{
 "license": "https://creativecommons.org/licenses/by/4.0/",
 "attribution": "Milkweed USA (https://milkweedusa.com), CC BY 4.0",
 "note": "Both are indices rather than censuses. They measure the overwintering generation only and cannot be added together.",
 "generated": "2026-08-31",
 "name": "Monarch butterfly population counts",
 "description": "The two long-running monarch overwintering counts, eastern and western.",
 "eastern": {
  "name": "WWF Mexico, CONANP and the Monarch Fund annual overwintering survey",
  "url": "https://www.wwf.org.mx/",
  "unit": "hectares of occupied forest",
  "method": "Area of oyamel fir occupied by overwintering clusters, surveyed each December.",
  "note": "Year is the year the winter began: 1996 means the winter of 1996 to 1997.",
  "data": [
   {
    "year": 1993,
    "hectares": 6.23
   },
   {
    "year": 1994,
    "hectares": 7.81
   },
   {
    "year": 1995,
    "hectares": 12.61
   },
   {
    "year": 1996,
    "hectares": 18.19
   },
   {
    "year": 1997,
    "hectares": 5.77
   },
   {
    "year": 1998,
    "hectares": 5.56
   },
   {
    "year": 1999,
    "hectares": 9.05
   },
   {
    "year": 2000,
    "hectares": 2.83
   },
   {
    "year": 2001,
    "hectares": 9.35
   },
   {
    "year": 2002,
    "hectares": 7.54
   },
   {
    "year": 2003,
    "hectares": 11.12
   },
   {
    "year": 2004,
    "hectares": 2.19
   },
   {
    "year": 2005,
    "hectares": 5.91
   },
   {
    "year": 2006,
    "hectares": 6.87
   },
   {
    "year": 2007,
    "hectares": 4.61
   },
   {
    "year": 2008,
    "hectares": 5.06
   },
   {
    "year": 2009,
    "hectares": 1.92
   },
   {
    "year": 2010,
    "hectares": 4.02
   },
   {
    "year": 2011,
    "hectares": 2.89
   },
   {
    "year": 2012,
    "hectares": 1.19
   },
   {
    "year": 2013,
    "hectares": 0.67
   },
   {
    "year": 2014,
    "hectares": 1.13
   },
   {
    "year": 2015,
    "hectares": 4.01
   },
   {
    "year": 2016,
    "hectares": 2.91
   },
   {
    "year": 2017,
    "hectares": 2.48
   },
   {
    "year": 2018,
    "hectares": 6.05
   },
   {
    "year": 2019,
    "hectares": 2.83
   },
   {
    "year": 2020,
    "hectares": 2.1
   },
   {
    "year": 2021,
    "hectares": 2.84
   },
   {
    "year": 2022,
    "hectares": 2.21
   },
   {
    "year": 2023,
    "hectares": 0.9
   },
   {
    "year": 2024,
    "hectares": 1.79
   }
  ]
 },
 "western": {
  "name": "Xerces Society Western Monarch Count",
  "url": "https://westernmonarchcount.org/",
  "unit": "butterflies counted",
  "method": "Volunteer counts at California overwintering groves over roughly three weeks around Thanksgiving.",
  "data": [
   {
    "year": 1997,
    "butterflies": 1235490
   },
   {
    "year": 1998,
    "butterflies": 564349
   },
   {
    "year": 1999,
    "butterflies": 267574
   },
   {
    "year": 2000,
    "butterflies": 394781
   },
   {
    "year": 2001,
    "butterflies": 209570
   },
   {
    "year": 2002,
    "butterflies": 99353
   },
   {
    "year": 2003,
    "butterflies": 209820
   },
   {
    "year": 2004,
    "butterflies": 205085
   },
   {
    "year": 2005,
    "butterflies": 221058
   },
   {
    "year": 2006,
    "butterflies": 86437
   },
   {
    "year": 2007,
    "butterflies": 86932
   },
   {
    "year": 2008,
    "butterflies": 130317
   },
   {
    "year": 2009,
    "butterflies": 58468
   },
   {
    "year": 2010,
    "butterflies": 143204
   },
   {
    "year": 2011,
    "butterflies": 92798
   },
   {
    "year": 2012,
    "butterflies": 144812
   },
   {
    "year": 2013,
    "butterflies": 211275
   },
   {
    "year": 2014,
    "butterflies": 234731
   },
   {
    "year": 2015,
    "butterflies": 292888
   },
   {
    "year": 2016,
    "butterflies": 298464
   },
   {
    "year": 2017,
    "butterflies": 192668
   },
   {
    "year": 2018,
    "butterflies": 27721
   },
   {
    "year": 2019,
    "butterflies": 29418
   },
   {
    "year": 2020,
    "butterflies": 1914
   },
   {
    "year": 2021,
    "butterflies": 247237
   },
   {
    "year": 2022,
    "butterflies": 335479
   },
   {
    "year": 2023,
    "butterflies": 233394
   },
   {
    "year": 2024,
    "butterflies": 9119
   }
  ]
 }
}