Reproduction in the eastern cottontail rabbit in Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3484zm60r

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  • Reproductive characteristics of introduced eastern cottontail rabbits, Sylvilagus floridanus (J. A. Allen), were determined from 486 rabbits collected between January 1, 1968 and June 30, 1969, near Corvallis, Oregon. Sex ratios were 1:1 for all rabbits collected and for all embryos 20 days or more gestation. On the basis of weights of testes and amounts of sperm in the cauda epididymides, adult male cottontails were considered to be in breeding condition December through August, but were not considered to be in breeding condition during September and October. Much variation existed in the age at which juvenile male rabbits became sexually mature. Although some juvenile males matured sexually during their first summer of life (at about four months of age), others did not achieve breeding condition until the December or January immediately preceding their first full breeding season. On the basis of litters in utero, the 1968 breeding season was considered to extend from mid-January to mid-September. Many adult female rabbits apparently produced up to 39 young in up to nine litters during 1968. Sizes of litters produced by adult female rabbits varied with chronological sequence in 1968 and 1969. First and last litters averaged 3.75 and 4.00 young per litter respectively, whereas the remainder of the litters averaged 5.00 or more young per litter. Weather apparently affected the onset and termination of breeding. Cold, snowy weather during January and early February, 1969 appeared to delay the onset of breeding until about three weeks later than the onset of breeding in 1968. On the basis of age composition of rabbits collected January-June 1968 and 1969, it was concluded that more young rabbits were produced during August and September 1968 than during the same interval in 1969. Since the summer of 1967 was the driest on record and since the summer of 1968 was one of the wettest on record, termination of breeding in 1967 and 1968 possibly indicates the widest possible span of time in which this phenomenon might be expected to occur. Eleven (52 percent) of 21 juvenile females over 2.5 months of age were reproductively active during 1968. Three of these rabbits produced at least two litters during their first summer of life. Five juvenile female rabbits produced an average of 3.40 young per litter. Total productivity of the population was not estimated because the total contribution of young by juvenile rabbits could not be determined. However, it was concluded that total annual production of young by adult female eastern cottontail rabbits potentially was greater in western Oregon than throughout most of the natural range of the species.
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