Widespread declines in butterfly populations linked to climate: New study by Forister in Science

Apologies if there is already a thread on this paper but I couldn’t find one.

@dkaposi Recently added this important new paper by Forister et al. to the inat publications Wiki:

I wanted to highlight this paper for two reasons.

First the authors find a very concerning widespread decline in butterfly populations over the past few decades. Populations are seen to be declining across three separate datasets covering the Western US. The authors do a careful analysis to try and pin down the effects that climate change could be having on this decline. They find a consistent association with fall warming: warmer falls → fewer butterflies. The mechanisms behind this are kind of unknown but a very interesting question for entomologists to discuss. They also showed some effects of regional changes in precipitation on populations. I think this study may also put recent declines in Western Monarch butterflies in perspective. While monarchs get most of the public’s attention, perhaps their declines, while very dramatic, are not unique–unfortunately. Surprisingly this study did not find that development was a major driver of population declines, which is what I would have expected.

The second advance this study makes, is that the authors figured out a way to use the iNat data to quantify population trends. If you are data-minded, check out the the supplemental information of the study to see how the iNat observations were normalized to measure trends in butterfly populations while accounting for changes in iNat observation effort. ( There are more iNat observations every year as the user base grows so you cannot simply count iNat observations to conclude anything about populations! ) On its own the iNat analysis would not be very strong but it backs up the more systematically collected data and it is much more extensive. This paper gives ecologists a blueprint for how to use the iNat dat in this way.

Anyway kudos to the authors (including the amazing Art Shapiro) for this very troubling but important study. Thanks again to @dkaposi for bringing to my attention! Great use of the wiki!


While butterfly numbers are decreasing there observations are increasing.
Have a look at this.

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