1981] 
Mac Kay — Nest Phenologies of Pogonomyrmex 
29 
readings of thermisters permanently implanted in nests of the three 
species. The data were supplemented with readings taken during 
nest excavation, following the procedure of Rogers et al. (1972). 
Soil temperatures taken within the excavation hole (at least 20 cm 
distant from ant burrows) and within the adjacent undisturbed soil 
at the same level were not significantly different in two cases 
involving P. montanus nests (F = 0.00001ns, F = 0.13ns). Similar 
comparisons were not made in the cases of P. rugosus and P. 
subnitidus as the soils were too compacted to allow the insertion of 
a thermometer in undisturbed soil to a depth of 30 or 40 cm. 
Soil samples (160 grams) were collected at various depths and 
oven dried (60° C) to constant weight to determine water content. At 
least three replicates of soil temperature and soil moisture content 
were collected at each level. It was anticipated that these parameters 
would determine the position of the brood within the nest. I 
assumed a correlation existed between the humidity within the 
burrows and water content of the soil as well as a uniformity of the 
soil structure in the first 100 cm of the nest where most of the 
seasonal changes in the positions of the inhabitants occurred. Sandy 
soils would release more water vapor to burrows than would clay 
soils, if both had the same level of soil moisture (Marshall and 
Holmes 1979). The amount of water present within the soil changes 
continuously under field conditions (Marshall 1959), which would 
also modify the relative humidity. 
Food input into nest. 
Food input was estimated by channeling the flow of foragers and 
sampling a fraction of foragers at regular intervals to determine the 
numbers of trips made and the amount of food brought back to the 
nest. 
Twenty-eight nests of the three harvester ant species (13 P. 
montanus, 10 P. subnitidus, and 5 P. rugosus ), were surrounded by 
strips of 25 gauge sheet metal. The diameters of the enclosures were 
approximately one meter for P. montanus, 1.5 meters for P. 
subnitidus, and 2 meters for P. rugosus. The sheet metal strips were 
buried to a depth such that 10 cm of the metal were exposed. Sheet 
metal with a total width of 20 cm was sufficient. The ants could not 
normally climb over the enclosure as the sheet metal was very 
smooth. The ants would occasionally begin to climb the enclosure at 
the junction of the two ends. In such cases the area was covered with 
Tanglefoot(R). 
