I recently got a message from The Raptor Center (TRC) at the University of Minnesota about a concern it has for the American kestrel, sometimes known as the sparrow hawk. In the last 20 years, TRC has noticed a marked recent decline in the number of kestrels admitted for their care from about 100 in 1999 to about 20 in 2019, or an 80 percent decline. On the surface, that data looks like good news until one investigates the reasons behind the decline.
The TRC’s local findings mirror what is reflected in the kestrel population as a whole. It is estimated that kestrel numbers have dropped nearly 50 percent in the United States in the last 50 years, an alarming figure to say the least. I too have noticed a decline over the years in my work and observations.
Many years ago, when kestrels were more numerous, I could often find them every few miles hunting in open country while perched on fence posts, wires and utility poles along roadsides, especially during migration. I used to patrol back roads for kestrels with my bal-chatri traps, a hardware cloth trap with nylon nooses on the outside and a mouse for prey on the inside, to attract and catch kestrels for banding.
When I spotted a kestrel, I would slowly drive down the road, carefully open the car door and drop a trap or two along the road shoulder within view of hunting kestrel(s). I continued down the road for about 50 to 100 yards where I turned around, stopped, waited, and watched for a ‘hit’. If a bird was hungry enough, it would swoop down on the trap, try to grab the mouse with its sharp talons, but sometimes getting its toes or foot caught in the nooses. Once the bird was securely trapped, I would drive back to the trap, capture the kestrel in my hands, and remove it from the nooses. Then I took biological measurements, banded it, and released it unharmed. Of course, I had to have a Federal bird banding permit to do this research. At that time there were lots of kestrels to band; not so nowadays. Banding has shown that kestrels are not long-lived, less than five years for wild birds with the oldest banded bird being 11 years and 7 months old.
Over the years I noticed a subtle, but real decline in kestrel observations along Wisconsin roadsides since about the mid-1980s. Other birdwatchers, who have been around for a few years like I have, also began remarking about seeing fewer and fewer kestrels. It became apparent that kestrels were disappearing from our open, grassy landscapes, something the general public wouldn’t normally be aware of. That is why I am writing this article—to alert the public of the potential of losing one of our most iconic bird species from the countryside.
Once I started looking into what was happening, I was alarmed. According to the Spring 2019 issue of Living Bird Magazine, data collected from migration counts, the U.S. Geological Survey’s Breeding Bird Survey, and nest-box monitoring programs confirmed declines nearing 50 percent in the last 50 years of American Kestrel populations in North America. Some northeastern states are experiencing even larger losses. It has become necessary to list kestrels as endangered or threatened in four northeastern states, and 21 states list them as a species of concern.
Whether birdwatchers or not, we all need to be concerned about a decline of that magnitude because it signals that something is drastically wrong with the health of our environment. In addition, there has also been a puzzling decrease in kestrel body size in recent years, possibly related to environmental stress factors.
There does not appear to be just one reason for the decline, but more likely multiple, cumulative factors. These factors include habitat loss, pesticide use, West Nile virus, insect declines, commercial agriculture practices, predation, and loss of natural cavity nesting sites. Some would say it is a perfect storm explaining the decline of the magnitude this species is enduring.
The American kestrel, about the size of a mourning dove, is the smallest falcon we have. They nest in old woodpecker holes in dead trees, natural tree hollows, and cavities in barns and wood buildings. Old and dead trees, and old barns, are becoming scarce in kestrel country. Plus, kestrels must compete with other cavity-nesting birds and squirrels for the dwindling number of potential nest sites.
Fortunately, kestrels will readily nest in artificial nest boxes. In fact, most kestrel conservation efforts across the nation focus on encouraging bird lovers to build kestrel nest boxes. If you would like to build some kestrels nest boxes, the plans can be found at this link: https://hub.peregrinefund.org/system/files/posts/AMERICAN%20KESTREL%20NEST%20BOX%20PLAN%20%26%20CONSTRUCTION%20NOTES%20-%202015%20_%20Master%20Copy.pdf
Much of the kestrel’s preferred open grassland habitat has been and is being developed or turned into agricultural use with few fence rows, less plant diversity, and increased pesticide use, all of which affect kestrel prey populations they need to survive.
A typical summer kestrel prey menu includes insects, snakes, small birds, mammals, even amphibians and reptiles. Kestrels will dine on just about anything hopping, crawling, skittering, jumping, flying, or burrowing that they can catch. Often, kestrels can be seen helicoptering over fields looking for prey.
While kestrels do feed on small rodents and birds, most of their diet is made up of earthworms and large insects like grasshoppers, according to long time kestrel researcher David Bird. Bird says pesticides may be making it more difficult for kestrels to find their preferred food source. Indeed, recent studies suggest that insecticides, particularly neurotoxic insecticides designed to kill insects by attaching their nerve cells, have negative consequences that travel up the food chain. This affects a wide range of insect-eating birds like kestrels, swifts, swallows, purple martins, loggerhead shrikes, whippoorwills, nighthawks, among others — many of which are also declining.
Fortunately, the good news is that the kestrel decline appears to be finally leveling off, at least for now. However, the decline is so serious that it has caught the attention of wildlife agencies, ornithologists, conservationists, and scientists across the country. Research is now underway to identify causes and to find solutions for this decline before it is too late to save one of our most popular and once most abundant small falcons in North America.
You can help American kestrels by limiting pesticide use, planting native vegetation, encouraging insects, putting up nesting boxes, and keeping cats inside.