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Psyche 
[June 
to more accurately represent Monarch orientation. 
It has been assumed that Lepidoptera displaying positive photo- 
taxis (Johnson, 1969) were flying directly toward a light source. 
Hsiao (1973), however, has found that the corn earworm moth, 
Heliothis zea, flies toward a dark band surrounding the light source. 
Hsiao suggested that this Mach band explanation (Graham, 1966) 
could explain the attraction of night-flying moths to ultraviolet 
light sources: moths seek darkness characteristic of their diurnal 
behavior, although they appear attracted to ultraviolet light. Hsiao’s 
results raise the possibility that sun orientation of Monarch butter- 
flies is an orientation to either (1) a Mach band surrounding the 
sun, or (2) a Mach band perceived between the sun and the darker 
horizon. However, the Monarch is a diurnal butterfly, not a noc- 
turnal moth, and butterflies generally seek sun-light areas instead 
of shaded areas (Klots, 1961). 
Data from experiments with caged butterflies might represent 
landing orientation. However, when observations were made (at 
times ranging from 1-15 min after cage rotation), few, if any, 
Monarchs were in flight or landing. In general, the butterflies were 
either stationary or walking. 
The location and shape of the horizon in opaque vs transparent 
periphery cages could also have affected Monarch orientation. 
Orientation to mountain tops by many Coccinellidae (Hagen, 1962), 
and to tree tops by the Scolytid beetle, Conophthorus coniperda 
(Henson, 1966), is presumably based on horizon-orientation. Never- 
theless, sun orientation by fall migrant Monarchs persisted in spite 
of horizon differences between opaque and transparent periphery 
orientation cages. It seems unlikely, therefore, that the cage ori- 
entation of these insects was significantly affected by horizon dif- 
ferences. The orientation displayed by summer non-migrants was 
different in the two types of cages. This difference might reflect an 
horizon influence, but other factors, such as the presence or absence 
of terrestrial cues, are equally likely. 
When the sun was visible, fall migrant Monarchs oriented to the 
sun’s azimuth regardless of the type of orientation cage. In con- 
trast, non-migrant orientation was sunward only in opaque periph- 
ery cages. One explanation for this difference in orientation re- 
sponse could be that a sun-orienting escape response is stronger in 
fall migrants than in summer non-migrants. Tables I and II show 
that the sun orientation of fall migrants (opaque or transparent 
