I added monthly statistics to the National Transit Database web site which show the monthly year-over-year gainers and losers in ridership for each month. Some transit systems are rather small, so big swings will be seen for some of those smaller systems.
However, there are some larger systems that are seeing large gains and losses. For instance, Albuquerque, NM saw a 54% ridership increase in its bus service. Meanwhile, Tallahassee, FL saw a 33% drop in bus ridership in April.
Feel free to explore the site and email with suggested additions.