. Bulletin. Science; Natural history; Natural history. 158 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. Fig. 2. Bishop emergence site, showing migration flight paths taken during mass exodus of newly- emerged Vanessa cardui adults. Cross-hatching = area of high-density hostplant (Amsinckia), black arrows = June 5-10, 1991 observations, light arrows = May 16-19, 1986 observations, GN = geo- graphic north, MN = magnetic north. Bishop Adults At the Amsinckia site west of Bishop on 28-31 May, only one to three migrating adults were observed each day. During 5-11 June the vast majority of the pupae eme
. Bulletin. Science; Natural history; Natural history. 158 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. Fig. 2. Bishop emergence site, showing migration flight paths taken during mass exodus of newly- emerged Vanessa cardui adults. Cross-hatching = area of high-density hostplant (Amsinckia), black arrows = June 5-10, 1991 observations, light arrows = May 16-19, 1986 observations, GN = geo- graphic north, MN = magnetic north. Bishop Adults At the Amsinckia site west of Bishop on 28-31 May, only one to three migrating adults were observed each day. During 5-11 June the vast majority of the pupae emerged and the adults migrated, with a maximum of 224-342/5 min/15 m on 9-10 June. These migrations radiated in almost all directions (except east) from the population center (see Figure 2), primarily during 7:00-10:00 AM, sometimes with a few continuing until 1:00 PM (5 June). Unlike "normal" migrators, these usually flew slowly, were easily distracted by other V. cardui flying nearby and flowers, and ceased migrating when the heat of the day built up, although lighter migration flights occurred in the late afternoon. The numbers considerably de- clined on 11 June during the hottest temperatures of the year (to then), when most migrators had already departed and few new ones were emerging to replace them. In the late morning and during the afternoon, newly emerged adults congregated at flowers and in shrubs of Chrysothamnus (Asteraceae), Atriplex, and on the twigs of dead shrubs. Very small shrubs had almost none. These freshly emerged adults apparently waited until the following morning before migrating due to high midday and afternoon temperatures. Several freshly emerged (limp) adults displayed a strong tendency to climb up on vegetation. One of these nervously snapped its wings open and closed at each movement made by a nearby ant on two occasions. A passing car on 7 June at 11:30 AM caused huge numbers of freshly emerged individuals to rise into the air from the r
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