Could a population surge of Cooper’s hawks limit kestrel habitat? What is happening to the kestrels’ winter habitat? In the spring, do agricultural fields lure kestrels to nest, letting them down when the land changes seasonally with planting or harvesting? Could kestrel decline be linked to insect decline? Are rodenticides, poisonous rats and mice a threat to all birds of prey that eat mice, are kestrels of special concern? What are the effects of neonicotinoids, a particularly potent insecticide? What about the effects of climate change?
Many kestrel experts think it’s a combination of reasons.
“It’s just everything,” said Jean Francois Therrien, senior scientist at Hawk Mountain, a bird of prey conservation group. “Many factors play a small role, but add to the declines we’re seeing.”
Dr. Smallwood agrees, but he still has prime suspects.
“If I may be allowed one word: grasshoppers.”
Popping up keeps finding
Sure, kestrels also eat rodents and lizards. Dr. Smallwood is seeing debris in the nests, which suggests they are feeding more songbirds than before. But he thinks lack of insect prey is a major problem, a theory that could be bolstered by the early results of an ambitious modeling effort that will try to solve the mystery of declining kestrels once and for all.
Funded by the United States Geological Survey and the US Fish and Wildlife Service, the project is a partnership of more than 50 collaborators, including scientists from universities, conservation groups, states, Native American tribes, and the federal government. Researchers are in the process of establishing and testing continent-scale models. One parameter that appears to be declining over time, the researchers say, is the survival of young birds in the summer.
“It’s not a firm conclusion yet because we haven’t finalized the modeling,” said Brian Millsap, who recently retired as the national raptor coordinator for the Fish and Wildlife Service and is affiliated with New Mexico State University. “But it seems like a finding that pops up no matter how you set the pattern.”
