Where have all the birds gone from the Ohio and Mississippi river valleys?

I saw only one large white bird flying over the river during this entire trip.

Nearly 3 billion birds have vanished across North America since 1970, and the Ohio and Mississippi river valleys have suffered massive declines due to severe habitat loss and environmental changes.

While millions of migratory birds still travel the Mississippi Flyway during seasonal surges, their overall numbers are a fraction of what they used to be because the landscapes sustaining them have been drastically altered.