Changes in agriculture, such as switching to early-harvest varieties of alfalfa, severely impacted those birds that adapted to nesting in grassy farm fields.
(Changes in agriculture, such as switching to early-harvest varieties of alfalfa; severely impacted; those birds that adapted to nesting in grassy farm fields) (those birds; adapted; to nesting in grassy farm fields)
Changes in agriculture, such as switching to early-harvest varieties of alfalfa those birds
severely impacted adapted
those birds that adapted to nesting in grassy farm fields
to nesting in grassy farm fields