1981] Mac Kay — Nest Phenologies of Pogonomyrmex 
49 
MONTHS 
Figure 9. Seasonal changes in the positions of the nest queen in three species of 
Pogonomyrmex harvester ants. 
especially short foraging period. Pogonomyrmex montanus begins 
the spring with an abrupt increase in foraging (Figure 10). The lower 
altitude species, P. rugosus, is exposed to many sunny days during 
the winter. During most of this time the nests of the high altitude 
species, P. montanus, are covered with snow. The nests of the mid 
altitude species, P. subnitidus, are covered by snow part of the time. 
In May or June foraging begins, increases throughout the summer 
and decreases again in the fall. This foraging pattern corresponds 
well with the production of workers and reproductives within the 
nest. 
Only a small portion of the population is involved in foraging. 
The mean number of foragers per day (recorded during July and 
August, the months of peak foraging) were 378 ± 73.2 (6) for P. 
montanus, 648 + 177.3 (4) forP. subnitidus, and 1427 ± 187.3 (5) for 
P. rugosus. Later excavation of the nests indicated that the 
population of foragers comprised 22.9%, 19.4%, and 18.4% of the 
total nest populations of P. montanus, P. subnitidus, and P. 
rugosus, respectively. Others have estimated that 10% of the 
population is involved in foraging in such species as P. badius 
(Golley and Gentry 1964), P. calif ornicus (Erickson 1972) and P. 
