On January 19, the official announcement of the number of monarchs seen during the annual Thanksgiving counts at California overwintering (OW) sites in 2020 was made. The news was not good. After our routine family visit to selected overwintering sites at Thanksgiving, I made the prediction that there would be less than 2000 total butterflies at the sites. Unfortunately, I was correct. The official number counted was 1914. This is down from around 30,000 in 2018 and 2109 and about 220,000 in 2017. While this is undeniably shocking and cause for concern, the picture may not be as bleak as the raw numbers suggest.

There is apparently, this winter, a much larger population of breeding Monarchs in southern California and also in the San Francisco Bay Area. Evidence for this is harder to obtain of course but I will provide some here.

I have been involved with Monarchs for 43 years, and the single, overriding thing that I have learnt is that the Monarch is a highly adaptable creature! It has an incredible ability to adjust to changing environmental circumstances. In Australia, it took less than 100 years after its introduction to change its core physiology as part of adaptation to a different climate. Adapting to man-made environmental challenges may take Monarchs a while but I believe it can happen. I believe that the widespread and intensive use of neonicotinoid insecticides is one likely factor behind the current Monarch population decline. But even with insecticides, insects can develop resistance over generations. The few Monarchs that are alive and well in California currently are the ‘survivors’, those that have beaten the perils stacked against them.

Clearly, we need to try and make life as fruitful as possible for these survivors, to aid in their population recovery. These Monarchs will produce progeny that are also ‘fitter’ than the general population and we need to ensure that milkweed is there for them, particularly during spring in California.

The Monarch as a species is particularly good at ‘trying different things’. Thus, while the majority of the population does one thing (like migrate and overwinter), there is always a significant subset exposed to the same environment, that ‘decides’ to do something different, like not migrate. Most of these of course will die but in some circumstances, some locations, the outcome may be good, giving another option for continuation of the species, should it become necessary. We may be seeing this now with the rise in winter breeding of Monarchs in warmer parts of California like the LA Basin and SF Bay Area. There is also evidence for the first time of breeding winter Monarch survival in far south-western Oregon.

Here is some circumstantial evidence for the notion that Monarch butterflies this winter are behaving differently in California than normally seen. That is, more of them seem to be engaged in breeding activities and fewer are overwintering in a non-breeding state at overwintering sites.

We have been running our WSU-PNW Monarch-tagging program since 2012 and each year we have tagged between 1000 and 6000 Monarchs. During 2012-19, a total 122 tagged Monarchs were recovered and the majority of these (63%) were found at overwintering sites in California.

In 2020, we tagged nearly 1300 Monarchs, and to date, zero have been found at overwintering sites! This is despite the tagged 1300 Monarchs representing around 65% of the total number of Monarch butterflies seen this year at overwintering sites!

Since 2014, our overall annual average recovery rate for tagged Monarchs has been 0.66%. In 2020, this recovery rate was 0.77%. That is, we recovered as many tagged Monarchs as we could expect to. The difference was that they were all found during migration instead of at overwintering sites. The number of tagged Monarchs we recovered during migration in 2020 was eight times greater than the average for the previous six years.

Most tag recoveries in 2020 were made in inland Northern CA and in the Bay Area. Unlike other years, tagged Monarchs apparently did not move coastward to overwintering towns like Santa Cruz and Pacific Grove. I suspect many stayed in the Bay Area and joined reproductive populations. In 2019, we obtained photographic evidence of a tagged migrant from Oregon laying eggs on milkweed in a Bay Area back yard. In 2020 a male tagged Monarch from Oregon was photographed (see below, credit Teresa Chang) feeding on milkweed at Benicia in the Bay Area.

These data from our tagging program suggest that in this year at least, many migrating Monarchs that were headed to overwintering sites contributed to a Bay Area breeding population that is, from a number of reports, quite substantial this winter.

Assessing the extent of the winter breeding population of Monarchs in the SF Bay Area is not an easy thing to do. It is far easier to go to overwintering sites where the monarchs conveniently gather en masse so they can be counted! A breeding population is distributed across the landscape. However, just like we have done with the WSU-PNW tagging program, it is possible to harness data collected by citizen naturalists.

iNaturalist is an online resource that anyone can use to record their observations of fauna and flora. Established in 2008 by the California Academy of Sciences in San Francisco, it now has more than a million users worldwide, many of them in California. It is possible to extract data from iNaturalist collected on the occurrence of Monarch larvae and pupae in the SF Bay Area going back almost a decade. This is what I did, focusing on the winter months of November/December looking at the observations made annually in these months since 2015.

During 2015-2019, there were 2-10 observations each year of larvae/pupae during November-December in the Bay Area (average: 6.2). In 2020, there were 66 observations of Monarch larvae/pupae in the Bay Area during November/

December! This is shown graphically below. Of course, the use of iNaturalist likely has increased this year due to Covid and the related growth of interest in natural history, but I doubt this dramatic increase in Monarch observations is solely due to this.

Again, this evidence is circumstantial and clearly some serious scientific monitoring of Bay Area milkweed patches, both wild and domesticated, is needed in future winters to obtain hard data. Anecdotally, native Showy milkweed is also remaining viable longer and is being used in some instances by winter Monarch larvae in the Bay Area.

Combining the data on tagged Monarch recoveries in the Bay Area with the above observations from iNaturalist presents a signal, I believe, of a changing dynamic in Monarch butterfly overwintering ecology in the western US. I think the primary driver for this change is likely to be increasing temperatures in California particularly in the ‘urban heat island’ areas of Los Angeles and San Francisco. Instead of seeing a shift northward of overwintering sites, perhaps we will see a sustained increase in winter breeding in California.

Brookings, Oregon is nestled in the far SW corner of Oregon. If adult Monarchs were able to survive the winter in the Pacific Northwest, Brookings would be the place to find them. Freezing temperatures are rare and average daily maxima for December-January hover around the mid-fifties which is the minimum temperature at which monarchs can fly. With a little bit of sunshine, Monarchs can rapidly elevate their body temperatures way above the ambient temperature. However, it’s the relative lack of sunshine during winter in Brookings which may be the limiting factor.

This year, for the first time, Monarchs have been reported flying in Brookings in January! One was sighted on January and had been reared and released in Brookings in late October. They were part of a late generation of caterpillars eclosing into conditions that were not strongly inductive for migration. The prime cue for inducing southerly migration is most likely the rate of daylength decline, and this rate in late October is sub-optimal for migration. Thus, these butterflies remained in Brookings to attempt survival as breeding adults. In most years this likely ends in failure because of cloudy, cool and wet weather, but this year, apparently some have survived. In addition, it is possible that immature stages may also be able to survive with milkweeds (mostly tropical milkweed) remaining green.

5 (photo below) and two others seen a few days later. Two were tagged

It is uncertain whether the small population of Monarchs will ultimately survive the winter in Brookings this year, but I think we are edging closer to a time when they will. The Brookings situation is an excellent example of Monarch adaptability, whereby there is a small proportion of the fall population that spurns migration, in favor of gambling on winter breeding. The Monarch is one of nature’s big gamblers, and in the quest for continued survival of the species in the chaotic casino of the 21^st Century, this must be a good thing!

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