Announcing! Listing the Monarch Butterfly under the Endangered Species Act? No.

The Endangered Species Act of 1973 (ESA), enacted under President Richard Nixon, is perhaps one of the greatest pieces of environmental legislation in the world.

Six years ago, in 2014, four entities petitioned the US Fish & Wildlife Service (F&WS) to list monarch butterflies as threatened under the ESA. The groups were the Xerxes Society for Invertebrate Conservation, the late Professor Lincoln Brower, the Center for Biological Diversity, and the Center for Food Safety. The CFS is an anti-GMO organization. In any case, when the F&WS dragged its feet in making the decision, in part because it is so overwhelmed by petitions and protection of endangered species and chronically underfunded), this group sued the F&WS and the result was that they were required to make their determination by December 15th 2020.

This morning, the F&WS announced that the monarch will not be listed under the Endangered Species Act, although listing as threatened was “warranted but precluded by work on higher-priority listing actions” according to the F&WS.

It is important to note that no credible scientists thinks that the monarch butterfly, Danaus plexippus, itself as a species is going extinct. In other words, there are hundreds of millions of butterflies, and the species as a whole is not at significant risk. Although native to the Americas, monarchs have been introduced and maintain self-sustaining non-native populations in places as far-flung as Spain, Australia, and Hawaii. Nonetheless, the petition to list monarchs was based on the “migratory phenomenon”, the annual migration that takes monarch butterflies four generations to go from Canada through the United States, to overwinter in Mexico for four months, and then to re-migrate back step-wise, beginning in the spring. It is a magical, unprecedented, and absolutely stunning natural event!

And, the ESA seeks to protect not only species, but also the ecosystems that allow species to maintain sustainable populations, and coverage of unique phenomenon such as the monarch butterfly’s annual cycle. Thus, the F&WS entertained this petition.

And to be clear, the monarch butterflies population has been steadily declining over the past 25 years, at least where we have the best data, which is in the bottleneck of their overwintering grounds in the highlands of Central Mexico. There, the forest area covered by monarchs is censused annually as an estimate of their population size. although this only represents one generation of the four that the monarchs make annually, because most butterflies must pass through this in Mexico, it represents an important pinch point in the annual migratory cycle.

With 27 years of data, there are various ways to plot and assess the trends.  Above I plotted four year averages for seven periods working backwards. Any way you slice it folks, the trend has been negative, and the population is not what it was. Nonetheless, the extreme downward trend seems to have bumped up in the last period of four years. Is this the new norm, a winter population hovering between 2 and 4 hectares of dense butterflies, perhaps representing 50 million butterflies?  How dangerously low are these numbers? And what can be done to continue to reverse the trend and buffer the population?

So, what does this all mean? The listing decision was a highly controversial one. Many serious scientists that support monarch conservation efforts were against the listing. There are many reasons behind that, including the extreme difficulty of implementing protections of an animal that covers nearly every square mile of non-forested land east of the Rocky mountains! In addition, the tremendously high abundance of the butterfly in general, even if recently declining, puts it in a decidedly different category than other threatened plant and animal species.  And, the F&WS is committed to continue to evaluate this listing decision into the future.

Understanding the mechanisms of the monarch’s decline has also been debated. I have written extensively about it in two publications, one published in Science in 2018 and the other in PNAS from 2019. Other topics on the biology and conservation of monarchs are covered in my popular book, Monarchs and Milkweed (Princeton University Press),  newly available as an audiobook. As with many things on this iconic insect, a symbol of nature, a sentinel of the health of our continent, and with staggering momentum in the public’s eye, this decision will echo far and wide. Nonetheless, we must stand firm in our trust of the scientists studying the monarch butterfly, and studying conservation of our wildlands and species much more broadly.

Best wishes, -Anurag