1976] 
Alcock — Populations of Centris pallida 
125 
the ground when searching for digging sites. It was impossible 
to determine the color combination of flying males and it was 
difficult to capture them as well. Often a marked male was seen 
close up (while digging) or was captured only once or twice during 
the morning flight period over emergence areas. Nevertheless, a 
considerable number of males were seen frequently in the same 
general area over a period of days. The positions of twelve of these 
males were plotted on maps of the study sites for periods of 2-9 
days of observation; these individuals covered areas roughly 8-46 
m 2 (x= 18 m 2 ; s.d. = 12.5 m 2 ). This seemed to be the typical pat- 
tern although we have records of eight males that were seen at 
two separate centers of emergence about 25-35 m apart. Three 
additional males moved back and forth several times between 
locations that were separated by at least 80 m. Finally, at least 
some males moved permanently from one emergence area to 
another distant one, with five males found patrolling sites 60-100 m 
from the point of their capture and two others patrolling about 
200 m from where they were taken initially. 
To repeat, the very large majority of males that were recaptured 
were never found outside an area of about 50 m 2 around the point 
of original capture. Those males known to patrol two searching 
areas and those known to have moved large distances make up a 
very small minority of the total recaptured males. Thus although 
the activity in a large emergence area appears chaotic and random, 
in reality the region is divided into a large number of broadly over- 
lapping home ranges with individual males systematically patrol- 
ling small portions of the total available searching area. 
The behavior of hoverers 
At Site 1 males were found hovering a few cm above the ground 
centered in depressions or openings surrounded by short desert 
shrubs under a meter in height, as well as close to the ground 
around the edges of mesquite trees, and at all altitudes in flower- 
ing palo verde trees. Those males hovering at low aerial stations 
in and around emergence sites were present primarily during the 
peak hours for emerging females (0830-1100). Males hovering 
at or near flowering trees were present throughout the day al- 
though there may be a slight decline after the period of female 
emergence (Fig. 2). 
Hovering males continually leave their aerial station to pursue 
passing insects, usually for a few seconds only, before returning 
