By Gail Morris

May 09, 2019

An Early Milestone!

Monarchs conquered the mighty Sierra Nevada mountain range this week with the first sighting of a monarch reported on May 4th in Reno, Nevada! This early first sighting arrived six days earlier than in 2018 and a full 21 days earlier than in 2017. Meanwhile monarchs crept north in Arizona moving into Sedona, just south and down the mountain from Flagstaff. Monarchs are now slowly expanding their range in the West.

Southern California Monarchs

When you look at the Journey North Monarch Adult (First Sighted) Map, did you ever notice that there always seems to be monarchs reported along the coast of Southern California? Why? Scientists are curious about these monarchs, too. Do they migrate or not?

Could the weather make a difference? Last week we mentioned deserts and dry air. But the Southern California monarchs from San Diego to Los Angeles live in a marine climate, with moist winds frequently blowing inland from the ocean. The air here is more humid and the daytime high and nighttime low temperatures are much closer together. As moist ocean air swirls inland, it eventually hits the nearby mountains and is uplifted. This makes it colder. Like the water drops that condense on a cold drink, much of the moisture in the air falls as rain along the coastal mountains of California. As the air continues its journey, it rushes down the slope on the other side of the mountain. This makes the air warmer, so places like Palm Springs are hot and dry. You can see this movement in the diagram on the right.

There are some parts of Southern California that have monarchs much of the winter. Steve Engel in Huntington Beach is still seeing them now.

“Brand new Monarchs are all over Huntington Beach, California!”

Wayne Centers lives in Riverside and said he hadn’t seen an adult monarch since November 27th. Then on January 26, one appeared. He’s wondering where these monarchs come from, too.

“Too bad this one wasn't tagged. She sure traveled a distance. If I had to guess I would think California desert or Arizona.”

Migrating to Breeding?

Dr. David James, Washington State University, directs the Monarch Butterflies of the Pacific Northwest based in the state of Washington. In a paper published last year, Dr. James reported that one of the migratory monarchs tagged in the Northwest in the Fall was found breeding in Southern California.

“I think in most years in the West (in the past) the number of individuals joining the winter breeding population in Southern California has been small. But with migrants now encountering, in general, warmer conditions when they arrive in Southern California, this number may have grown. Just one individual, but perhaps representative of a significant subset of the migratory population. In recent years, there have also been scattered reports of winter monarch breeding around San Francisco and in the central Valley. So, if this is a real and growing phenomenon, it may be a further explanation for declining numbers in overwintering (clustering) population."

“Anecdotal evidence [personal reports] suggests that the winter breeding population in Southern California is now larger than it used to be and covers a wider area. It seems it may extend from the Mexico border right up to Santa Barbara whereas previously it was all south of Los Angeles. I think its extent varies annually of course but it appears to be generally increasing as autumn/winter becomes warmer in that area.”

New Study Results Soon!

Dr. Francis Villablanca, Cal Poly, San Luis Obispo, oversees the Monarch Alert tagging program in coastal California. We often think of tagging monarchs to see where they migrate to each Fall. But tagging monarchs can also help us learn if monarchs are staying in one location rather than migrating.

“The main focus of Monarch Alerts’ tagging program is to map where and when Monarch butterflies are breeding in Southern California. We have really good tagging data that shows monarch butterflies breed in Southern California year round. Currently, we are trying to establish the geographic limits of year-round breeding.

“It is fairly easy to document year-round breeding because we see evidence of it. Meaning, we can observe it. The problem is in demonstrating where year-round breeding does not occur, because “not breeding” is not something that can be observed. Meaning, it could be happening, but we failed to see it, versus it’s not happening, therefore will fail to see it. Instead we need a really large survey effort, and to show that in spite of that effort, some areas do not have year-round breeding.”

Dr. Villablanca hopes to have something ready for publication by the end of this year. It will include three years of data and it may answer some of the questions!

Where Next?

Where will Western monarchs appear next? Keep an open eye and share what you see here on Journey North!

Please Report Your Sightings

Help us to find answers to these and other questions. Let’s keep following monarchs and their movements throughout the West. Please join Journey North and our partners who care deeply about the western monarch butterfly population to help track monarchs. Report your sightings on Journey North – sightings can include first adult monarchs, eggs, larvae, and first milkweed emergence.

Gail Morris is the Coordinator of the Southwest Monarch Study (www.swmonarchs.org), a Monarch Watch Conservation Specialist, and the Vice President of the Monarch Butterfly Fund and the Central Arizona Butterfly Association. The Western Monarch Population News is based on comments provided to Gail Morris. We hope to increase the number of sightings and therefore photos and comments entered into the Journey North. We rely on the volunteers who communicate regularly with Gail and who agree to participate in our effort to increase awareness of the population of western Monarchs.