Painted Lady (Vanessa cardui) migration 2009

Vanessa cardui

Vanessa cardui

UPDATE: May 1, 2009

The northward migration finally seems to have ended in the past week, albeit with a minor reversed direction again at the very end. So few animals were in migratory mode by then that one cannot confidently separate the phenomenon from directional randomness. Dozens of very battered animals are still hanging around, nectaring and laying eggs, and larvae are becoming easy to find, especially on thistles.

Painted Lady

Painted Lady

This morning, May 1, as I walked in to work at 0740, I disturbed a Painted Lady that had apparently spent the night on the sidewalk in College Park, Davis. It was very large, brightly colored, and obviously very fresh and it flew off to the NNW. The direction may or may not be significant, but its presence is: it presumably enclosed yesterday and is the herald of the locally-bred next wave. From now until early June we are likely to see batches of these large, bright PLs eclose, feed for a few days, and depart for the north. Unlike the desert-born ones, they do have to feed. Historically this generation has swarmed the flowers of Linden (Tilia), shrubs of the Rosaceous genus Cotoneaster, and Pride-of-Madeira (Echium fastuosum). The very long migration period in March-April augurs unsynchronized emergences for the next several weeks. Records, observations and pictures are welcome!

UPDATE: April 20, 2009

Painted Ladies continued to migrate through the Central Valley at relatively low and inconspicuous densities, with day-to-day variations in numbers. On the afternoon of April 12 a concerted reverse flow began toward the SSW at Davis and toward the W near Dixon. This became nearly a due N>S flow for the next 3 days, though at all times a few individuals were seen moving in the normal SE>NW direction. Such reversed flows have occurred for a few days in prior migrations, and are not understood. (They are cited in my book on p. 196.) On April 14 a severe cold N-wind event in the Central Valley limited butterfly activity. From the 15th through the 17th directionality became confused and at times nearly random. From the 18th forward the flow was almost entirely SE>NW again, with many individuals dropping out to feed and reproduce and wing condition becoming very worn. There were a few scattered reports of S-ward movement near the coast, but not on any large scale as was true inland. On April 18 Ron Jurek reported two separate flows at Auburn, Placer County (1200’), one from the S>N/NNW and another from the E>W/WNW simultaneously, suggesting that these had been funneled by the topography. This could be purely local, or it could reflect two major streams with different orientations—wish we had more records like this! Numbers near the coast remained generally low, with occasional brief surges. Two Sierran trips – most recently April 19 --revealed a steady but thin continuing movement toward the NW, very sparse at the highest elevations. Intermittent surges continued to be observed at Reno, with one report from the Sweetwater Mountains. One newly-emerged individual was observed last week in the Sacramento area, presumably from an early-season reproductive event. As of this writing (3 PM, April 20) individuals are moving through the UCD campus at a rate of 1 every 3-4 minutes in my visual field, with at least 90% of them going N to NW and most of the rest going S to SW, with one individual seen headed due E. All of these are seemingly in migratory mode and not stopping to nectar or oviposit. How long can they keep coming?! Your observations continue to be welcome.

UPDATE: April 10, 2009

Numbers of migrating Painted Ladies continue to wane west of the Sierra Nevada, but a few are still in migratory mode. On April 4, 306 were counted in Rancho Cordova, Sacramento County, about 2/3 in migratory mode--~1.7/minute. Numbers went up late in the day and a minor surge was noted in Yolo County in very late afternoon. On April 8, 44 were seen in North Sacramento, also Sac. Co., about half of them migrating, at a rate of about 1 every 3 minutes. One very fresh individual was also seen, apparently newly-enclosed locally and presumably the offspring of a very early migrant, probably in February or very early March. Scattered migrating individuals continue to pass through Davis, even under cloudy and cool conditions, but there has been no major activity since the 4th.

I went over Donner Summit again on April 5 and encountered very scattered individuals in the western foothills along I-80 and none at higher elevations. There were 3 migrating toward the NW at Sierraville, Sierra Co. The next day, April 6, I received multiple reports of significant numbers heading N to NW through Reno, NV and on nearby Peavine Peak. On April 7 they were reported from Tahoe City, Northstar, Kings Beach, and the Sugar Bowl ski resort at Donner, all in good numbers. It thus appears that there is in fact an E-slope migration this year, but it comes just as the very prolonged W-slope one is ending. I apparently missed the front by one day! They seem undeterred by the nasty turn in the weather.

Stay tuned.

UPDATE: April 3, 2009

At midweek numbers of incoming Painted Ladies tailed off across the Central Valley and Bay Area, and large numbers of individuals began dropping out of the migration, nectaring at flowers, setting up male territories, engaging in courtship, and laying eggs. These activities coincide with the depletion of the migratory fat reserve. Male territories typically are occupied in late afternoon in sites open to the sun (facing W to SW) and with some kind of vertical backdrop. Mateable females lure males up into the trees, where actual copulation takes place-- typically out of sight. Very few people have seen Painted Ladies mating! The pair often remains in copula through the night, and egg-laying begins the next morning. We are posting a photo of an actual copulation, kindly provided by one of our on-line correspondents who has been tracking the migration in the South Bay. Eggs are laid one at a time on thistles, borages, mallows and less frequently on lupines, plantains, cocklebur, sunflower and a variety of other herbaceous plants.

