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Monarch Butterflies in the Western United States
Ashley Spratt & Joanna GilkesonUSFWS Pacific Southwest Region -
January 4, 2017
WMTC Since 1997• Annual monitoring • Volunteer based• 400+ sites known
(Additional 70 anecdotal sites)
• Most Western population data based on WMTC counts
• 1/3 of sites have not been monitored in past 5 years
• Many inconsistently monitored
• Records back to 1970
Western Monarch Thanksgiving Counts
Western overwintering declines = ~74%
Source: The Xerces Society’s Western Monarch Thanksgiving Count
What we know
Threats in the West• Herbicides & Insecticides
(neonicitinoids)• Tropical milkweed & OE parasite • Year-round breeding• Climate change & drought• Various management of
overwintering groves across public/private lands
• Tree loss & development of overwintering sites Monarch on tropical
milkweed courtesy of Vicki DeLoach/CC.
California’s Central Valley
Source: USGS Pesticide National Synthesis Project
We need more informationLess is known about western population• Milkweed probably not limiting factor across all of
west• Amount of interchange between east & western
monarchs• Specific habitat requirements at overwintering
sites• Movement of individuals between overwintering
sites • Natal origin of overwintering western monarchs • Management &control of
invasive Eucalyptus trees • Tropical milkweed & planting
milkweed near overwintering grounds
Tagged Monarch Recoveries
Migration of Western monarchs
Map Courtesy of Gail Morris, Southwest Monarch Study
Western monarchs overwinter both in California & Mexico, although the relative proportions are unknown
Same species, different messages
Breeding Season & Milkweed• Historic records show milkweed did not grow by
coast• Milkweed probably not limiting factor across all of
west (Central Valley is exception)• Native milkweed is not widely available in
Western nurseries• Plumeria mimicks milkweed (maybe)
Messages• Do not plant milkweed within
10-15 miles of overwintering grounds• Do not plant tropical milkweed,
if you do, cut it back in the winter Plumeria courtesy of Vee Satayamas/CC.
To inform planting milkweed in WestUSFWS/Xerces Western Monarch & Milkweed Habitat Suitability
Assessment
Same species, different messages
Overwintering• Most vulnerable stage of lifecycle • Sites dispersed from Mendocino County to Baja
California, Mexico (620 miles), • Small clusters reported inland in Kern/Inyo
Counties• More than half priority sites on public lands, some
on private lands including golf courses & oil or natural gas facilities
• Use of eucalyptus trees, monterey cypress, monterey pines & others
• Less vulnerable than eastern to severeweather; degradation of one site hashuge impact on population
• Movement throughout the winter
Western monarch communications
Current Efforts• Western monarch website • Developing western messaging (ongoing) • Storytelling in english and spanish• Promoting local citizen science efforts
(Southwest Monarch Study, etc.)• Dia de los Muertos event – October • Schoolyard habitats
Service programs & monarchsPartners for Fish and Wildlife - private land restoration, enhancement & milkweed surveysCoastal Program - overwintering site research & management plans, monarch tagging & OE samplingSchoolyard Habitat - education &school involvementRefuges - public outreach, pollinator gardens, milkweed surveys & enhancementES Field Offices - public outreach, pollinator gardens & Department of Transportation and Energy partnerships
Photo by: Keenan Adams, USFWS
Questions?