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?