Wed December 22, 2010
Earth Notes - Junco Dads
Flagstaff, AZ – Earth Notes: Junco Dads
In winter it's hard to miss the dark-eyed junco across much of the Colorado Plateau, and beyond. According to the Cornell Laboratory of Ornithology, this widespread, sparrow-sized bird is the most common backyard feeder bird in North America.
You often see them in small flocks: gray-headed birds strutting on the ground or flitting into bushes, flashing their white-edged tails.
They may look alike to our eyes, but behind the scenes juncos experience social pressures at least as intense as those at a high school mixer.
Ecological researchers at Indiana University recently discovered that male juncos with particularly high levels of testosterone sing the sweetest songs, and sport more white on their tails. That makes them sought-after mates, and they do indeed produce more offspring than their plainer cousins.
But these flashy, sweet-talking hunks don't make ideal partners. The study showed that these males are so busy singing and showing off that they're negligent fathers; they don't devote their time to gathering food for their young. Not only that, these testosterone-charged studs are uncautious about predators. They tend to die young and suffer high levels of stress.
As the researchers note, male juncos have to make a tough choice: either maximize the time spent trying to attract mates, or maximize parenting time to give their offspring a better shot. There's no way to do both.
In case you're wondering, it turns out that ordinary-looking male juncos make great fathers. Chalk one up for the regular