Bobolinks portrait by Major Allan Brooks
Most of our grassland birds are in serious trouble. The populations of field, grasshopper and savannah sparrows have declined precipitously and Henslow's sparrows are no longer to be found. Meanwhile, that lovely whistle of the meadowlark, teyou toowee, and their flight chatter, both formerly heard from open fields are now only rare treats.
Few people realize that grasslands need conservation as well as woodlands. Unless they are cared for, succession takes over. It takes only a few years for the meadow to disappear, replaced first by bushes, then by trees. To retain a meadow, the land must be plowed every year or two.
Of course, grain crops like wheat or oats are also grasslands, but harvesting schedules, especially for winter wheat can destroy nests. We need wild meadows.
Despite these problems, however, one species, the bobolink, is doing quite well.
I joined Paul Kielich for a pleasant walk around Knox Farm State Park a few days ago and we came across at least a dozen bobolinks. Their bubbling spink-spank spink-spank calls, often given in flight, resounded across the fields. Their bobolink or bobolincoln name evidently arises from their song, rather than from some human connection. Aside from the many swallows, bobolinks were the most common birds we found on our hike.
The male bobolink is easily identified. It is our only eastern bird whose back is lighter than its underside. Its base color is solid black: this is the color of its head, breast, belly, tail feathers and even its eyes. Its back, however, is mostly white and buff colored.
This is an anomaly among birds. Almost all birds have lighter breasts than backs. There is an evolutionary value to this dark above-light below coloration. Camouflage is important to birds: it can serve them as a defense against raptors or hunters.
There is a simple experiment that shows the possible value of this normal color pattern. Hold a ping pong ball or golf ball under a lamp. Notice how it is light above and dark below because the bottom is shadowed. Only if you darken the top side does the difference in coloration disappear and the two blend in.
The bobolink breaks that general rule. Its topside exaggerates the color difference making it a very striking bird. Why is this? Your guess is as good as mine.
Female bobolinks (should they be called robertalinks?) fit the normal pattern. They are drab brownish birds - slightly darker above - that look like female house sparrows.
As are most meadow birds, bobolinks are ground nesters. Their nests are woven grass, sometimes with a canopy. They are very difficult to find because the females, rather than flying to perches near the nest, instead drop into the grass some distance away and creep to it through the undergrowth. This is probably one reason their nests are rarely parasitized with cowbird eggs. The bobolinks' own four to seven eggs are cinnamon or gray, usually heavily spotted with brown.
Stomach analyses of bobolinks indicate that their diet when they arrive in the north in early May is almost 90% insects with over the summer months increasing amounts of plant food as those plants mature, a mix of weeds like doc and grain crops. Those results were obtained before winter wheat was widely planted, however, and the proportion of grain probably makes up more of their early summer diet today. In any case, by September when they depart, their diet is 80% grain.
Depart indeed. Bobolinks fly south 6,000 miles to Argentina, Bolivia and Paraguay to spend the winter, some flying as much as 1000 miles in one night.
Their southern excursion is not altogether pleasant. In Jamaica they are known as butterbirds because of the fat they gained for migration. There they are often harvested for food. And when they get to their southern destination, where they are called ricebirds, they are shot as crop destroyers.
Bobolinks go through two complete molts each year, the males and females similar when they are in South America. When the males molt back into their bright color, new feather ends cover these colors completely. Only when that feather rust wears off do they become the handsome birds we know.-- Gerry Rising