1977] 
Kanz — Monarch Butterfly Orientation 
125 
with the sun visible may have been an escape reaction (see Discus- 
sion). 
Fall migrants in opaque periphery cages also displayed a sun 
orientation when the sun was visible (Fig. 3): mean | 0-sun azimuth | 
= 39°, 31% of the readings showing significant Monarch concen- 
trations about the mean orientation direction (Table I). Low am- 
bient temperatures during fall tests (10°-18°C) compared to sum- 
mer tests (18°-32°C) might be one reason for the difference in 
sun-orienting response between the two populations. However, 
the data suggest that caged fall migrants sun-orient when the sun 
is their sole orientation cue. Sun orientation would result in fall 
migrants moving south, the direction Monarch butterflies take 
during their fall migration. A distinction can be seen between the 
sun orientation of fall migrants and summer non-migrants in 
opaque periphery cages: the mean 1 0-sun azimuth | value for fall mi- 
grants was not as consistent throughout the day as it was for non- 
migrants. Caged fall migrants showed a mean orientation direction 
closer to the sun’s azimuth (mean 1 0-sun azimuth | = 31°) from 1000 
to 1400 hrs (EST) than before or after this time period (mean 1 0-sun 
azimuth | = 44° and 52°, respectively). The 1000-1400 hrs time 
period corresponds to the migratory period of fall migrants (Brower, 
personal communication; Kanz, 1973; Urquhart, personal commu- 
nication; Kanz, 1973; Urquhart, personal communication). The 
sun-orienting response of non-migrants on the other hand, was 
consistent, or even improved, throughout the course of the day 
(30°, 27°, and 12°, respectively for prior to 1000 hrs, 1000-1400 
hrs and after 1400 hrs). This suggests that there is more to the sun 
orientation of fall migrants than a sun-orienting escape response. 
The wider divergence of 0’s from the sun’s azimuth in the fall 
tests cannot wholly be ascribed to cooler autumn temperatures in 
the morning and late afternoon hours. Two fall experiments, in- 
cluding that illustrated in Fig. 3, were conducted when ambient 
temperatures ranged from 13° to 16° C. This temperature range 
was less than or equal to that recorded for the time period 1000- 
1400 hrs for all but two of the remaining fifteen tests of this series 
(i.e., fall migrants in opaque periphery cages with the sun visible). 
Caged migrants from these two tests still showed a mean orienta- 
tion closer to that of the sun’s azimuth during the observed 1000- 
1400 hr migratory period. The orientation of caged fall migrants 
was random on overcast days (Table I). 
