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Why The Monterey Bay Area Matters To Monarch Butterflies

Erika Mahoney
Visitors meander through the Monarch Butterfly Sanctuary in Pacific Grove. It's an overwintering site for monarch butterflies.


It’s that time of year again when thousands of western monarch butterflies begin to show up in the Monterey Bay area to spend the winter. They come from all over the western United States and southwestern Canada. 

KAZU’s Erika Mahoney spoke with Jessica Griffiths, who has worked with monarchs in Monterey and San Luis Obispo counties for almost twenty years. She’s currently a Senior Biologist for Althouse and Meade, Inc., an environmental consulting firm in Paso Robles. Griffiths used to work closely with the Pacific Grove Museum of Natural History. 


Erika Mahoney (EM): What about the Monterey Bay area attracts monarchs?


Jessica Griffiths (JG): The Monterey Bay Area has the perfect climate for overwintering monarch butterflies because they need to come to a place that has a moderate winter temperature that does not freeze, but it's not too hot. So we're talking sort of a Goldilocks situation here. They also need moisture. So the winter rains and fog are also really great for them. 


EM: What’s “overwintering?”


JG: Overwintering is when an animal or a plant survives the winter by either sheltering in place somewhere or burying themselves or hiding in a den or in a tree hollow. It's just a term to describe what an animal does to make it through the winter. 


EM: We don’t tend to see monarch butterflies all over our area, but rather in specific spots like the Monarch Butterfly Sanctuary in Pacific Grove. Why is that?


JG: Monarch butterflies do come to the area because the climate is right, but they don't just cluster in any old spot. They're looking for a very specific set of conditions. And what they're honing in on is the microclimate in an area and the microclimate, that just means the climate conditions at a really specific location. So they need exactly the right temperature, humidity, sunlight, intensity and wind speed. And actually the arrangement of trees is really important in creating those conditions. 


EM: Can you just describe what a cluster of these monarchs looks like for our listeners? 


JG: Yes. Monarch butterflies overwinter in dense clusters. And what that looks like is they will actually gather together in the trees, in the tree branches, and they will pack really tightly together with their wings closed. And they actually look just like clumps of dead leaves. So the undersides of their wings are sort of a dull beige color and they're really easy to walk right by. I've actually missed seeing clusters when I've been out looking for them. As the day warms up, they begin to open their wings and you start to see a flash of orange. And then when they start flying around, that's when you really see the colors.  


EM: Monarch butterfly numbers have been drastically declining. What are the top reasons for that?


JG: Western monarch butterflies are really in trouble right now. Their population has really crashed in the last few years and it's primarily due to habitat loss and that's habitat loss of their breeding habitat, which is milkweed. Milkweed is the only plant that the monarch caterpillar can eat. Also, habitat loss of overwintering areas. So the areas along the Central Coast of California where the butterflies come to spend the winter, many of those areas have either been lost to development or drought. Another thing that is driving that decline in monarch butterflies is actually climate change. Our winters are getting hotter and the overall temperature is increasing. 


EM: What can we do to help? 


JG: One thing people can do is to plant nectar plants for monarch butterflies and to plant native milkweed. So if you live on the coast, if you live in Pacific Grove or you live in Monterey, planting nectar plants for monarch butterflies to feed on when they arrive in the fall and as they're getting ready to leave in the spring is huge and can really help them. If you live farther inland away from the overwintering sites, you can plant native milkweed. You can also do everything you can to reduce the amount of pesticides that you're using around your home, in your garden. Go organic and buy organic when you can, because the fewer pesticides we use, the better. 


EM: These monarch butterflies are really beautiful and so small and delicate. Why should we care about these creatures? 


JG: You know, I do get asked that, why do we care about monarch butterflies? I think that monarch butterflies are so special and unique. They're really the only insect that does this kind of a long distance migration to gather in huge numbers and spend the winter. It really is a unique natural phenomenon, aside from the fact that they are a really important pollinator as well. They pollinate our native plants. They're actually part of the food chain, the monarch caterpillars are really important in the milkweed community. They are important prey for actually quite a few different insects. So they're part of the web of life. But, they're just a really unique and special organism. And I think they deserve our protection. 


EM: How do monarch butterflies make that long distance migration?  


JG: It's really incredible. When you look at a monarch butterfly, they just look so small and delicate and you just can't believe that something like this could navigate hundreds of miles. But they do. These butterflies are coming from all over the western United States and some of them from southwestern Canada as well. They are amazing navigators. So monarch butterflies actually have an internal compass, which is in their antenna. They also have an internal clock that they can use to basically tell time and they can sense the magnetic field of the earth. They can also see polarized light and they can use the position of the sun to navigate, to tell what direction to fly, just like ancient human sailors and some modern human sailors do. So they have a whole toolbox, which they can use to navigate and get to where they need to go. 


Senior Biologist Jessica Griffiths is giving a Zoom presentation for the Pacific Grove Museum of Natural History’s Hardcore Natural History Series on November 12. The event is called Small But Mighty: Monarch Butterfly Migration and Overwintering.


You must register by 5pm November 12 to attend. 

Erika joined KAZU in 2016. Her roots in radio began at an early age working for the independent community radio station in her hometown of Boulder, Colorado. After graduating from the S.I. Newhouse School of Public Communications at Syracuse University in 2012, Erika spent four years working as a television reporter. She’s very happy to be back in public radio and loves living in the Monterey Bay Area.