Monarch population size over winter 2016-2017 announced!

The estimates of the monarch butterfly overwintering population were announced Thursday February 9th by WWF Mexico.  The butterflies are so dense at their dozen or so mountain-top clustering sites that overwintering butterflies cannot be counted.  Instead, the area of forest that is densely coated with butterflies (at about 5,000 butterflies per square meter looking up into the canopy) is estimated as a measure of monarch abundance.  Butterflies arrive to Mexico around the day of dead in November and stay until March each year.

This winter season (2016-2017), there were approximately 2.9 hectares of forest occupied with dense monarchs (somewhere in the neighborhood of 145,000 million overwintering butterflies).  This estimate is down some 27% compared to last year.  Nonetheless, the previous two years were a 600% increase over the all-time low populations (2012-2014).

Where does this leave us?  The good news is that this year’s population was higher than predicted by many.  The season started with a late spring storm that killed an estimated 5-10% of monarchs in March 2016, and many reported low numbers of adults last summer.  Nonetheless, the lower numbers this season compared to last are within the range of year-to-year variation, and overall, the population seems to be relatively stable over the past decade.  With these 24 years of data, there are various ways to plot and assess the data.  Below I have plotted the four year averages for six periods beginning in 1992.  Any way you slice it, the trend has been negative, and the population is not nearly what it was.  Nonetheless, the downward trend seems to have lessened this last period.    Is this the new norm?  How dangerously low are these numbers? And what can we do to reverse the trend?

 

10 Replies to “Monarch population size over winter 2016-2017 announced!”

  1. Hi I have taken the seeds for milk weed and spread then last year. Is there anything else I can do to help? I want my grandchildren of the future to have these magnificent butterflies around. This year I am not seeing many and am hoping I’m looking to early! I’m not sure when they should be here, but I have noticed fewer each year here in nj. Thank you for all you do to help these beautiful creatures.

  2. Are the monarchs in danger of extinction, or just their migration process? I know people can breed monarchs at home and butterfly zoos do this often.

    • Thanks for your question… as a species, monarchs are not in danger of extinction — but you are right, their spectacular migration in the eastern USA has been declining for the past 22 years. Monarchs have been introduced to Spain, Hawaii, Australia, and New Zealand… they exist there as non-native species.

      • Thank you for your reply.
        Do the monarchs that are domestically bred still attempt to migrate to South America in the autumn or do they lose that instinct? Or has this never been studied?

        • It has *not* been well-studied, but most evidence points to the notion that most all monarchs would try to fly south in the fall if reared in that environment. In other words, there does not seem to be much evidence for a genetic loss of migration. The environmental cues of shorter days, cooler temperatures, and declining milkweed quality all signal physiological changes associated with southern migration. I talk a bunch about this in my book. All the best, -Anurag

Leave a Reply

Your email address will not be published. Required fields are marked *

*