American Birding Podcast



The How and Why of Urban Cooper’s Hawks

It sounds strange to say that Cooper’s Hawks were once relatively unusual in urban and suburban settings. The dashing raptors are ubiquitous now, even in the most developed landscapes, and this population boom is certainly inverse to the fairings of so many other North American native birds. Why, then, does this species thrive in places where others do not?

Researchers from the US Fish & Wildlife Service, partnered with the New Mexico Game and Fish Department and New Mexico State University, are trying to answer these questions and more in the hopes that it will provide some insight into not only Cooper’s Hawk biology, but raptors in general.

A young Coopers Hawk on a manmade structure, an increasingly common sight continent-wide. Photo by Manjith Kainickara via flickr

A young Coopers Hawk on a manmade structure, an increasingly common sight continent-wide. Photo by Manjith Kainickara via flickr

Science Daily recently reported on this massive 6 year Cooper’s Hawk study in New Mexico:

“What we’re studying is the population biology of the Cooper’s hawks,” said Brian Millsap, national raptor coordinator for the U.S. Fish and Wildlife Service. “Their basic biology is similar to a lot of other raptors and their population biology is not that different from golden eagles, a species of great concern for us, but which are scarcer and therefore a lot harder to work on.”

What began as a Fish and Wildlife Service study, Millsap has carried forward for almost six years, making the study his Ph.D. topic at New Mexico State University. He and his team of researchers have banded almost 500 hawks, and tagged close to 100, which are monitored with radio tracking. Each year the tram tracks the fate of 50-80 nests.

The research focus on a number of questions both unique to Cooper’s Hawks and applicable to raptors in general. For instance, most raptors show pronounced sexual dimorphism, with the females much larger than the males. But precisely why this is the case is an open question. It’s suspected that it’s the result of role partitioning in breeding pairs. Smaller males are better hunters and can provide better for chicks in the nest, while larger females can lay larger clutches of eggs.

And of course, the question of why Cooper’s Hawks in particular are so well suited to an urban lifestyle likely has to do with the rapid expansion of White-winged Doves in the west. More, as the long-term climate model changes, this adds interesting wrinkles into how the birds react.

In drought years, doves seem to concentrate in the urban areas where food and water are plentiful. However, in wetter years like this year, food and water are plentiful everywhere, and doves are more dispersed. This leads to less food for the urban hawks, and researchers are seeing a potential issue with food, for the first time this year.

It’s an interesting look into a common species, showing us how much we have to learn about species that we seem to know well.