614 THE MONTHLY BULLETIN. 



Table I. Data relative to burrows of the California Ground Squirrel. 



Type of 

 burrow 



Locality 



i 



Date (1918) 



Length of 

 burrow 

 (in feet) 



Greatest 

 depth of 

 burrow 

 (in inches) 



Average 

 diameter 

 of burrow 

 (in inches) 



Cubic 

 content 

 of burrow 

 (in cubic 



feet) 



Male 



Male 



Male 



Male 



Female 



Male 



Colonial 



Strawberry Canyon, Berkeley— 

 Strawberry Canyon, Berkeley- _ 

 Strawberry Canyon, Berkeley.. 



12 miles west of Fresno 



Strawberry Canyon, Berkeley__ 

 San Emigdio Creek, Kern Co.— 

 12 miles south, 5 miles west of 



April 3 

 April 4 

 April 4 

 May 27-28 

 April 6 

 April 27-28 



May 3 



5 

 8 

 14 



26 

 22 

 34 



138 



18 



30 

 30 

 45 

 30 



65 



■ 



48 



3£ 

 4 



41 

 5 

 4£ 

 41 



41 



1.03 



1.40 



2.40 



4.6 



4.8 



4.8 



17.8 











Average 





35.2 



38.1 



4.3 



5.2 









In illustration of the fact of variability in depth and extent of burrow 

 system with nature of soil, some actual instances as revealed by exca- 

 vation may be described. The layers of alkali hardpan in the Fresno 

 region were found to have a very decided influence on the course of the 

 burrows. In most cases where the hardpan was near the surface, the 

 burrows were found to extend through the hardpan to the soft ground 

 that is often to be found just beneath. No evidence was found to indi- 

 cate that the squirrel had dug through even thin layers of solid hardpan 

 except at points where natural cracks or openings through it occurred. 

 Slight cracks in the hardpan were sometimes enlarged, this apparently 

 having been done during wet weather, to sufficient size to enable the 

 squirrel, but not such an enemy of the squirrel as a coyote or badger, 

 to readily pass through. In following the various cracks and openings 

 through and between the strata of hardpan, the burrows were found 

 to twist about in very erratic fashion. The sudden elevation in a 

 burrow of sometimes as much as two feet was found to form a very effec- 

 tive barrier to the flow of any gas such as that of carbon bisulphid, 

 which is heavier than air; such a gas would gather into the low places 

 (see Stewart and Burd, 1918). 



The deepest burrow system uncovered was situated in an alluvial 

 talus in the foothills near San Emigdio, Kern County. The mainte- 

 nance of the great depth (from four to five and a half feet for a distance 

 of twenty feet) was clearly due to the squirrel having followed a soft 

 layer at the margin of the talus down to below the level of the four-foot 

 rock-filled surface layer. Beneath this the squirrel had progressed easily 

 through the soft soil as long as he kept beneath the rocks — which he was 

 practically forced to do (see fig. 6). 



There seems to be little cr no evidence to support the rather wide- 

 spread notion that ground squirrels burrow down until they reach 

 water. A colony burrow was unearthed in an irrigated section near 

 Bakersfield, where the water level was known to be only five or six feet 

 below the surface of the ground. No part of the burrow (see fig. 8) 

 was found to extend deeper than four feet and hence not down to the 

 water level. While ground squirrels do not absolutely require water, 

 where surface water is to be had they often go considerable distances 

 to secure it, going across the country sometimes as far as a quarter of a 

 mile. In many places squirrels are found thriving where it is known 

 that it is over 100 feet to ground water and miles to surface water. 



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