This small falcon's population is rapidly declining in Delaware. Here's who's helping.

The American kestrel is the smallest and most common falcon in North America.

But in Delaware and throughout the Mid-Atlantic region, the species, also called a sparrow hawk, has rapidly declined.

According to the Delaware Kestrel Partnership, the Mid-Atlantic region has experienced a population decline of more than 93% since the 1960s, the greatest of any region in North America.

The falcon was listed as endangered in Delaware in 2013. In response, the Brandywine Zoo has been working to save the bird with the help of the American Kestrel Partnership, a project of the Peregrine Fund, a nonprofit organization promoting research and conservation of birds of prey worldwide.

The project, funded by mini-grants, has 62 nest boxes set up in Delaware and southeastern Pennsylvania in places like Winterthur, Delaware State Parks, Mount Cuba, Longwood Gardens and others.

Brandywine Zoo wants to gain a better understanding of kestrel populations and habitats in the Delaware Valley and also contribute its data to multiple, ongoing national research projects. The zoo and the kestrel partnership want to identify causes for population decline in Delaware and work toward providing solutions to alleviate regional population issues.

It's unclear why the population is in such rapid decline.

"That’s kind of the million-dollar question with American kestrels in general," said Jacque Williamson, curator of education and conservation for the Brandywine Zoo and the program's founder.

Likely culprits include competition with invasive species, loss of habitat due to commercial and residential development, climate change or even pesticides.

"What I do know is the sites that we have successful nesting occurs at managed grassland sites," Williamson said.

Those include Winterthur, Mount Cuba and the Delaware Nature Society.

In 2020, four nests produced chicks, with two of them being at Winterthur. 

"They’re not all that successful in Delaware right now, so we were pretty excited to hear that a couple of our nest boxes had been successful," said Chris Strand, who is the director of Garden and Estate at Winterthur and oversees the garden and natural resource teams.

"I’m kind of fascinated by it because it’s not necessarily a rare bird, but unfortunately in Delaware, there’s been a decline in their numbers."

What would a world without kestrels be like? They feast on creatures like rodents and insects and sometimes small snakes and frogs. They also prey on small birds.

"They're low on the totem pole as far as predators go," Williamson said. "But they are still a predator and play an important role."

Without the falcons, farmers may need to resort to methods of ridding prey that are more toxic to the environment.

"We have a responsibility to make sure that they don't go off on our watch, and we’re doing the best that we can to keep them around," Williamson said.

"The kestrel is almost like an indicator species," Strand said. "It’s part of the top of the pyramid. When something at the top of the food pyramid is starting to decline, you start to wonder, 'What’s going on in here?'"

The occupancy rate at the nesting boxes is 10% to 15%. Williamson said the next goal may be to start trapping the kestrels out of nesting season to better understand survival rates and migration.

Technology has been developed that allows for tracking devices to be placed on the bird. That's no easy task, considering the devices cannot be more than 2% of the bird's body weight, Williamson said. The average weight of adult kestrels is around 4.1 ounces.

Williamson said the project relies on community volunteers to nest boxes once every two weeks during nesting season, which runs from March to July. 

There's a new app, EpiCollect5, that will allow people to report kestrel sightings with geolocation tags. They can also suggest locations for nesting boxes. Good nesting box locations can be places with open farmland or grassland. Williamson said the project is looking to add more nesting boxes to Kent and Sussex counties.

At Winterthur, Strand said birding has "become this little subculture that I was not really connected with."

They've always had birders, he said, even some people on staff. But recently, they've started doing bird walks on the grounds. People can see birds like cackling geese; woodcocks; Cooper's hawks; red tails; ravens; and, of course, maybe a few kestrels.

Winterthur's mix of meadowlands and woodlands makes it a good environment for birding.

The estate and museum's participation in the Delaware Kestrel Partnership fits into its mission.

"I feel like it is a very important role that we play in making sure this habitat is intact and that we don’t do anything to willingly or knowingly destroy habitat for any of this wildlife," Strand said. "It’s partly fascinating. I’m often staring out my window here up on Farm Hill and I’m watching a fox or a bird and I realize this is kind of a luxury in a way."

Contact Jeff Neiburg at jneiburg@delawareonline.com. Follow him on Twitter @Jeff_Neiburg.