Monarch Program News

Southwest Fire Storms Thwart Monarchs’ Arrival

David F. Marriott, Ph.D.
La Mesa, California
Executive Director, The Monarch Program
November 2003

Monarch butterflies begin gathering at overwintering sites along the southwest coast during the third and fourth week of October every year. In late October and early November the Santa Ana winds influence arrival times of monarchs from the northeast area west of the Rocky Mountains. The force of the winds captures the westerly movements of the butterflies and drives them into the coastal southwest. When the climate is warm, they hit the coast and fly northwest to a cooler climate. If the weather is cooler, including the absence of Santa Anas in late November and December, tens thousands of monarchs choose to overwinter along the coast south of Ventura County into Baja California, Mexico. Santa Ana winds rarely alter migration patterns of monarchs north of San Luis Obispo County.

The Santa Ana winds are a result of a high pressure zone above 5,000 feet altitude on the plateaus of Nevada and Utah. They reach the coast of California within two days. The winds condense and heat up, picking up speed as they intensify through mountain passes into southern California. Normally, winds in southern California blow toward the east, causing an onshore flow. Santa Ana winds reverse this course and raise temperatures.

The Santa Ana season ranges from September through April, but the winds are most common in October and November. Depending on the way they hit the Sierra Nevada, they can cut a wide swath from Baja California to as far north as San Luis Obispo County. Propelled by upper level winds, the air mass heads southwest. As they funnel through mountain passes, they pick up speed, a minimum of 10 miles per hour, often accelerating to hurricane forces up to 100 miles per hour. As their winds descend westward to seal level, they compress and heat up, about five degrees for every 1,000 ft. drop. When the winds reach the coast, they are usually only half as fierce, maybe 30 - 40 miles per hour, but temperatures rise over 20 degrees.

The timing of the Santa Anas this season was perfect for forcing tens of thousands of monarchs into the southwest. The high pressure system over Utah began building on October 22nd. By October 25th the winds arrived and so did the worst wild fires in the history of California. Many monarchs flying with the Santa Anas probably died when the fires started. Not because they were flying into the fire, although that may have happened, but because they were already in the fire area sipping nectar from flowers when the fires appeared. They were on their “last wing” to the coast and never made it.

In many places the fires consumed 6,000 acres per hour -- too fast for the flight of a monarch butterfly. By mid-December monarch researchers should have a better idea of how many were lost to the fire storms in the southwest based on annual population comparisons, tagging studies, and by monitoring the condition of the monarchs at overwintering sites in California during the Annual Thanksgiving Monarch Count. No overwintering sites were lost as a result of the fires.

Tagging experiments this autumn have already revealed important information near or in the fire areas in San Diego County. To date (mid-November), two tagged monarchs were reported that may help us understand more about their behavior during the fire:

1) Monarch tag #57085 was a male and released in the high desert at Scissors Crossing (Hwy. 78 & S2, San Diego County) on October 22nd. It was one of 31 monarchs (17 females and 14 males), released at 11:30 AM [33 deg. 05.904N -116 deg. 28.314W, elev. 2,247 ft.]. It was found dead on the morning of October 26th near Julian -- apparently a rock fell on it while drinking water from a mud puddle. The butterfly only traveled about 6 miles (straight line distance) but flew 2,200 ft. up the mountain in a southwest direction toward the coast. Later that day the fires reached Julian and destroyed the Kentwood community and woodlands where the monarch was found. If the other 30 monarchs chose the same route, they would have encountered flames and thick smoke nearly all the way to the coast. If this scenario is true, then all native migrants flying through Southern California mountain passes toward the coast perished where there were fires.

2) Monarch tag #57066 was a female released in La Mesa, California on October 11th. It was one of 16 monarchs (5 females and 11 males), released at 3:00 PM [32 deg. 46.044N -117 deg. 03.143W, elev. 492 ft.]. The butterfly was found alive and healthy 26 days later on November 6th in a residential backyard about 3 miles west of the release site. It was sighted resting on a poinsettia plant near cosmos flowers nearly a week after the smoke had cleared.

This monarch demonstrated it could survive the smoke that darkened the skies and ashes that covered everything in sight during the last week of October. It was a week when people wore face masks and the sun could not be seen for days. Perhaps this single butterfly represents survival methods used by other insects and animals exposed to smoke and ashes.

As for butterflies: all eggs, larvae, pupae, and adults perished in the path of the fire storms. Some islands of vegetation which were not harmed from the fire may help the reproduction of some species. In San Diego County, entomologists are confirming that isolated populations of endangered butterfly species were destroyed including those of the Laguna skipper (Pyrgus ruralis lagunae), the quino checkerspot (Occidryas editha quino), and the hermes copper (Hermelycaena hermes). The hermes copper may have harsh repercussions because redberry (Rhamnus crocea) is the only plant the larvae will eat and it takes years for the plant to mature after a fire.

The ashes that fell from the sky throughout the southwest were composed of many elements: chaparral brush, forest trees, grasses, toxins, insects, mammals, homes and people’s life possessions. Studies of fauna and flora after the fires will continue for many years until we have a better understanding of what really happened to our environment.

These fires occurred during a year when the population of monarchs during August and early September were the highest recorded in the past 15 years in Southern California, especially along the coast. They were not overwintering monarchs. They were the parents of the offspring that emerged in October and early November. The good news is that most of these newly emerged monarchs probably reached the coast and/or flew northwest before the fires began. The monarchs that traveled with the Santa Anas during the last week of October were the ones that suffered. Volunteers are presently monitoring overwintering sites and supplying information that will provide more data concerning the health and population of monarch butterflies this winter.

This satellite photograph shows the southwest movement of Santa Ana winds, represented by the trails of smoke across the Pacific Ocean, that helped cause the worst wild fires in the history of California.