These birds do not nest in trees. Instead, they lay their eggs in the grass, sometimes in small depressions in the soil and sometimes in little pillows of straw. When there were great open fields in the prairies and the farmlands of the Northeast, the birds were fine. But that has changed. First, the large, open natural meadows that would have sustained these birds, particularly along coastal and marshy areas, have been developed.
People like to live near the water.
Second, farmers need to get more out of their land. This pattern, as well as the intensive grazing of pasture, literally destroy the nesting bobolinks as they try to establish a nest. It's not uncommon to see a hayfield the day before cutting, heavy with nesting bobolinks. Finally, and perhaps ironically, the decline in agriculture in the Northeast means that many once-open fields have returned to woodlands. While the reforestation of New England may be good for forest birds, it is just as depressing as a strip mall development to a meadowlark.