The Plight of the American Kestrel

Can these boxes save a disappearing species?

(This article was originally published here)

As the sun stretches above the horizon, warming the eastern slopes of Mount Diablo, an American kestrel perches in the trees. Like a statue, it motionlessly scans the golden foothills, waiting. As the rising continues to rise, illuminating the hillside, adding crisper details to the blades of grass that stretch across the hill, everything appears still.

Quietly, a western fence lizard emerges from the grass, crawling onto a rock to bask in the morning heat after the cold night—a fatal mistake. With one swift movement, the kestrel dives down from the tree—much like how an Olympic swimmer dives into a pool to race—and snatches the lizard from the rock with its sharp talons. Before the lizard has time to understand what happened, the kestrel delivers a kill-bite on the back of its head. The kestrel will take its newfound breakfast back to its nest box to eat.

Life for the kestrels in the Diablo Range is different than it was a few decades ago. It has grown lonelier. A mystery is lingering in the air that scientists haven’t figured out yet. Although the birds are skilled hunters, they're disappearing across the country.

The Decline of the Kestrels

Throughout the 20th century, many bird population numbers were falling at staggering rates. The pesticide DDT thinned the eggshells of birds like bald eagles, peregrine falcons, and ospreys, to the point where when the parent would land on the egg, they’d crush their unborn baby. Habitat destruction and powerlines helped lead to the decline of other notable birds like the California condor. Since 1968, the American kestrel population has declined by 69 percent in coastal California, and still, scientists don’t know exactly why their numbers are still dropping.

Like the peregrines and bald eagles, kestrels are negatively affected by DDT. Thanks to the visionary work of Rachel Carson, DDT was banned in 1972. While the bald eagles and peregrines have rebounded, the kestrels have not. In what is somewhat a last-ditch effort, kestrel nesting boxes are being set up across the nation in hopes that it’ll either help better stabilize the population, or lead scientists to discover what’s happening to kestrels.

The American Kestrel Partnership—as they describe themselves, “a network of community and professional scientists working to collaboratively understand kestrel demographics and advance kestrel conservation”—are calling for bird lovers and watchers alike to set up and monitor nesting boxes across the country. The idea is that the data collected will reveal what the missing link is between kestrels and their declining population. The boxes may help the declining population by providing safe shelter, but if the kestrels are not vanishing because of habitat loss, the boxes won’t do much.

An American kestrel (Falco sparverius) in flight.

Unlike other birds, kestrels don’t make nests, but rather nest in cavities that they find—such as holes made by woodpeckers, tree cavities, barn roofs, and so forth. Kestrels are, however, very picky about where they live. A perfectly placed nesting box won’t ensure that a kestrel will move in.

Placing a nesting box requires strategy that is comparable to making a chess move. It ought to position the bird in a way where it can attack and hunt prey. At the same time, it needs to have a defensive layer to it. For instance, it should be high enough off the ground where it’s safe from lurking predators.

Making New Homes

After a turbulent week of rain and wind, the sun broke out of the clouds. With the new weather window, Save Mount Diablo Land Programs Director Sean Burke was hoping to install some nesting boxes he recently built before mating season began.

I met him at Smith Canyon—a protected property located on the eastern side of Mount Diablo. Stepping out of my car, he was already pointing out some kestrels flying overhead.

“They’re pretty metal creatures,” he explained. “They can see ultraviolet light, they’re like the bird version of the terminator.”

Sean walking out, scoping a cite for a nesting box.

Sean and Save Mount Diablo have been working to protect kestrels for some time now. Last year, they released kestrels back into the wild that were rehabilitated by the Lindsay Wildlife Experience. They released four at Mangini Ranch, and four at Curry Canyon Ranch.

Carrying a ladder in one hand, and a nesting box in the other, Sean hiked up a steep hillside until he found a spot he liked. Using a compass, he angled the box to face eastward (this way the sun will warm up the box faster in the morning). Using straps to protect the tree, he fastened the nesting box up above.

The second kestrel box, however, would be more difficult to place. Wanting to stretch out the distances between the boxes, we hiked to find a new stop. An enormous oak tree stood on the top of a hill, it looked like the equivalent of a 5-star hotel for the lucky kestrel resident. Sean, however, looked disappointed at the base.

“Bobcat scat” he muttered, looking at the fresh feces at the base of the tree. He was worried that this could be a popular spot for bobcats, and that they could climb their way into the kestrel box. Soon enough, we found another safer spot to hang the nesting box.

A nesting box strapped to a tree.

The future for the American kestrels still remains uncertain. There’s still reason to be optimistic, as more nesting boxes are appearing across the country. As for our nesting boxes, they’ll hopefully provide a good home for kestrels to watch the sun rise from the Diablo foothills. They can stay there perched, hunting western fence lizards along with other insects and small rodents. And maybe sometime in the near future, they’ll be able to thrive in the Diablo region without worry.