March Speaker Program

Bluebird Eggs

March 23, 2021

Time: 7:00 pm (Tuesday)


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Name of presenter: Scott Johnson

Scott Johnson

Scott Johnson

Scott Johnson is Canadian-born but immigrated with his parents to the Twin Cities of Minnesota at a young age. At age 13, he became an avid birder after delighting in seeing the different birds that came to a rickety bird feeder he built. He obtained a B.A. from St. Olaf College and later a Master’s in Zoology at Northern Arizona University in 1984. His thesis research at NAU, done under Dr. Russ Balda, examined the function of song in what was then called the “Plain Titmouse.” Romance then took him to the foothills of the Bighorn Mountains in Wyoming. He eventually completed a Ph.D. at the University of Calgary and became Professor of Ornithology and Animal Behavior at Towson University in Baltimore, but always returned to Wyoming each spring to do bird research. His work has focused on the reproductive biology and behavior of songbirds. For two decades he studied House Wrens before turning his attention to the Mountain Bluebird. He is now retired and living near Sedona where he continues various ornithological pursuits.

Title of program: Why Mountain bluebirds lay the number of eggs they do

Mt Bluebird

Mt Bluebird

NestWhy birds lay the number of eggs they do is one of the most long-standing and debated questions in ornithology. The normal differs, of course, between species, e.g., hummers typically lay 2 eggs, robins and shorebirds lay 4 eggs, while chickadees lay 8 eggs or more. Mountain Bluebird females usually lay 6 eggs. Clutches of 7 eggs occur, but they are very rare. The question arises then:  Why do females almost always stop at 6 eggs?  If they are capable of laying 7 eggs, why not lay 7 and thus produce more offspring?  Scott will describe a field experiment that he and his students did trying to answer this question. They tested a hypothesis that, while quite logical, has received strikingly little attention from ornithologists: “Females birds lay only as many eggs as they can effectively incubate.” Do females only lay 6 eggs because it is too difficult to incubate 7 eggs?  Before describing the experiment and its results, Scott will give an overview of the biology and behavior of the Mountain Bluebird in the high country of Wyoming.