Painted Ladies copulating

Painted Ladies copulating

A new and intense surge of migrants hit the I-80 corridor in the Central Valley in early afternoon on Thursday, reaching densities comparable to those observed on March 25. This surge was also reported from the Sierran foothills but we have not heard of it near the coast. Unlike the previous batch, these butterflies were in single-minded migratory mode and were not getting diverted by either food or sex. We still have no reports of mass movements in the northern Sierra or western Great Basin. There were no prior indicators from our correspondents to the south that the April 2 surge was coming, and we do not know where it came from except that the leading edge may have been in the Auburn (Placer Co.) area a day before it showed up here. Does anybody out there know?

UPDATE: March 30, 2009

The main body of the migration shifted coastwise beginning Friday. While numbers east of Davis dropped to near “background” levels, another surge passed through Davis and westward late Friday and on into Saturday. At the same time, we received many emails from Santa Barbara to the North Bay counties, indicating a major NNW-ward movement which is still continuing as of midday Monday. I did a recon across the Sierra Nevada Saturday in and N of the I-80 corridor (N to Sierra County) and saw only a handful on the entire trip, including 2 going due N at Sierraville and 1 on Hwy.89 between Truckee and Sagehen Creek. There have been no reports thus far of any mass movement up the E slope. A dry cold front dropped temperatures 20 degrees F there on Sunday. The same front induced strong N to NW winds in the Sacramento Valley, with gusts to 40+ MPH on the W side of the Valley where a “barrier jet” developed. Only a handful of butterflies attempted to buck these winds, so as of now it’s impossible to tell if the migration is spent inland. This migration may actually be comparable in density to the 2005 one near the coast, if not even better. When things settle down, we will try to synthesize all the information we have available and publish it. Keep the news coming!

Original Post: March 26, 2009

MOMMY, I SAW A BUF’WY! (Exclamation from a toddler in a park in Rancho Cordova, Sacramento County, March 25, 2009)

Another Painted Lady (Vanessa cardui) migration is occurring in north-central California. Painted Ladies showed up very early in the region, in late January, and there are hints of overwintering and breeding somewhere in south-central or southern California somewhere north of the usual desert breeding grounds along the Mexican border, because these animals were in good condition and did not appear to have migrated long distances. They also did not show the usual color-and-pattern signs of having been generated in the desert, but they were not produced locally in the Davis-Sacramento region and were seemingly confined to the west side of the Valley.

Painted Lady migration 2009

Painted Lady migration 2009

The first wave from the desert showed up in mid-March. We received reports of significant numbers migrating through the Sierra at Mammoth Lakes as of March 15. What is assumed to be this front reached the Davis-Sacramento area on March 17 and was also recorded at Atascadero on March 19. Numbers dropped off at Mammoth Lakes but another wave passed through there (despite iffy weather) on the 21st. A front passed through the vicinity of Merced and Santa Nella on the 21st also—perhaps having crossed the Sierra farther south—and a few were seen at Pollock Pines the same day. A major front, probably the Mammoth one, passed Placerville on the 22nd and hit the Sacramento-Davis area beginning near dusk on the 23rd, increasing through the 24th and 25th. Presumably the same front hit San Jose on the 24th. This seems too long an interval for it to have been the one at Santa Nella on the 21st. Densities on the Valley floor were unimpressive on the 24th but much higher on the 25th, when 1-minute counts of butterflies crossing an imaginary line to the horizon perpendicular to their path in open grassland in eastern Sacramento County peaked at 61, or 1/second. This is roughly 1/3 of the peak recorded during the perhaps-record March migration in 2005. There have been no reports of densities high enough to impact traffic flow, as happened in 2005.

Because several streams of migrants are clearly involved and we have gotten no reports from the Inyo-Kern area, which is typically a major Painted Lady highway, we cannot be sure of the timeline for all of these movements. These butterflies are powered by yellow fat carried over from the caterpillar stage, and fly like “bats out of Hell” from SE to NW a few feet off the ground, not stopping for food or sex until their fat reserves become depleted. Only a tiny fraction of the butterflies seen this week have been seen feeding, and only one female has been seen laying eggs.

This report will be updated periodically as new information comes in. See the Painted Lady page at or pages 48-51 and 195-200 in Field Guide to Butterflies of the San Francisco Bay and Sacramento Valley Regions (University of California Press, 2007). New reports or queries can be emailed to me at Videos of the migration for posting on our Web site are welcome and will be fully credited.

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