monarch-esa-petition-final_61585

eastern North American butterflies. Forewings of monarchs from non-migratory monarch
populations in South Florida are both smaller and rounder than forewings of migratory
populations of D. p. plexippus (Dockx 2012).
RANGE
For D. p. plexippus in North America, the geographical range encompasses breeding areas,
migration routes including staging areas, and winter roosts. During the spring and summer
breeding season, D. p. plexippus disperses throughout the United States and southern Canada
when successive generations migrate and expand north with the availability of suitable
milkweeds as summer progresses. During winter, butterflies that primarily originate from east of
the Rockies converge on specific locations in Mexico, contracting from a summer range of about
100 million hectares to winter roosts that total 20 hectares at most (Wassenaar and Hobson 1998,
Oberhauser and Solensky 2004, p. 79, Commission for Environmental Cooperation 2008).
Monarchs that breed along the east coast migrate to Florida (Knight and Brower 2009), where
some fly west along the coast of the Gulf of Mexico and continue to Mexico, or apparently
integrate into stable populations in Florida. A few continue migrating to Cuba and other islands
in the Caribbean (Dockx 2012). Monarchs from west of the Rockies primarily fly to a series of
roosting sites centered along coastal areas of south-central California (Jepsen and Black in
press), although some migrate to the Mexican roosts used by eastern monarchs (Brower and Pyle
2004, Lyons et al. 2012).
Some monarchs have established small non-migratory populations in southern Florida and areas
along the Gulf of Mexico where they reside year-round. Some monarchs that migrate to Florida
to overwinter apparently integrate into the stationary populations (Knight and Brower 2009), and
some continue to Cuba and integrate into populations of a monarch subspecies found in the
Caribbean (D. p. megalippe) (Dockx 2002, Dockx 2007, 2012). Since they do not migrate, some
researchers classify monarchs in southern Florida as D. p. megalippe (Smith et al. 2005), but
others consider them to be D. p. plexippus (Pelham 2008). The establishment of stationary
populations in Florida and other southern areas may be facilitated by the spread of nonnative
heat-tolerant milkweeds in the southeastern states (Harvey et al. 2009).
In the past two centuries, D. p. plexippus has established small non-migratory populations in
non-native habitats outside of continental North America (see Appendix A of this petition).
Monarchs are thought to have moved both east and west of North America, and between various
islands via favorable winds and storms, by hitchhiking on boats, and by intentional human
introduction (Clarke and Zalucki 2004, Zalucki et al. 2004). During the mid- to late-1800s,
monarchs spread across the Pacific Ocean to Hawaii, Australia, New Zealand, and many other
islands (Zalucki and Clarke 2004). During this same time period, monarchs also moved across
the Atlantic, colonizing islands including the Azores and Canary Islands, and coastal areas of
Spain (Haeger et al. 2011). Various lines of evidence point to more than one introduction event
in the Pacific, with populations in Hawaii and Australia likely forming independently (Lyons et
al. 2012, Shephard et al. 2002), and other Pacific islands being colonized by radiation from
original areas (Zalucki et al. 2004). Introduction and spread in the Atlantic and Spain have not
been as well studied.
Monarch ESA Petition 18