In total, 11,333 fall migrant monarch butterflies were captured, measured, tagged, and released in southern Pennsylvania over an 18-yr period from 1992 to 2009, excluding 1996 and 2004. Fifty-six (0.494%) were recovered at the Mexican overwintering sites. Hind wing tags had a much higher recovery rate (1.13%) than forewing tags (0.138%). When compared with published recovery rates east of the Appalachians using the same tag type, Pennsylvania was higher than all coastal sites but similar to that of inland Virginia, indicating that inland migrants are more successful. Six U.S. recoveries indicate that monarchs experience considerable eastward wind displacement after leaving the tagging sites. The wild monarchs were divided into three groups for analysis: early (20 Aug–9 Sep), middle (10 Sep–1 Oct), and late (2 Oct–20 Oct) to determine temporal trends. The average forewing length decreased over time, while the percentage of female migrants increased. These trends were not seen in a comparison set of raised monarchs originating from the same general area. As over half the Mexican recoveries came from storm-killed fall 2003 migrants, recoveries were analyzed with and without 2003, and for 2003 alone. More early than middle migrants and no late migrants were recovered. Female migrants were more likely to be recovered from 2003 and overall, but not when 2003 was excluded. The recovery data suggest that males are less likely to make it to Mexico and suffer higher mortality once there during normal overwintering seasons. It also suggests that while early migration is beneficial to both genders, it is even more beneficial for females.
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