Tomorrow's For the Birds
One of my favorite bird songs is produced by the lovely
little Field Sparrow. Field Sparrows have soft rusty and gray plumage with an
eye-ring that gives them an anemic appearance, and a pinkish-orange bill that
makes me think of a pre-schooler trying on lipstick.
I find Field Sparrows adorable, but am utterly charmed by
their song. Their slurring notes are incomparably sweet, staying on the same
pitch while picking up speed, giving them the rhythm of a drumming Ruffed
grouse. When I took college ornithology, I did a study of Savannah Sparrows
that nested in a large brushy field behind the house I was living in. I could
work out their home territory by playing their calls on a tape recorder and
mapping the perches on which they responded. The paper I wrote about the
experiment was focused on Savannah Sparrows, but the bird that caught my
attention was the Field Sparrow. Savannah Sparrows responded only when I played
recordings of the songs of their own species while I stood within their territories,
but wherever I stood and whatever species I played, nearby Field Sparrows approached
and sang every time. Intriguingly, most studies seem to find that Field
Sparrows aren’t particularly aggressive compared to most songbirds, and they
don’t defend a territory against other species, but I found them consistently
responding much more than other species to recorded songs. It’s possible that
they’re simply more curious about everything that happens on or near their
territories than the other species in the area.
Those of us in northernmost Wisconsin and Minnesota are at
the northern border of or slightly out of the range of Field Sparrows, but just
south of us they are a common species of brushy pastures and second growth
scrub. Common as they are, they do tend to avoid developed areas much more than
Song and Savannah Sparrows do, and so usually appear at feeders only in rural
areas.
Their numbers are strong, but overall the species is declining for a
variety of reasons, including increasingly intensive farming practices, early
mowing of pastures, and development. Increasing numbers of White-tailed Deer
and Wild Turkeys may also be taking a toll--both game species feed on eggs and
chicks of low-to-the-ground nests more than most people realize.
As with many birds, Field Sparrow diets change seasonally.
In winter, seeds comprise more than 90 percent of their daily intake, but by
summer more than 50 percent of their diet is made up of insects, spiders, and
other small arthropods.
When Field Sparrow numbers are strong, they sing more often,
and females more often mate occasionally with neighboring males such that the
offspring in a nest may have more than one father. In one Pennsylvania study, this kind of DNA fingerprinting
indicated that in 1990, fully 20 percent of all nests included at least one
chick fathered by a male other than the social mate. By 2000–2002, when the
population size was significantly smaller, the number of young with different
fathers had dropped to zero.
Field Sparrows are surprisingly nurturing and peaceable
while nesting. When one pair nested less than 2 feet from a pair of Eastern
Towhees, both species fed the young at both nests. In another case, a pair of
Field Sparrows and a pair of Common Yellowthroats actually shared the same nest,
both incubating full clutches at the same time. I treasured Field Sparrows long
before I knew that. It’s yet another case in which the more I learn about a
bird, the more wonderful it turns out to be.