1997-06-13_REPORT - M1981302 (18)

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at the side. Quimby(1951)observed captive Z. hud onius concoct characteristic oval grass nests of various sizes, either on the surface or underground. Nests may have a soh lining in the middle of the chamber or be made of leaves, and tend to be well concealed under grass and other vegetation, or under a rotten log (Quimby 1951). Preble (1899) stated that hibernating Zapus are generally found in underground nest holes varying in depth from a few inches to 2 or 3 feet, while others have located nests in sandy slopes (Quimby 1951). D. Litters- Quimby(1951) found an average of 5.7 young per litter in Minnesota(17 litters, range 4 to 7), and a mean in New York was 4.5 (17 litters range 3 to 7) (Whitaker 1972). Krutzsch (1954) determined a mean of 4.5 by averaging embryo counts from 62 individual museum labels. Seventy-eight snap-trapped females from New York had a mean number of embryos of 5.5 (range 2 to 9) (Whitaker 1972). E. Ontogeny- Newborn young (neonates) of Z. hudsonius, based on 19 individuals, had a mean total length of 34.4, range 30 w 39 mm; mean tail length of 9.3, range 7 to 11 mm; mean hind foot length of 4.7, range 3 to 6 (Whitaker 1972). The average weight of 14 neonates from three litters was 0.8 g, with a range of 0.7 to 1.0 g (Whitaker 1972). Quimby (1951) presented extensive information concerning the growth and development of Z. hudronius, which was summarized by Whitaker (1972). Neonates had minute vibrissae, but otherwise were naked and pink, with closed eyes that appeared as dark spots. The ear pinnae were folded over the external ear openings. During the first week, the vibrissae became visible to the naked eye, the tail became bicolored, and pinnae of the ears unfolded and were tipped with black, and the claws appeared. Yellowish hairs appeared about the ninth day dorsally, and spread to include the sides about day 13. By then the vibrissae had become prominent and were about 8 mm long.The eyes were still closed, but a crack down the center was visible by about day 13, when white incisors erupted. Sparse, pale-colored hairs were visible on the belly, back of the feet and on the outer surfaces of the legs. During the third week the hair covering was completed and the external auditory meatus began to open. By this time the young were readily identifiable as jumping mice. During the fourth week the adult pelage replaced the juvenile pelage and the eyes opened. The incisors changed from white to the yellowish orange of the adult, and by day 23 all but the third molars had erupted. After the fourth week, growth of the young mice slowed considerably. By this time they were 4.6 times their length at birth, whereas at the end of the 13th week their length had increased to only 5.8 times their length at birth. Tail length had increased 10 times in the first four weeks and 12 times in the first 13 weeks. At four weeks the hind foot was 5.6 times longer than at birth and at 13 weeks it was 5.9 times longer. The young weighed about 2 to 4 g at day 10, about 4 to 8 g at day 20, about 8 to l I g at day 30, reached a minimum adult weight of about 14 to 15 g at about day 60, and weighed about 20 g by about day 90. F. Age at first parturition- Quimby (1951) presented evidence from live-trapped and snap-trapped individuals that young of early litters breed during their first summer, at an age of approximately 2 months. G. Longevity- Quimby (1951) provided definite evidence from a recapture study in Minnesota that Z. hudronlus may live to 2 or more years of age. He theorized that the proportion of a population that reaches advanced age is very small, as evidenced by the high turnover rate and instability of natural populations. FuW Slaw,Sw y Pima SCS,1a Mach ra.1993 t c