3 years ago



Monarchs are thought to

Monarchs are thought to have moved between islands via favorable winds and storms, by hitchhiking on boats, and sometimes by intentional human introduction (Clarke and Zalucki 2004, Zalucki and Clarke 2004, p. 115). None of the non-North American monarch populations migrate as a regular part of their lifecycle, although they may move in response to habitat changes. There are reports and studies of migratory behavior of monarchs in Australia and New Zealand during winter from colder to warmer areas (Ramsay 1964, James 1993). These movements, however, are not comparable to the yearly two-way migrations in North America. Establishing a population on the “next island” in this way is only possible if non-native milkweed host plants are already present when monarchs arrive. Although widespread, to our knowledge the distribution of these milkweeds, and thus the potential for resident monarch populations, is incomplete. There are surveys of milkweeds on some but not all islands in the Pacific and Atlantic, so the proportion of islands inhabited by milkweeds and that are thus potentially suitable for monarchs is unknown. There are no published estimates of the total number of monarchs outside of North America as there have not been any comprehensive surveys or censuses. Nor are there regular studies of particular populations specifically to determine their relative status and threats. However, some information about status and threats can be gleaned from more general studies of monarch biology in various non-North American locations, both west and east of the continent. Polynesia Polynesia consists of more than a thousand islands scattered over the central and southern Pacific Ocean. Monarchs were first described in this region in the Hawaiian Islands in 1840’s, and monarchs were reported from New Zealand then, as well. Genetic studies support the contention that these were separate introductions (Pierce et al. 2014). Monarchs are widely reported throughout Polynesia (e.g. Clarke and Zalucki 2004, Appendix), including Tonga, Vanuatu, the Marquesas, Samoa, and Tahiti, although current status on particular islands is not generally known. Hawaii There are resident populations of D. p. plexippus on all the major Hawaiian islands, and they use a variety of introduced host plants, mainly Asclepias curassavica, Gomphocarpus physocarpa, Calotropis procera, and C. gigantea. Both Calotropis species are planted widely around houses and in gardens. In fact, flowers of C. gigantea are prized and grown for leis, and were reputed to be the favorite of Queen Lili’uokalani (b. 1838 – d. 1917) (Cook 2013). All are naturalized. Monarchs were reported in Hawaii by the mid-1800’s: “…A. curassavica is believed to have been introduced to Hawaii in the period 1845–1850 (Wagner et al. 1990), with monarchs recorded there somewhere between 1841 and 1852, but after the milkweed (Scudder 1875)” (Zalucki and Clarke 2004, p. 114). Whether they arrived on their own or hitchhiked on a ship is not known. Recent genetic studies using microsatellite markers show little genetic differentiation between monarchs on the four Hawaiian islands sampled, indicating that they form one admixed population (Pierce et al. 2014). The Hawaiian monarch population has fewer alleles at the loci studied than the North American population (Pierce et al. 2014), consistent with being founded Monarch ESA Petition 150

y one or a few butterflies and then being separated from the main population, and in line with genetic diversity studies using allozymes (Shepard et al. 2002). There are no estimates of numbers of monarchs in Hawaii. Numbers fluctuate, as discussed above, based on milkweed status. Threats to introduced milkweeds and monarchs in Hawaii have not been studied. New Zealand Monarchs were first reported in New Zealand in the 1840’s (Ramsay 1964). There are no native milkweeds in New Zealand (Elliot et al. 2009, p. 603). Hosts for monarchs that have been introduced to New Zealand are Gomphocarpus fruticosis, G. physocarpus, Asclepias curassavica, and A. incarnata. These milkweeds are specifically cultivated to host monarchs because New Zealanders are so fond of these butterflies (Wise 1980, p. 157; Monarch Butterfly NZ Trust 2009, as cited in Elliot et al. 2009): “Although the monarch butterfly D. plexippus, is exotic in New Zealand, it is an iconic species” (Elliot et al. 2009, p. 606). Although it appears that most monarchs are raised on garden plants, G. fruticosus is listed as “naturalized” in New Zealand, confined to waste places and old gardens around habitations, see: 6f3d9d5fc4cc&fileName=Flora%204.xml There are no estimates of the monarch population size, their status, or threats. Micronesia Micronesia is comprised of thousands of small islands in the western Pacific Ocean, such as the Caroline Islands, including Palau, Gilbert Islands, Mariana Islands, Marshal Islands, Nauru, and Wake Island. Monarchs are widespread, occurring on all major island or island groups with the possible exception of Kosrae (Schreiner and Nafus 1997). Monarchs were first reported in 1857, introduced from Hawaii via a shipment that contained milkweed seed (likely A. curassavica) to Pohnpei (Kilonia = Ponape), Caroline Islands (Scudder 1875). The main host now is Calotropis gigantea. There is no information on status or threats. In Guam, monarchs seem to have reduced their original host plant population, but the effect on monarchs themselves is not noted. According to Shreiner and Nafus (1997, p. 34 – 35): On Pacific islands this butterfly shows up soon after host plants arrive. In 1936, Swezey noted that the weed A. curassavica was very abundant on Guam, forming dense stands almost acres in extent, and the butterfly was also very abundant. Possibly the butterflies provided some control of the weed, as it now never forms dense stands. Monarchs have recently been described in Nauru (Buden and Tennent 2008) using Calotropis gigantia, where they are commonly found near host plants along roadsides and yards in the coastal belt. There are seasonal fluctuations in numbers of monarchs, but status and threats are unknown. Monarch ESA Petition 151

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