Encouraging news from Mexico's overwintering monarch forests was released today. Fourteen colonies occupied 6.05 hectares (15.95 acres) this winter, a 144% increase over the 2.48 ha (6.13 ac) occupied last year. Population size in Mexico is derived by assessing how much area is occupied rather than by direct census of individuals. Key points are as follows.
- The studies were conducted in Michoacán and the State of Mexico in December 2018 and January 2019 by experts from the CONANP and the WWF-Telmex Telcel Foundation.
- Butterflies occupy 6.05 hectares of forest in the current hibernation period compared to 2.48 hectares reported in the same period of 2017-2018.
- A colony was registered for the first time in the Ojo de Agua ejido, located in the Nevado de Toluca.
In the Monarch Butterfly Reserve, the largest colony with 2.46 ha (40% of the total) was recorded in the El Rosario ejido (Sierra Campanario sanctuary) and the smallest (0.01 ha) in the Contepec ejido (Cerro Altamirano sanctuary) , both in Michoacán; while in the State of Mexico a colony greater than one hectare was reported in the El Capulín ejido (Cerro Pelón sanctuary). Outside this region, near the Popocatépetl volcano, a colony was recorded in Atlautla, State of Mexico, which occupied a forest area of 0.01 hectares.
Monarchs have been imperiled throughout North America for at least two decades. This year’s population census of the western subpop that overwinters in California was dismal (28,429 monarchs counted, an 86% decline from 2017). During summer 2018, high monarch abundance was observed for the eastern subpop, particularly in the north central US. But whether or not this abundance would be confirmed by an overwintering population increase was uncertain. Would monarchs die during migration and overwintering numbers still be low? Were the summer observations not representative of the entire eastern subpopulation of monarchs? The only official count for both the western and eastern subpopulations are in winter, so summer observations are anecdotal although they can suggest trends. This year’s anecdotes became an official WOW.
Several different issues drive this winter’s high population census, some are intentional and one is luck of the draw. Fortunately, 2018 spring weather in the migration corridor was favorable. Monarchs concentrated their early breeding in the center of Texas where conditions supported a high survival rate, thus providing a solid population base for subsequent migrating generations as the monarchs moved north. The intentional efforts to enhance breeding habit by increasing milkweed availability, to increase nectar habitat by planting high value (often native) wildflowers, and coordination with farmers to leave pollinator strips adjacent to crops all improved the summer range conditions.
At the overwintering end of the monarchs’ life cycle, the pine and oyamel fir forests in the high mountains are the preferred roosts for monarchs, protecting the clustered butterflies from temperature extremes and precipitation. Monarchs depend on the protection of these trees within a continuous forest habitat.
...degradation of pines and oyameles in the core zone of the Monarch Butterfly Reserve has stopped, according to the forest monitoring of 2017-2018, when it suffered damages in 6.7 ha, which represented a reduction of 57.6% in relation to the 15.8 hectares degraded in 2016-2017.
Monarch conservation requires attention at all phases of the butterfly’s life cycle. This means the northern summer habitat in the U.S. and southern Canada, the overwintering sites in Mexico, and within the migration routes between the two ranges.