Last month’s column on the clever antics of crows and jays elicited more reader responses than any column in recent months. Thanks to all of you who sent me stories and other responses. Your reaction prompts me to share more on the topic of clever birds.

Take the Black-capped Chickadee, a sprightly black and white bird that commonly visits seed feeders. Have you ever counted the number of “dees” on the end of a chickadee’s “chick-a-dee-dee-dee” call? If you have, you know that sometimes chickadees give just a half-hearted call with two or three “dees” at the end. Other times, they belt out this call with up to five “dees” at the end.

For clarification let me back up a moment. Songbirds vocalize for several reasons and most have both a song and a call. Songs, used mainly in spring, help establish nesting territory and attract a mate. Calls, used year round, communicate with a mate and other birds in a flock.

For example, Black-capped Chickadees use the “chick-a-dee-dee-dee” call to tell other flock members that a predator is near. It’s similar to how we might shout, “watch out!” if we see a car careening toward the sidewalk. On the other hand, the chickadee’s song is a soft “fee bee” or “fee bee-bee” distinctly different from their call.

Even if you’ve noticed that sometimes Black-capped Chickadees add extra “dees” to the end of their calls, you may not realize that these calls represent one of the most sophisticated warning systems in the avian world.

Christopher Templeton, a biology doctoral student at the University of Washington who has studied these birds’ calls, recently cracked the chickadee code. He found that the number of “dees” at the end of the call corresponds to the size and potential threat of a predator.

Through his research Templeton learned that a relatively lesser threat such as a slow-to-maneuver Great Horned Owl garnered only two “dee” notes. But a far greater threat, a small, agile Northern Pygmy Owl warranted an emphatic five “dees.”

To discover this, Templeton hid speakers in trees and played the sounds of potential predators. Then he watched and recorded the calls and reactions of the chickadees.

During the non-breeding season chickadees often hang out with other birds in mixed species flocks. Templeton and a colleague, Erick Greene of the University of Montana, wondered if the warning calls of chickadees in any way communicated information to other birds in these flocks. They wanted to know if birds gained any advantage by eavesdropping on flock mates of different species.

Templeton and Greene focused on the small, alert Red-breasted Nuthatch, a native species that also visits our seed feeders. They found that this common flocking groupie is a particularly astute eavesdropper who pays special attention to the chickadees’ calls. At different times the researchers played two-dee chickadee calls and five-dee chickadee calls and watched the nuthatches’ reactions.

The two-dee calls produced only lackluster responses. The nuthatches responded more vigorously to the five-dee alarm call. They were roughly twice as likely to mob together. Also, they flicked their wings in apparent agitation and sounded their own alarm calls.

As I reflect on this research I’m struck by the cooperation among different bird species. Perhaps down the road we’ll learn of a benefit to the chickadees for flocking with the nuthatches. Could it be as simple as the fact that there is safety in numbers? Or perhaps there is a reciprocal benefit, which we humans have yet to uncover.

Frances Wood can be reached at wood@whidbey.com.