Study of birds shows firstborn may not be the last standing

   News bulletin: Despite the cliché to the contrary, the early bird doesn't always get the worm.
 

   At least not if the bird is a Lincoln's sparrow, living high in the San Juan Mountains of Colorado.

    That's what Keith Sockman has found, after studying the diminutive songbirds nesting in subalpine meadows at 10,500 feet on Molas Pass.

    Sockman, 39, a 1986 graduate of Cheyenne Mountain High School, is an assistant professor of biology at the well-regarded University of North Carolina at Chapel Hill. He's just published a paper in the natural science journal PLoS ONE that challenges notions about the benefits of being the firstborn - or in this particular case the firsthatched.

    Over the past three summers, Sockman, accompanied by students, has camped on Molas Pass and studied the nesting patterns of the migratory songbird. Sockman has discovered that contrary to common wisdom held about many species, the first egg laid among Lincoln's sparrows doesn't have the best chance of surviving.

    In fact, Sockman said Wednesday, among the sparrows he has studied, the first laid egg is least likely to hatch.
    Take that, you bullying older brother!

    Sockman said there appears to be several reasons: The first of the three to five eggs laid by Lincoln's sparrows - generally all laid one day apart - sits longer in the cold night temperatures of the San Juans and also is exposed more to warm daytime temperatures, which can cause the growth of harmful bacteria and fungi.

    Also, because the mother sparrow must forage for food, she doesn't spend much time warming that first egg with her body. It isn't until the third or fourth egg that the mother has the time to incubate her eggs.
    By that time, Sockman said, the toll of weather and lack of warmth has taken its toll on the first egg.

    Sockman said it has long been thought that first-laid eggs - because they hatch first - have an advantage among younger, less mature siblings when it comes to competing for limited food.
    Sockman's work challenges that.

    "Most of the studies (looking at hatching order) failed to look at mortality before the hatching occurs," he said. "It turns out the first one laid, when it hatches, does best. But it is the least likely to hatch among all of them.

    "This kind of evens out the value of prospects for the offspring and, in the end, all the eggs stand a relatively even chance," he said. "The female seems to be balancing the odds to maximize the fitness of her offspring."

    Of course, for the poor Lincoln's swallow, surviving to fledge is just the first step. As summer comes to an end, the birds migrate to the southern U.S. or Mexico, and return late the next spring. Sockman said probably only about 10 percent of the young sparrows survive that first year.

    If they do make it, they begin mating that season, and stand a roughly 50 percent chance of surviving each of the coming migration cycles. He thinks the birds generally live about four to six years.

    This summer - yes, Sockman loves returning to Colorado - he and his students will begin to study the implications of hatching order among the sparrows as they become adults: For example, does the limited food supplied by the mother compromise the strength of her last-hatched offspring once they become adults? Are the last-hatched less choosy as adults in selecting a mate because they themselves are weaker or less competitive?
    "It raises interesting questions about the trade-offs during reproduction in many organisms," Sockman said.

CONTACT THE WRITER: 636-0197 or bill.mckeown@gazette.com