The songs of the chestnut-sided warbler holds clues to its behavior.

It's 4:00 AM in the Berkshire Hills of western Massachusetts. Alan and U. Mass biologist Bruce Byers are listening to the "dawn chorus," the cacophony of birdsong that erupts most spring mornings in the Savoy State Forest. In "Songs of Love and Betrayal," Alan and Byers attempt to sort out the soap opera-like mating habits of the chestnut-sided warbler.

Only the male chestnut-sided warbler sings, and only during mating season, so the singing seems to be associated with successfully defending a territory and attracting a mate. To check his hypothesis, Byers captures and bands the individuals within one territory. The colored leg bands will help him keep track of which bird is doing what.

The first bird Byers and Alan catch is male, and Byers assumes it's the territory's resident male. But as they release the newly-banded bird, everyone hears a warbler's "pleased-pleased-pleased to MEET-ya" mating call coming from another male a few feet away. Since only resident males sing the mating song, Byers begins to suspect the bird he's just banded was up to no good - hoping to mate with a female he won't have to provide for.

Biologist, Bruce Byers, picks out the warblers'song from the morning cacophony.

In an attempt to catch and band the real resident male, Byers plays a recording of a female warbler. But this time, a female shows up, probably to defend her own right to the resident male. As Alan comments, she's holding her mate to a kind of double standard, enforcing his fidelity while carrying on with intruding males. When Byers administers paternity tests to the baby warblers that spring, about half the chicks turned out NOT to be fathered by the male that provides for them.

To human ears, it sounds as though the males all sing the same song. So what's a female chestnut-sided warbler looking for in a mate and how does she choose? Byers takes a sonogram - a kind of a picture of the sound - of males' mating calls and compares them. Consistent songs with few variations seem to be the key to a male's attractiveness - and the key to the female chestnut sided warbler's heart, if not her loyalty.

For more on this topic, see the web feature:
The Mating Game