Curious Nature: The sparrow backstory
Special to the Daily
Vail, CO Colorado
There was a time when I classified birds according to a color scheme: red, blue or LBJ – little brown job. Then I got my first pair of binoculars. Before I knew it, I needed a bird guide and found myself jotting down bird names, dates and locations. I had crossed the line between bird watching and birding. Once that happens, the birdwatcher-turned-birder must take on the sparrows, the most intimidating of the LBJs.
To the novice eye, sparrows all look alike. This is a problem for newly obsessed birders intent on assigning correct names to the beautiful creatures at the ends of their binoculars. Sparrows are only 5 to 7 inches long. Most skulk around on the ground, darting into the grass or bushes before the binoculars are focused. Sparrow identification begins like this: See an LBJ, lock eyes onto the location, raise the binoculars, focus and look for the signature features that make the LBJ a Lincoln’s, grasshopper, vesper, lark, savannah, fox or song sparrow, just to name a few. Remember that all LBJs aren’t sparrows. Some are pine siskins, finches or little thrushes. The ubiquitous house sparrow is, according to real birders, a weaver finch.
In birding, signature features are called field marks. They include such things as eye rings, breast streaks and spots, cheek and eyebrow color (yes, birds have eyebrows) and head stripes. The successful birder notes all of this in a few seconds before the bird exits the binocular frame. Then he whips out the field guide.
What happens next is something Lorenzo Gonzales in his book “Deep Survival” calls “bending the map.” He was referring to the more serious matter of being lost in the wilderness and trying to read into the surrounding landscape a feature that the map shows, thinking, for instance, “that could have been a lake over there and it’s just filled in over time.” The birding equivalent of bending the map? “Well … that spot on the breast could have been bunched-up stripes.”
Persistent birders eventually discover effective identification shortcuts that narrow the possibilities they must consider. Some sparrow species have similar tail shapes, head curves, body widths and neck lengths. Some like brushy ground for nests and feeding and tend to congregate in like-minded flocks. Some are loners who shun attention, while others sing melodic sets of clear notes and trills while perched alone on a tree top. Some switch diet from insects to seeds when spring finally blooms.
Once the birder realizes that LBJs have preferences, curiosity compels another question. Why are there so many different versions of sparrows? That’s the kind of question that prompted Charles Darwin’s theory of evolution after he encountered a dizzying array of finches in the Galapagos Islands.
The original finch family members arriving on the Galapagos Islands became separated from one another long enough to develop traits that helped them survive in the environment in which they landed. Gradually, they became different species of finches, no longer able to mate with finches from the other islands. But the ancient sparrow family that populated the New World faced no such travel barriers. How did those birds separate enough over time and space to become different, nonmating species?
The answer is glaciers. Each time glaciers advanced down the North American landmass, sparrows were funneled into isolated locations where different environmental circumstances selected for different genetic traits. When the weather warmed up and the glaciers retreated, some reunited groups of sparrows were unable to mate and/or produce viable offspring. But they could remain together in a given geographic area because their preferences took advantage of different environmental niches and food supplies. Some of them preferred the edges of woodlands, some the grasslands and some the banks of streams, making it possible for all those LBJs, who still resemble one another enough to frustrate birders, to utilize more resources than they might if the glaciers had never separated them. Nature is all about economy.
Betsy Holter is a medical writer (byline Elizabeth A. Reid, M.D.) and volunteer at Walking Mountains Science Center. She is really a bird watcher, not a full-fledged birder.