Summary: Wild Fires 2003 in Southern California
We will never know the true story of the influence of the Southern California wild fires on migrating monarchs in late October. We have evidence of survivors living through the days of dark, smoky skies (based on tagging reports), but we do not know how many perished when flying with the Santa Ana winds during the worst fire storms in the history of California.
In late November and early December, Monarch Program associates Bill Howell and David Marriott visited 59 coastal overwintering sites south of Santa Barbara County into Baja California, Mexico and toured 200 miles of fire devastated areas in San Diego County. Early reports from Howell and Marriott reflect sad news from San Diego. In some areas, or as far as the eye could see, there was nothing but the remnants of a nuclear bombing. Scattered throughout the mountains and valleys were small pockets of native vegetation that were not burned. Each of these areas may become an oasis for animals to help repopulate. Some animal species, including the Thorne’s hairstreak butterfly (Mitoura thornei), may now be extinct. It will take years to assess what type of impact the fires had on plant and animal colonies.
The fire storms may have affected large numbers of migrant monarchs in late October because overwintering sites south of Santa Monica to the Mexican border had fewer monarchs than last year — the lowest year recorded for this area. Overwintering sites north of Los Angeles County to Santa Cruz County are reporting larger population numbers than last season. The end of a four year drought is probably helping the increased population.
The red gum eucalyptus trees are making a comeback from the lerp psyllid infestation. The leaves are green and the mid-range foliage is returning, however the monarchs are not returning in the Southwest. All conditions were right: high numbers of caterpillars on milkweed reported in September, end of a four year drought, healthy eucalyptus groves, and no monarchs? Before the drought, we had at least 26,000 monarchs spending the winter in San Diego County. This season we counted 58.
Based on population figures from other counties this season, and past records, the Southwest should have had a population 5 – 10 times as high as recorded. Could the gap have been the result of monarchs that were affected by the fires? A few more years of monitoring overwintering sites may shed light on what impact the fires had on migrating monarchs this season. Obviously some were lost, but we do not have clear evidence as we do with mountain lions, deer, and other large animals.
Below is a list of Thanksgiving Monarch Counts south of Santa Barbara since 1997. The “number of sites checked” should be balanced with the number of monarchs sighted from year to year to obtain an average population number. For example, nearly twice as many sites were checked in San Diego this season (see population number) as compared to last season, thus the total population last year may have been twice the number listed for that season. All population numbers are not exact. They are an accumulation of numbers provided by volunteers estimating populations at overwintering sites during the Annual Monarch Thanksgiving Count along the west coast in late November and early December.
