Western monarch population trends (spring):

  • Highlighted subregion: Greater California.  This is where most breeding occurs for western populations
  • Season: Spring (3/15-5/16).  Seasons are defined by monarch activity
  • Featured program(s):
    • Shapiro:  11 transects where the presence/absence of all butterfly species is measured bi-weekly.  Raw scores are the probability of seeing a monarch during any one survey.
00.250.50.75119931995199719992001200320052007YearRelative abundance IndexProgramsSpring Greater California (Shapiro)

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.