180 University of California Publications in Zoology [Vol. 27 
differences are experienced in the environmental factors of tempera- 
ture, relative humidity, evaporation ratio, and percentage of sunshine. 
At the lower altitudes halopkilus seems to be active throughout the 
year. Being terrestrial in habit, it does not have the moist environ- 
ment enjoyed by the ranas nor does it possess, like Scaphiopus, digging 
equipment which would enable it to burrow deeply into the ground 
during the dry season. Halopkilus uses any sort of available cover 
which will give it shelter against desiccation. By reason of its large 
supply of dermal poison glands it experiences relative freedom from 
enemies among carnivorous birds and mammals; at least there are 
very few reports of the finding of remains of this species in the 
stomachs of such predators. Lacking other protection than that just 
indicated, the large size of the adults seems to be an indication of the 
efficacy of this sort of protection. Food is fairly abundant in the form 
of terrestrial insects, especially nocturnally active species likely to 
escape the attention of diurnal insectivorous birds. The toad, by 
virtue of its lesser rate of metabolism associated with non-regulated 
body temperature, is probably better able to fast during times of food 
shortage than insectivorous birds or mammals under similar circum- 
stances. 
The nocturnal habit of the toad is an important factor so far as 
avoidance of desiccation is concerned. In the humid coast belt there 
is always a high degree of atmospheric humidity day and night and 
therefore little danger from desiccation. In interior localities of Cali- 
fornia where the midday temperature is high, there is almost always 
a sharp drop in temperature after sunset. This raises the relative 
humidity of the air. The colder air, being heavier, tends to sink to 
the surface of the ground so that the layer of air immediately above 
the ground has the greatest relative humidity. The toad’s activities 
are adjusted to this daily fluctuation. Rapid desiccation and death 
of the adult would be apt to follow indulgence in daytime foraging. 
At the spawning season the adults betake themselves to pools of 
water. There the moisture ratio at and just above the water surface 
is high enough to protect the animals against injury by desiccation. 
Ellis and Henderson (1915, pp. 254-255) report the finding in Colo- 
rado, of large numbers of young Bufo boreas in water about an over- 
flow pool of a hot spring at 23° C. Toads were abundant up to where 
the water was 34° C. (93° F.) and one live individual was observed 
in water at 45° C. The animals are evidently able to withstand rela- 
tively high temperatures if there is adequate moisture. 
