Gashwiler, Jay S. 1979. Deer mouse reproduction and its relationship to the tree seed crop. The American Midland Naturalist. 102(1): 95-104.
Deer mice (Peromyscus maniculatus rubidus) averaged 575 males in asample of 3833 collected in the Douglas fir (Pseudotsuga menziesii) belt in western Ore-gon from 1952-1966. The percentage of mice captured in autumn and recaptured inspring was significantly greater in good (2.66 kg/ha or more) than in poor (0.45 kg/haor less) Douglas fir and western hemlock (Tsuga heterophylla) seed years. However, theautumn-spring population estimates for good and poor seed years were not sitrnificantlydifferent, but by the following autumn the good seed years had significantly greaterpopulations. There was a significantly larger number of young female (and. by infer-ence, male) deer mice in the population during the good seed years. Individuals of bothsexes were fecund each month of the year; however, yearly fecundity periods varied andthe longest were 11 months. Males were most active sexually from February -throughNovember and females from March through October. Males reached peak fecundity inMay, 1-2 months earlier than the females. The average male and female fecundity per-centage from September-March, when tree seed was most abundant, was significantlygreater for good seed years. Average yearlong fecundity for both sexes was not signifi-cantly larger in the good seed years, but for the females there was a significant difference.The percentage of pregnancies from September-March was significantly greater (eighttimes) in good years, but during April-August was only one-half of those for the poor, asignificant difference. However, on a seed year basis, the average percentage of preg-nancies was 2.9% greater for good years but was not significantly different. Averagelitter size was not significantly affected by the size of the seed fall, being 4.6 for corporalutea and 4.4 for both the embryos and placental scars. Smallest average embryo litterswere found in winter and spring and larger ones were tallied in summer and autumn.Calculated average number of litters per year was 2.9 for good seed years and 2.5 forpoor, a significant difference. The positive factors contributed variously to higher popu-lations during and/or following a good seed crop, at least by the following autumn.