Eastern monarch population trends (spring):

  • Highlighted subregion: South. This is where most spring breeding occurs for eastern populations
  • Season: Spring (3/15-5/16). 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. abundance IndexProgramsSpring South (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.