Living Acres

Monarch Butterfly Population Numbers of 2016

October 28, 2016

Monarch Numbers

Since 1993, butterfly researchers have been keeping records of the monarch population size. In 2013, an all-time low of 0.67 hectares (approximately 32 million monarchs) was documented. This record-setting low is likely the result of a cold period during the first three weeks of May 2013, which restricted movement of the monarchs into the northern breeding range.

To calculate monarch population size, scientists measure the area of forest covered by monarchs while they overwinter in the oyamel fir forests of Mexico. Researchers flag off the areas and determine the amount of hectares the monarchs are covering, which is then used for the official measurement.

In the winter of 2015-2016, good news came from Mexico. Researchers recorded 4.01 hectares of monarchs. This rise indicates nearly 200 million monarchs were blanketing the oyamel fir forests. This significant increase brought the 1994-2016 monarch population average to 5.91 hectares. For the monarch population to be considered stable, a consistency of 6 hectares must be met.

Unfortunately, it does not appear that this upward trend will continue. According to Monarch Watch, all of the data collected on current monarch populations suggest that 2016 will be a near repeat of 2014 due to a late spring weather event in Mexico that drastically reduced the number of adult monarchs making the journey north. They calculated a dismal number of 1.13 hectares. It is unlikely that the overwintering numbers will surpass 2 hectares.

The low number of monarchs that moved north from Texas in early summer, which resulted in these low-sighting numbers, reflect the mortality rates from a heavy sleet storm that swept through the oyamel forests in early March. While some butterflies had already started their migration north at that time, a majority of the overwintering population had not yet departed.

Rather than a discouragement, this decrease should act as a motivation. All landowners can still take steps to promote monarch development, including planting native milkweed in their gardens and non-cropland areas.

As the year goes on, check back for updates on the final overwintering number for the 2016-2017 winter. Stay informed by visiting


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