production and recruitment, dispersal of females and yearling 

 males resulting from parturition territoriality fills in more 

 and more sub-optimal habitat. When environmental conditions 

 reverse (drought and severe winters), those dispersers that 

 established a migratory tradition are able to maintain 

 relatively better living conditions by migrating back to core 

 areas during autumn and winter, after productive females 

 become more tolerant of other deer. Females living in 

 marginal habitat that did not establish a migratory tradition 

 are subject to poorer forage quantity and quality during late 

 summer and autumn as well as deeper snow and colder effective 

 temperatures during winter. Those females and their fawns are 

 more vulnerable to mortality from all sources. 



Because of this, fawn production and deer mortality are 

 in a sense "density-dependent", although not in the classical 

 manner. At higher densities, more deer live in "marginal" 

 habitat and are subject to higher rates of mortality. 

 Increased mortality results not because of a measurable 

 reduction in the food supply owing to intra-specif ic 

 competition, but because more deer are occupying habitats in 

 which they are vulnerable to drought and severe winters. 

 During the most extreme conditions, females in core habitats 

 may not recruit fawns, but resources within their home range 

 are adequate for survival of non-productive adults. During 

 extreme environmental conditions, some marginal habitats may 

 not provide even for the survival of adults. Dusek et al . 

 (1989) expressed similar views regarding population regulation 

 in white-tailed deer on the Lower Yellowstone River of 

 Montana. They indicated that socially influenced resource 

 partitioning relegated younger females to sub-optimal habitat, 

 resulting in lower productivity. The importance of habitat 

 patchiness and a combination of optimal and suboptimal habitat 

 to population dynamics has also been noted for snowshoe hares 

 (Lepus americanus) (Wolff 1980) and California voles (Microtus 

 californicus) (Ostfeld and Klosterman 1986). 



The weather and climate of an area has both stable, 

 predictable characteristics and variable, unpredictable 

 characteristics. Winter months are predictably colder than 

 other months, vegetation is dormant, and snow cover is often 

 present. Deer adapt to this predictability by undergoing 

 winter torpor (Silver et al . 1969) and practicing energy 

 conservation by establishing home ranges that include southl- 

 and north-facing slopes that provide reduced snow depth and 

 relatively warm microsites during the day and at night, 

 respectively. Vegetation-forage conditions are predictably the 

 most favorable each year during late May and June, even during 

 dry years. The predictability of the general weather pattern 

 results in late November breeding and June parturition dates, 

 when the combination of sufficient time for recovery from 

 winter, succulent forage during lactation, and adequate time 



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