Dynamics of a population of mountain cottontail rabbits in central Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/kh04dt19x

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  • Data from 186 mountain cottontail rabbits (Sylvilaus nuttallii) captured 455 times by livetrapping and from 46 rabbits collected by shooting were evaluated to determine monthly densities, survival rates, extent of movements, dispersion in relation to habitat types, and criteria for determining ages of mountain cottontails. Estimates of density computed for each month ranged from a high of 102.9 per 100 acres (40.4 ha) in August 1972 to a low of 2.7 per 100 acres (40.4 ha) in November 1973. A 74 percent decline in numbers of cottontails occurred between August 1972 to August 1973. Calculated dates of conception indicated that four litter groups of juvenile cottontails were conceived during the breeding season in 1972 while three litter groups were conceived in 1973. Onset of drought periods that began in July 1972 and June 1973 were thought to be responsible for cessation of breeding of mountain cottontails. Survival of cottontails from August 1972 to April 1973 was .18 percent.. Numbers of cottontails born in litter groups one through three that survived from birth through August 1972 were significantly different (P < 0.01) from numbers that survived from birth through August 1973. Poor survival of the third litter group, and absence of production of a fourth litter group in 1973 were thought to be responsible for lower densities of cottontails in 1973. Average distances between points of capture for mountain cottontails caught two or more times within a 30-day period ranged from 7.7 to 213.3 yards (7.0 to 195.0 in) in 1972, and from 19.7 to 171.9 yards (18 to 157. 2 in) in 1973. Analysis of the locations at which cottontails were observed during drive censuses and at which cottontails were captured by livetrapping indicated differences between diurnal and nocturnal dispersion of cottontails. These differences occurred because cottontails occurred more frequently than expected in low flats at night, and more frequently in transition areas between flats and rocky outcrops during the day. Forearms, lenses of eyes, and dentaries of 46 cottontails collected by shooting, and of 15 cottontails that died in traps or during handling between 12 July 1972 and 30 August 1973 were evaluated to determine criteria for determining ages of mountain cottontails. None of 25 cottontails less than 1 year old had ossified epiphyseal cartilages in their humeri and only 2 had ossified epiphyseal cartilages in their radii and ulnae. Seven cottontails older than 1 year had ossified cartilages in all bones of the foreleg. The relationship between ages (in days) and lens weights of mountain cottontails is expressed by: Y = -158.49 + 136.42 log₁₀X Examination of sectioned dentaries of 31 cottontails for which the approximate age was known indicated that animals that were less than 1 year old had no adhesion lines in the periosteum, while all cottontails older than 1 year had at least one adhesion line.
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