122 
Psyche 
[June 
observations were made was randomized, but always excluded those 
sides directly toward and away from the sun. The presence of the 
experimenter during a reading (an elapsed time of 10-30 sec) did 
not appear to affect the butterflies’ positions. Unless otherwise 
noted, animals were used for only one experiment and then released 
with vanishing azimuths recorded; males or females were used in a 
particular experiment. 
The butterflies’ orientation cage positions were converted to 
azimuths with a protractor. These orientation azimuths were then 
treated as a circular distribution and the following parameters ob- 
tained for each observation time (Batschelet, 1965; Greenwood and 
Durand, 1955): (1) mean orientation direction (0); (2) a grouping 
factor (r) indicating the extent to which the butterfly azimuths for 
an observation were concentrated about the 6 for that observation; 
(3) an angular deviation (AD) for 6\ and (4) the probability ( P ) of 
r occurring by chance. Computer plots were made for 6 and the 
sun azimuth values as a function of time of day. The orientation 
response of the Monarchs was considered significant when the P 
for a distribution of animals (in the orientation cages or vanishing 
azimuths) was ^ 0.05. 
Other data recorded at each reading included: (1) time of day; 
(2) temperature; (3) humidity; (4) surface wind velocity (with a 
Taylor 3105 anemometer) and direction; (5) sun azimuth and alti- 
tude computed from a Nautical Almanac and Tables of Computed 
Altitude and Azimuth for the appropriate latitude. Ambient tem- 
perature for the fall tests (10°-18°C) was lower than for summer 
(18°-32°C) experiments. When ambient temperatures fell below 
16°C, the butterflies displayed sunning behavior: turning away 
from the sun and spreading the wings in order to increase surface 
area exposed to sun and thus body temperature (Kanz, 1973; Urqu- 
hart, 1960). Sunning is often accompanied by shivering (Kammer, 
1968, 1970; Urquhart, 1960), and was only seen in fall migrants. 
Sunning Monarchs were indicated on the data sheets and in sub- 
sequent analyses, computation of 0, AD, r and P with and without 
sunning Monarchs were made. 
Results 
Field Behavior of Migrant and Non- Migrant Monarch Butterflies 
Non-migrant summer Monarchs left their overnight roosting trees 
