Monarch Monitoring Results

 Here's a cool synthesis paper using data from the Integrated Monarch Monitoring Program (IMMP).  The headline conclusion is that ROWs had the most milkweed plants:

Site Type: ACL, Agricultural Conservation Land; DEV, Developed; PGS, Protected Grassland; ROW, Rights-of-way; UGS, Unclassified Grassland. 

However, this paper excludes Asclepias subverticillata (and A. verticillata), the most common milkweed species in our area.  Apparently this was so they could apply their total stems to the work of Thogmarten et al that calculated how many stems of milkweed are needed to support stable monarch butterfly populations.  But, since the main results of this paper compare milkweed plants between different site and habitat types, they should at least show what this analysis would look like with A. subverticillata.  

Actually, most of the paper's results are focused on Eastern U.S., and there is a companion Western paper forthcoming, but that is not obvious from the Abstract.  So excluding a common western milkweed plant may not have changed most of the results.  

What's also not obvious is that none of the figures show actual data, they only show the model results derived from the data.  Apparently that is how ecology works now-a-days:  create some kind of bespoke complicated statistical model and don't even bother to plot the underlying messy real-world data...

Citation

Front. Ecol. Evol., 23 May 2024

Sec. Conservation and Restoration Ecology

Volume 12 - 2024 | https://doi.org/10.3389/fevo.2024.1330583

Popular plants for Monarch butterflies in Northern Arizona

**Updated 11/16/2022 

As of November, 2022, there were 260 observations on iNaturalist of monarch butterflies in the northern half of Arizona - basically everything north of Phoenix.  I analyzed these observations to try to identify which plants are most important nectar food sources.

iNat link.

I filled in the Life Stage annotation for all larva and pupa.  There are 62 observations of larva (caterpillars), 1 observation of a pupa, and 197 observations of adult butterflies.

The number of monarchs photographed each year has declined from a high of 75 observations in 2015 to an average of 55 a year in 2021 and 2022.  Since the number of iNat users and observations has increased more than 100x since 2014, it seems that the last 2 years represent more effort with less observations, indicating a possible decline in abundance.

For the adults, I annotated the observations using the Observation Field "Nectar / Pollen delivering plant" when I could ID the flower the monarch was observed on.  In some cases, the adult could be observed drinking nectar; in many other cases I assumed that a monarch adult resting on a flower was obtaining nectar.

In total, 71 adult monarchs appear to be drinking nectar from flowers that are identifiable to species or genus.  I documented 27 different plant species being used as nectar resources by monarchs.  This is a large diversity of plant species, considering that this data set included only 71 total observations of monarchs on flowers.

iNat link.

By far the most common plant species was Asclepias subverticillata, the common weedy milkweed species of northern AZ, and also a great plant for monarch caterpillars.  It is possible that some adults were just resting on the milkweed flowers in the process of depositing eggs on the plants, rather than drinking nectar.  Either way, clearly milkweed are important to monarchs.  This species is also popular with a diverse group of other pollinating insects.

Several aster species were also common nectaring plants, as well as butterfly bush (Buddleja), a planted ornamental that apparently lives up to its name!

Monarch presence in Northern Arizona is strongly seasonal, with most adults observed in late summer (August-September), so it is not surprising that some of the late summer Asteraceae such as Ericameria, Helianthus, Bidens and Heliomeris are popular nectar sources.  Since monarchs are generalist pollinators, this data could be consistent with opportunistic (no preference) nectaring.

However, there are many other common plant species flowering during September (such as Gutierrezia sarothrae, Dieteria canescens, Datura wrightii, Purshia stansburyana, Verbascum thapsus, Geranium caespitosum, Achillea millefolium), and no monarchs in this data set were observed nectaring on them. This suggests that monarchs do prefer certain species over others.

Also, there is the question whether the adults observed on flowers during August--October are migrating adults, mating adults, or newly metamorphosed adults.  Given that we do see caterpillars in September, and it takes about 30 days for a monarch egg to grow into an adult, it is likely that all three types of adults are making use of nectar resources in Northern Arizona.  

Caveats and Conclusions

Any mistakes or omissions are my own. I may have misidentified some flower species, but I don't think that would change the overall conclusions.

The small sample size limits the conclusions that can be drawn; more observations are urgently needed to better establish monarch plant preferences.  

