll.
But don’t be fooled.
These tiny raptors are precise, calculated predators, silently swooping in to hunt field mice, insects, and other small prey.
“The adults are pretty wild,” said Jim Arbruster, lead biologist at the Vermont Institute of Natural Science (VINS). “They’re about as aggressive as you’d expect a raptor to be that you’re plucking from its nest.”
Yet Jim and the team at VINS are dedicated to protecting these birds not only because of their grace, beauty, and incredible capabilities, but also because they provide an essential ecological service in Vermont’s rural landscape.
“In their ecosystem, they’re the predator, right? So they are doing that rodent control.” Said Jim, “they’re definitely providing that ecosystem service for those farmers.”
And just like any ecosystem, the intricate food web has a delicate balance. Remove one link, and there can be ripple effects throughout the system.
Over the course of VINS’ five-year study, population trends in Vermont and across the country have shown a decline in American kestrels.
Fortunately, VINS is not alone in its efforts to support these birds.
Working with landowners across the state, the team has established a network of nesting boxes—small wooden birdhouses that provide fledgling habitat while also serving as important tools for ecological monitoring.
Working closely with landowners, Jim and his team regularly visit these nesting boxes. Sometimes, their visits begin with an excited call from a landowner letting them know that a kestrel has arrived.
During the nesting season, the researchers carefully capture adults and fledglings so they can monitor the population and collect essential data about the birds’ health.
Recently, a potential threat to raptors and predators in general has come into the spotlight and emerged as focus point of VINS kestrel health monitoring: anticoagulant rodenticides.
These poisons are widely used in urban, rural, and agricultural settings, but their effects on predators like kestrels are still largely unknown.
Because rodenticides are often marketed as a quick and easy solution for controlling mouse populations, they can be an appealing option for farmers and landowners.
But there is a catch.
“[Rodenticide] doesn’t necessarily kill the rodent right away,” Jim explained. “They will ingest the toxin and then make it an easy picking for the raptor.”
That creates a potential pathway for the toxin to move up the food chain. A kestrel may consume a poisoned rodent and, in turn, be exposed to the same chemicals intended to control the rodent population.
The direct effects of these compounds on kestrels and other birds of prey are still largely unstudied.
Further investigation is needed, but a preliminary literature review cited by the Vermont State Legislature and provided by the nonprofit Protect Our Wildlife found that anticoagulant rodenticides can result in “compromised immune and circulatory systems and abnormal clotting mechanisms.”
Although this information was presented to state legislators last year, there was not enough hard data available at the time to impose a statewide ban on the use of anticoagulant rodenticides.
That’s why Jim and VINS set out to continue their research with support from a STRIVE STaRS award. The project will collect blood samples from kestrels and establish a health-monitoring system to better understand the bioaccumulation of toxins associated with anticoagulant rodenticides.
Fortunately, the landowners who work with VINS to establish nesting sites are enthusiastic about welcoming kestrel families to their properties.
“Almost all of our landowners have that mindset of, like, ‘I’d rather have a kestrel than rodenticide.’”
And there are other ways landowners can encourage kestrels and other natural predators. In addition to providing adequate nesting boxes, promoting native plant species can help attract raptors by restoring habitat and creating abundant food sources throughout the food web.
So far, the five-year program has been a huge success. While kestrel populations continue to show signs of decline, the VINS nest-box network successfully fledged 83 birds this year, helping to slow the decline in Vermont.
But the ultimate goal of this work goes beyond protecting a single species. It’s about building the scientific evidence needed to inform policy.
By demonstrating how these poisons can affect raptors and other predators, researchers can equip policymakers with the data necessary to understand the scope and severity of the problem.
Until then, Jim and his team will continue working with landowners to educate communities and demonstrate that alternatives exist.
“We’re continuing to add new boxes. We’re making those landowner engagements and connections. And then, from that, we hope to be able to get the information that we can give to the state—to provide more information to decision-makers and say, ‘Hey, this is a problem.’”
Story by Devan Monette, Photos provided by Jim Armbruster
*A note on all photos* All birds handled for the purpose of scientific research under a federally authorized Bird Banding Permit issued by the U.S. Geological Survey and in accordance with all state permitting requirements.
