During the long days of mid-summer in East Central Minnesota, the ditches of our county roads are inhabited by an assemblage of notable singers, often hidden but distinctly heard. Sedge Wrens, Common Yellowthroats, Dickcissels, Savannah Sparrows all sing from the grasses or shrubs lining the road, but the singer that delights me most is the Bobolink, whose bubbly musical song arises from grasses and hayfields on summer mornings. To listen, click here: https://www.youtube.com/watch?v=8TXIrXiyW6o
Bobolinks are among the last of the migrants to arrive on their breeding grounds in Minnesota. They come from a distance—the Pampas of Argentina, Paraguay and Boliva, a trip of over 6,000 miles one-way. The migration is a feat in another way—they fly non-stop over the Gulf of Mexico, then continue farther south to the grasslands offering seeds, which comprised the bulk of their diet. Biologists estimate that some birds living up to 10 years will fly a distance of 5 times the circumference of the earth on their annual migrations.
Like many small songbirds, bobolinks are night migrators. They are known to use the stars as a compass to orient; and recently, researchers have discovered that a migrating flock also uses the earth’s magnetic field. The birds detect this through iron oxides compounds in their nasal cavities and in tissue around the olfactory bulb and nerve. Different wavelengths of light also appear to play a role.
On their breeding grounds here in Minnesota, male bobolinks look like no other bird, sporting a light straw-colored back of head and light-colored back, with a black face and breast. The striking plumage makes a territorial bird stand out. Females look much different, as do juveniles, being buffy and dull-colored with brown stripes on the head. I will admit to spending quite a bit of time in a gravel pit one day, after 50 years of birding, trying to figure out what the heck those small brown birds were, only to reach an ah-ha moment when I landed on the bobolink page of my field guide.
Relatives of blackbirds, bobolinks are known to be polygynous—one male might have several females as mates with separate nests. Unlike black birds, bobolinks are also known to be polyandrous—that is, one female might mate with several males, and lay a clutch of eggs from different fathers.
Bobolinks nest on the ground in meadows and hayfields. Since June is the time of first cutting for hay, their nests are often casualties of the mower. Twenty-first century haycutting is occurring two weeks earlier than in the 1950s. For this reason, and others, bobolink populations are declining. They have been designated a “species in greatest Conservation Need” by Minnesota’s DNR and are on the Partners in Flight Watch List for 2016. For more information on Minnesota’s bobolinks, see the Breeding Bird Atlas: https://mnbirdatlas.org/species/bobolink/