Great Basin Naturalist


The cyclical phenomenon of soft and hard formation of feces in desert black-tailed jackrabbits (Lepus californicus deserticola, Mearns) was investigated. Sixty-nine blacktails were shot between 0525 hours and 1508 hours over a 4-day period. The average age was 314 days for all black-tails. The large intestine was removed and linear measurements taken. Overall length of the large intestine averaged 163.3 cm; mean length of the colon was 51.5 cm and average length of the rectum was 111.8 cm. Moisture content for soft and hard pellets averaged 79.5 percent and 74.1 percent, respectively. Protein content of soft and hard pellets averaged 45.8 percent and 14.3 percent, respectively. The black-tails began the transition from hard to soft pellets as early as 0414 hours, and nearly all had completed the reverse transition by 1508 hours. Female black-tails began both early morning and afternoon transitions significantly later than the males. Reasons for the apparent sexual partitioning are proposed.