Desert Refuge Project

Hello USA-NPN,

Our Desert Refuge: Monarchs and Milkweeds in Arizona project is coming to a close for southern and central Arizona. If you are still seeing monarchs, you are welcome to continue to record data, as these observations are valuable to our understanding of monarchs in the state. However, we asked for a winter time commitment to better understand overwintering behavior, and you all provided that! For those in northern Arizona, where the milkweeds and monarchs are now becoming active, we would love to have you start recording data! 

Below, we take a look at what we learned from your data from the past nine months, and share next steps for this project. Thank you so much for taking part in this effort to help us better understand overwintering behavior of monarchs and the milkweeds on which they depend! 

Photos below of rush (desert milkweed) flowers or flower buds and open flowers at the University of Arizona. On the left, can you find the tiny monarch caterpillar in the lower cluster of flowers? On the right, flower visitation by an adult monarch.

What you reported this year

This year, 53 observers reported data on both monarchs and milkweed. Eight other observers reported only on monarchs, and seven tracked only milkweed. The map below shows locations where observers reported monarchs (Danaus, orange x) or milkweeds (Asclepias, blue square), or both (orange x on top of blue square) across the state.

We are so grateful to both our backyard observers and the Local Phenology Programs who have contributed data to Desert Refuge! The table below shows all of the records that our LPP partners have contributed since last September at the start of the overwintering season. Reid Park Zoo Pollinator Garden finished off the year at the top of the list with over 3,600 observations, followed by Desert Botanical Garden and Tohono Chul. We also had 44 independent observers participating in this project. Thank you all for your efforts!

The majority of our observers are located in the two metro areas of Phoenix and Tucson. We saw some differences in the activity of monarchs and milkweeds in these two locations this year. The map below shows observers reporting on monarchs and our three most common species of milkweed in the Phoenix area.

In the Phoenix area, observers reported adult monarchs throughout the winter months, with the most recent reports in June. Observers reported monarch caterpillars starting in late September through early February.

Looking more closely at your reports in the Phoenix area, we can see that across all milkweed species, your reports of young leaves spiked in mid-October, and then started increasing again in January. Your reports of open flowers peaked in late September and then started increasing again in mid-March. Your reports of adult monarchs peaked early in the fall, while your "yes" reports of caterpillars were highest in mid-November.

The map below shows Tucson-area observers reporting on monarchs and the most commonly observed milkweeds.

Tucson observers also reported adult monarchs throughout the year. Observers started reporting monarch caterpillars a few weeks later than observers in Phoenix. While observers in the Phoenix area stopped reporting caterpillars in February, observers in Tucson continued to report caterpillars throughout the spring up through the end of May.

Looking more closely at your Tucson-area reports, your reports of young leaves stayed fairly consistent all winter, while open flowers peaked in early September and again in early May. Your reports of adult monarchs stayed fairly consistent all winter, with monarchs recorded on 10-30% of visits. Caterpillars were more likely to be recorded between mid-October and the end of May.

What's next for Desert Refuge?

We are left with several questions that we will be tackling in the coming months - what is the overlap in milkweed phenology and monarch activity on an individual site basis? Do monarchs have a preference for milkweed life cycle stage, such as presence of flowers, for laying eggs? Did weather conditions influence the higher observed activity in monarchs this year?  

We plan to continue Desert Refuge next winter. We are exploring adding one other set of data that has to do with microclimates. Weather data is often taken from weather stations, but our urban gardens may not match weather station data closely.  To test this, we would ask a handful of people to place a data logger for temperature and humidity near their milkweed and use an app to send us data periodically. If you would be interested in participating in such a trial, please email Kim Pegram (

We will keep you updated as we learn more from your data. Thank you for your contribution to this important project!


Erin Posthumus

Outreach Coordinator

USA National Phenology Network

Kim Pegram

Program Director, Pollinator Conservation

Desert Botanical Garden

Natalie Melkonoff

Plant and Insect Ecology

Program Manager

Desert Botanical Garden

This project is generously supported by a Partner Grant from Monarch Joint Venture and U.S. Forest Service International Programs.

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