Microclimatic Conditions that Promote Monarch Butterfly Colony Movement While Overwintering in Mexico Alfonso Alonso, Eduardo Rendon, Eneida Montesinos, Lincoln P. Brower Contact: Dr. Alfonso Alonso: [email protected] Background Results Monarch butterflies overwinter in high altitude The overwintering aggregation departed from the forests in Mexico dominated by the Oyamel fir study site when: tree (Abies religiosa). They move to lower 1.Ambient temperature in the shade was <16˚ C (the elevations as the overwintering season upper limit of their thermal flight threshold) progresses from November to March each year. 2.Minimum relative humidity was below 35% for several days, and Focus of study was to determine microclimatic conditions that monarch butterflies experience 3.The rate of water evaporation was higher than 30 which determines their local movement to lower ml/week elevations. Monarchs abandoned opened areas first, followed by those clustered in closed forest areas. Methods • Derived a Closed/Open Index (tree density, total basal area, and forest overstory density in 75 quadrats, 10x10m), • Monitored daily changes in temperature, humidity, and wind speed in closed and open areas during most of the 1993-1994 season, and • Experimentally compared the rates of water evaporation in areas near monarchs clustered in closed and open forests 40 Monarchs abandoned location Closed 30 Opened Conclusions New data substantiates previous evidence that forest thinning is detrimental to monarchs due to 20 higher rates of desiccation, exposure to more extreme temperatures and higher lipid expenditures. 10 References: Rate of (ml/wk) Evaporation Rate Water Calvert, W.H. & Brower, L.P. (1986). The location of monarch butterfly (Danaus plexippus L.) overwintering colonies in Mexico in relation to 0 topography and climate. Journal of the Lepidopterists' Society, 40, 57 65 73 81 88 95 102 109 116 123 130 137 144 164-187 Days of Overwintering .