1977] 
Kanz — Monarch Butterfly Orientation 
135 
Discussion 
The experiments reported here were designed to delineate the 
role of the sun in Monarch orientation. The sun was selected as 
the most probable cue in the orientation of Monarch butterflies 
for several reasons: (1) the Monarch is a diurnal animal and the 
sun is a prominent cue in its environment; (2) a positive phototaxis 
has been reported in a number of Lepidoptera (Brandt, 1934; Col- 
lins, 1935; Dolley, 1916; Jander, 1963; and Kelsheimer, 1935); (3) 
the sun has been shown to be important in the orientation of a 
number of animals (Hasler, 1967; Schmidt-Koenig, 1961; Taylor 
and Ferguson, 1969; and von Frisch, 1967), including migrating 
European butterflies (Baker, 1968a,b). 
Non-migrant Monarchs (laboratory-reared) demonstrated a sun 
orientation when tested in an opaque periphery orientation cage 
with the sun visible. This response was termed an escape response. 
A sun-orienting escape response for Monarch butterflies is appro- 
priate for three reasons. First, the most prominent orientation cue 
available to Monarchs in opaque periphery cages on a clear day is 
the sun. Second, when fast escape flight is warranted, Monarch 
escape would be linear and, therefore, fastest when the animals use 
a constant cue, such as the sun, for orientation. Third, when fol- 
lowed by a predator, a sunward escape response would put the sun 
in the predator’s line of sight thus making it more difficult for the 
Monarch to be detected. 
The orientation of summer non-migrants was random with both 
terrestrial and celestial cues present. If Monarchs were attempting 
to escape, the sun did not appear to be their orientation cue. This 
random orientation was believed to be indicative of the orientation 
of uncaged, non-migrant, Monarchs during the summer, since sum- 
mer animals are known to wander randomly (Urquhart, 1960). 
Verheijen (1958) has criticized phototaxis experiments on the basis 
that the test situations eliminated scattered and reflected light, 
therefore making the illumination of the animal’s environment 
unnatural. Illumination conditions (as well as conditions in general) 
during Monarch testing in transparent periphery cages, more closely 
approximated a natural field situation for Monarchs than the con- 
ditions encountered with opaque periphery cages. Thus the re- 
sponses of transparent periphery cage butterflies might be expected 
