In the western United States, the population of migratory monarch butterflies is on the brink of collapse, having dropped from several million butterflies in the 1980’s to ~2000 butterflies in the winter of 2020-21.  At the same time, a resident (non-migratory) monarch butterfly population in urban gardens has been growing in abundance.  The new resident population is not sufficient to make up for the loss of the migratory population; there are still orders of magnitude fewer butterflies now than in the recent past.  The resident population also probably lacks the demographic capacity to expand its range inland during summer months.  Nonetheless, the resident population may have the capacity to persist.  This sudden change emphasizes the extent to which environmental change can have unexpected consequences, and how quickly these changes can happen.  We hope it will provoke discussion about how we define resilience and viability in changing environments.

WMMOD_immaturesEL

For methods, see Supplemental analysis 1:  Changes in abundance of coastal monarch butterflies through time.  Data were downloaded from the Western Monarch and Milkweed Occurrence Database (https://www.monarchmilkweedmapper.org/) on 4 February 2021. MonarchObservationID is unique identifier from the Western Monarch and Milkweed Occurrence Database (WMMOD; note that columns 1-12 are all directly from WMMD). Column 13, region, identifies whether observations are north (TRUE) or south (FALSE) of 35 degrees latitude.

BerkeleySurveys 

For methods, see Supplemental analysis 2: Estimating the population size of urban resident monarch butterflies. route_length_m is length of survey route in meters. adults is number of monarch adults sighted.  larvae is number of monarch larvae sighted.  pupae is number of monarch larvae sighted. TMW_stems is number of tropical milkweed (Asclepias currasavica) stems counted. xmin and ymin are the minimum longitude and latitude of the survey, in decimal degrees.  xmax and ymax are the maximum longitude and latitude of the survey, in decimal degrees.  rain is whether or not there was rain during the surveys; "no" means no rain during the survey; "yes" means rain during the survey; only days with no rain were used in estimates of adult monarch density. surveyors is number of people participating in survey; when surveyors = 1 only one side of the street was surveyed for plants and larvae; when surveyors = 2, both sides of the street were surveyed.

CaptureRecapture

For methods, see Supplemental analysis 4: Rates of increase of healthy and diseased monarch butterflies.  These are capture-recapture data, formatted for use in the RMark package in R. These data were combined with field data on egg-laying and published parameters to calculate per-generation growth rates. ch is capture histories of individual butterflies (0 = not captured; 1 = captured).  sex is M for Male, F for Female.  OE is infection with the protozoan parasite Ophryocystis elektroshcirriza (yes = heavily infected; no = not heavily infected). int is time interval between surveys (this column is not associated with values in the same row for other variables, as is typical in RMark files).

DailyEggsEL

For methods, see Supplemental analysis 4: Rates of increase of healthy and diseased monarch butterflies. These data are for healthy monarch butterflies in the field.  They were combined with mark-recapture data and published parameters to calculate per-generation growth rates. Daily monarch butterfly egg-laying rates, from a field study by Norah Warchola at Camp Dodge IA in summer 2018. Butterfly.Number is unique numerical identifier for each individual.  Mark is unique color mark for each individual. Date.In and Time.In are date and time that adult female was placed in cage. Date.Out and Time.Out are data and time that adult female was removed from cage. Cage is cage number. Eggs is number of eggs laid during this time period.