Excerpts from Jim Conrad's
from the April 14, 2008 Newsletter written in the community of 28 de Junio, in the Central Valley 8 kms east of
Pujiltic, Chiapas, MÉXICO
about 800 meters in elevation, ± LAT. 16° 18'N, LONG. -92° 28'
Usually when I pass a certain cornfield on my way to the reserve I hear the slurred, buzzy, slightly metallic TZSSIIU song of a male Blue-black Grassquit, VOLATINIA JACARINA SPLENDENS. Most of the time he's accompanied by a small flock of females and immatures. With their size, form and short, thick beaks, male Blue-black Grassquits look like Indigo Buntings with their blueness darkened to the point of being almost black. Brownish, streak-breasted females are reminiscent of Song Sparrows.
Since the species specializes in weedy fields and second growth, of which tropical America has a lot, the species is fairly common and I wouldn't bother telling you about them except for the funny thing the male does when he sings:
Each time he TZSSIIUs, he jumps. It's more like a brief flight upward for a foot or two, then instantly he returns to his perch, and when he calls again a few seconds later he jumps once more. How on Earth could such a behavior have evolved and how does it serve the species?
Maybe the jumps help females better judge how vigorous the male is. That makes sense now that they're still in small flocks preceding the rainy-season nesting period, but I've seen them doing it when supposedly they were defending territories, thus already had their mates.
Jumping certainly draws attention to the males making them more vulnerable to predation, but maybe that's exactly what Mama Nature wants. In this species with abundant habitat and easy-to-find food (small weed seeds), once nests are established maybe part of the relatively expendable male's "job" is to remove his genes from the species gene pool if he's not alert or fast enough to dodge incoming predators. It wouldn't be the first time Nature has evolved a species producing individuals with self-destructive behavior.
If someone else has another idea how this behavior might serve the species, maybe you can post your theory at our Google Backyard Nature forum at http://groups.google.com/group/backyard-nature/.