Eastern monarch population trends (summer):

  • Highlighted subregion: Northcentral. This is where most breeding occurs for eastern summer populations. Northeast is another important breeding zone.
  • Season: Summer (5/17-8/15). Seasons are defined by monarch activity
  • Featured program(s):
    • NABA: ~500 count circles are surveyed throughout North America each year and the number of all butterflies observed are reported. Raw scores are the number of monarchs seen for each party-hour.
    • Illinois-BMN. A Butterfly Monitoring Network where individual volunteers do regular surveys along set transects in the Illinois region. Raw scores are the number of monarchs observed for each hour.
00.250.50.75119931995199719992001200320052007200920112013YearRelative abundance IndexProgramsSummer Northcentral (Illinois-BMN)Summer Northcentral (NABA)Summer Northeast (NABA)

All trend graphs show “relativized” abundance indices.  This means that “raw” scores that measure some index of abundance are transformed so the highest value in the series is equal to 1, and all other values are then relative to the highest value.  This allows scores to be overlaid among programs so that yearly dynamics can be compared.  The “raw” score measured varies and is described separately for each program.  The length of the time series (start and end year) vary depending on how long the programs have run and how much data we have received from each program.