 Females journey up to several kilometres in July to November to reach nesting areas of dry , sandy coast . Nest digging is a tiring and elaborate task which may take the female several hours a day over many days to complete . It is carried out blindly using only the hind legs to dig a 30 cm ( 12 in ) -deep cylindrical hole , in which the tortoise then lays up to 16 spherical , hard @-@ shelled eggs ranging from 82 to 157 grams ( 2 @.@ 9 to 5 @.@ 5 oz ) in mass , and the size of a billiard ball . Some observations suggest that the average clutch size for domed populations ( 9 @.@ 6 per clutch for C. n. porteri on Santa Cruz ) is larger than that of saddlebacks ( 4 @.@ 6 per clutch for C. n. duncanensis on Pinzón ) . The female makes a muddy plug for the nest hole out of soil mixed with urine , seals the nest by pressing down firmly with her plastron , and leaves them to be incubated by the sun . Females may lay one to four clutches per season . Temperature plays a role in the sex of the hatchlings , with lower @-@ temperature nests producing more males and higher @-@ temperature nests producing more females . This is related closely to incubation time , since clutches laid early incubate during the cool season and have longer incubation periods ( producing more males ) , while eggs laid later incubate for a shorter period in the hot season ( producing more females ) . 