Also, this data is subject to the biases of  the "citizen scientists" who use iNaturalist to document biodiversity.  They may be more likely to photograph monarchs on showy flowers, in areas near their homes (landscaped yards and ruderal/disturbed natural environments), and at convenient times of day.

Therefore, this study might be best used to help guide planting decisions to support monarchs in areas near where people live.

Acknowledgements

Thanks to iNaturalist user jdmore who created an excellent wiki explaining how to use the iNat search URLs to filter results, which was a crucial step to analyze this data.

Also, thanks to all of the iNaturalist community, including the 107 people who observed monarchs in the study area, and the 123 people who helped identify them.

Arizona Monarchs Visit California and Mexico

 Five years ago my wife and I joined other local citizen scientists at Willow Lake for an enjoyable afternoon catching and tagging monarch butterflies.  The tags are small stickers with ID numbers.  They  don't impair the butterfly's ability to fly, but they do let us humans track where they fly to!

A monarch in the hand.

 The Southwest Monarch Study group recently updated their map showing the location of recovered tags.  The straight lines indicate starting and ending locations, not necessarily the meandering paths monarchs take to migrate across the landscape. 

Image from Southwest Monarch Study.  

  Over the ensuing years, those tagged butterflies have turned up as far away as the monarch's overwintering grounds in Mexico. Interestingly, they also visit California overwintering sites.  Most monarch populations can be neatly divided into Eastern and Western populations based on where they spend the winter; Eastern go to Mexico and Western go to California.  But it seems AZ monarchs can go to either, which raises the fascinating question: how do they decide where to go?  Is AZ a meeting spot for different populations, and each return to their home wintering sites, or is AZ a melting pot, a single population where individuals decide each year where to overwinter?

Hopefully this citizen science research will help resolve some of the question marks on monarch migration maps.

Monarch migration map from Xerces.

Monarch migration map from Monarch Watch. 

Monarch Decline Blamed on Changing US Agriculture

Graph of returning migration Monarch Butterflies from MonarchWatch.org

CBS quoted entymologist Lincoln Brower: "The main culprit," he wrote in an email, is now genetically modified "herbicide-resistant corn and soybean crops and herbicides in the USA," which "leads to the wholesale killing of the monarch's principal food plant, common milkweed."

The website MonarchWatch.org has the best in-depth analysis of the triple threat of habitat loss.  What to do?  Plant milkweed!

Do endemic taxa correlate?

One of the main assumptions of many biodiversity assessments and conservation efforts is that biodiversity correlates across taxa. In other words, an ecosystem with high plant diversity might be expected to also harbor high lichen diversity, high arthropod diversity, and a great many birds, bees, and bloomin' confusion. 

If this assumption is true, than scientists could study one taxa, say lichen, and use the results as a surrogate for studying all of the other possible taxa. But a new study by Dr. Che-Castaldo questions this "surrogacy" assumption:

"Testing Surrogacy Assumptions: Can Threatened and Endangered Plants Be 
Grouped by Biological Similarity and Abundances?"

Abstract:

"There is renewed interest in implementing surrogate species approaches in 
conservation planning due to the large number of species in need of 
management but limited resources and data. One type of surrogate approach 
involves selection of one or a few species to represent a larger group of 
species requiring similar management actions, so that protection and 
persistence of the selected species would result in conservation of the 
group of species. However, among the criticisms of surrogate approaches is 
the need to test underlying assumptions, which remain rarely examined. In 
this study, we tested one of the fundamental assumptions underlying use of 
surrogate species in recovery planning: that there exist groups of 
threatened and endangered species that are sufficiently similar to warrant 
similar management or recovery criteria. Using a comprehensive database of 
all plant species listed under the U.S. Endangered Species Act and 
tree-based random forest analysis, we found no evidence of species groups 
based on a set of distributional and biological traits or by abundances 
and patterns of decline. Our results suggested that application of 
surrogate approaches for endangered species recovery would be unjustified. 
Thus, conservation planning focused on individual species and their 
patterns of decline will likely be required to recover listed species."

Similar conclusions have been reached by a other studies. For example, Erhlich et. al. 2002 found that in subalpine meadows in Colorado, indicator taxa show no skill in predicting diversity of other taxa, even among phylogenetically related species (in this case, butterflies and moths).