. The Canadian field-naturalist. The Canadian Field-Naturalist Vol. 105 Table 4. Reproductive data on the Northern Grass- hopper Mouse in southwestern Manitoba. Number and Length Number of of Embryos Placental Date (mm) Scars 18 April 4 8 June 4 5 5- 7 17 3-10 29 July 6 11 August 4 12 4 13 3- 8 5- 7 2-13 14 5- 4 4-14 5-18 4(n= 10) Average (n = 3) Range 2-5 4-6 Remarkably little is known about the reproduc- tive biology of the Northern Grasshopper Mouse (Banfield 1974). The gestation period has been found to be as short as 26 days and up to 47 days if the female was lactating. Over much of
. The Canadian field-naturalist. The Canadian Field-Naturalist Vol. 105 Table 4. Reproductive data on the Northern Grass- hopper Mouse in southwestern Manitoba. Number and Length Number of of Embryos Placental Date (mm) Scars 18 April 4 8 June 4 5 5- 7 17 3-10 29 July 6 11 August 4 12 4 13 3- 8 5- 7 2-13 14 5- 4 4-14 5-18 4(n= 10) Average (n = 3) Range 2-5 4-6 Remarkably little is known about the reproduc- tive biology of the Northern Grasshopper Mouse (Banfield 1974). The gestation period has been found to be as short as 26 days and up to 47 days if the female was lactating. Over much of the range mean litter size was reported to be 4 (1-6), with several litters produced from April to early October (Smith et al. 1975). Both sexes have been found to be capable of breeding at four months of age in captivity, but wild mice did not appear to become sexually active until their second year (Jones et al. 1983). Soper (1964) noted two litters of 2 to 5 young per year in Alberta. In the present study (Table 4) ten litters averaged (2-5) embryos and placental scars (4-6), with pregnancies from IK April to 14 August. Juveniles were caught throughout June, July, and August (indicating at least two annual litters) and none was in breeding condition. Western Ji mping Moi si Zapusprinceps I he Western Jumping Mouse (Figure 7) was undetected by Seton (1909) in Manitoba and was Ins! recorded by Criddle(1929) al Aweme (north ol Irccsbank) where it was listed as rare. I" ( riddle's series ol 17 specimens (collected from 1912 to 1936) al Aweme and one other from Soui is. were added foui specimens from Pembina Rivei (ninth ol Mowbray) and Pelican lake by Sopei (1961) Mi* National Museum ol Natural Sciences (now ( anadian Museum ol Nat me) has lix from Shoal I ake (the northern record foi the province) and two from Oak lake During the present studs we captured 105 specimens al 28 lot alities, extending the range marginally to l km n ( romer; 4 km S, 4 km 1 Virden; k
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