THE CALIFORNIA GROUND SQUIRREL. 
11 
Many ranchmen put off poisoning until the early part of the rainy 
season — in December and Januar}^. This is the least favorable 
part of the year, for the triple reason that (1) the animals are not out 
in full numbers; (2) the poisoned grain, oAving to the abundance of 
fresh green food, is less likely to be eaten: and (3) the rains waste 
the grain by burying it or washing off the poison so that the cost and 
labor of putting it out are often lost. During the dry season, on the 
contrar}', the squirrels are out in full numbers, green food is scarce, 
and any poisoned grain that may not have been eaten when first 
put out retains its effectiveness for weeks and months, so that at any 
time it may kill such squirrels as at first failed to find it, or such 
squirrels from outside as may later invade the poisoned area. 
Ground squirrels may be poisoned to advantage also during the 
breeding period, which usually falls about the end of the rainy 
season, in late ^larch and early April. At this period — extending from 
before the birth of the young until they are old enough to come out 
of the burrows — the destruction of 100 mothers is equivalent to the 
killing of 900 animals later on. 
It is popularly belicA^ed that ground squirrels can not be success- 
fully poisoned in stubble fields after harvest in summer because of 
the abundance of scattered grain. This is incorrect, for the squirrels 
habitually search for scattered grain and quickly pick up any they 
find near the runways or burrows. Some of the most successful 
experiments made by the Biological Survey have been in stubble 
fields where scattered grain was plentiful. 
Treatment of stubble fields with the starch-barley preparation at 
any time between harvest and the beginning of the rains is likely to 
prove successful. 
COST. 
In exterminating ground squirrels the most economical method is 
first to use the starch-str3^chnine preparation, and later to kiU the few 
remaining animals by using bisulphid of carbon in the burrows that 
are still occupied. 
The cost of barley coated with the starch-strychnine preparation 
varies from about $4 to $4.75 per 100 pounds, according to the price 
of the barley and the strychnine; and 100 pounds of the poisoned 
grain is sufficient to treat from 200 to 300 acres, according to the abun- 
dance of the squirrels. Assuming that 100 pounds of poisoned barley 
cost $4.50, and adding $2 for labor (1 day) and $1 for hire of saddle 
horse (in case the grain is distributed from horseback), the total cost 
of poisoning say 250 acres would be only $7.50, or 3 cents per acre. 
The animals that do not eat the poisoned grain, or for any reason 
escape, may be killed with bisulphid of carbon at the rate of H cents 
per occupied burrow. 
