The abundance or lack of forage is an important factor, perhaps the most important, in determining local abundance of deer. Densely forested sections are not capable of supporting large deer populations because of the lack of sufficient brush, shrubbery, and succulent plants which make up the bulk of the deer’s diet. Primarily a browser, only in spring does this animal show a preference for grass, and then only for a short period. Deer have many natural enemies. It is fortunate that nature has provided for an abundant reproduction in this species. Snow is perhaps most serious of all, since a heavy snowfall may cover the food supply, and certainly hampers the movement of the animals when they must escape predatory coyotes or cougars. Late spring snows, in particular, come at a critical time. At best forage diminishes steadily during the winter months, and when this period is followed by even a short space when food is unavailable, starvation and death strikes the weaker and aged animals. Of the predatory animals, the coyote and cougar are most effective. The fox, wildcat, and bear undoubtedly take an occasional fawn, but cannot be considered dangerous to an adult deer. In view of the powers of rapid reproduction shown by deer, it is well that they have numerous natural enemies; otherwise wholesale destruction of brush lands and forest reproduction would occur as the animals reached a peak of overpopulation, followed by mass starvation. This frequently happens in many parts of the West where the natural enemies of the deer have been exterminated. Predators follow, in most instances, the line of least resistance. As a consequence, it is the weaker, the diseased, or the otherwise unfit animals that tend to be struck down first, and so the fittest survive. A reasonable balance seems to have been attained in the numbers of deer in the park. For the past several years there has been no apparent change, an estimated 600 range within park boundaries during the summer months. ROCKY MOUNTAIN MULE DEER, MULE DEER _Odocoileus hemionus hemionus_ (Rafinesque) The mule deer is similar to the preceding subspecies in general character. Perhaps the most noticeable field difference is the tail, which in the mule deer is narrow and black-tipped, above _and below_, rather than wider and dark brown or black over the entire upper surface and entirely white below as in the black-tailed. The large ears, from which this species derives its common name, are distinctive, the black-tailed deer is the smaller and darker of the two subspecies. _Specimens in park collection:_ None. The mule deer ranges over most of the Rocky Mountain region and the western United States, from the Dakotas, Nebraska, Kansas and Oklahoma westward to eastern British Columbia, Washington, Oregon and California.