De-lightful Birdsong
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It's Spring, and no doubt you've heard the birds engaging in one of their favorite pasttimes-singing . Hi, I'm Dave Thurlow and this is the Weather Notebook. It turns out, there are biological reasons for this seasonal rise in avian song. Correspondent Jeff Rice files this report.

Birdsong is as much a part of spring as flowers and romance. The warmer weather with more food signals to birds that it's a good time to start a family. So the males start warbling their love calls in earnest.

But there's another reason that the air is filled with song and it has to do with light and chemicals. In the spring, the changing angle of the earth's rotation around the sun makes the days gradually get longer, which increases the amount of daylight or "photoperiod." Biologist Stephen Hopp of the University of Arizona says more light affects key chemicals in birds.

The day-length increases the testosterone in males which changes the structure of his brain which increases the amount of singing.

Hopp studies bird vocalization and is co-editor of the book "Animal Acoustic Communication. Unlike humans, says Hopp, most birds prefer a bright sunny day to a candle lit rendevouz.

I mean on a physiological level it sounds sort of ABC and this is why they sing. It doesn't sound very romantic to put it that way. But we know that's the case. I guess you could say it's the bird equivalent of spring fever.

Photoperiod is only part of the story. In the summer, when there is even more daylight, factors like hot weather and the end of the mating season will reduce how much our feathered friends sing. During those times, birds are more likely to vocalize in the cool of the morning or evening, or after a rain.

Thanks go today to correspondent Jeff Rice of Idaho. The Weather Notebook is supported by the National Science Foundation and Subaru.