Deer are the most common large wild mammals that most of us see. The only areas that lack deer entirely are within the city limits of our biggest cities. Any of us who live out in the countryside are likely to have them in our garden, not necessarily a preferred situation.
Two species inhabit the Pacific Northwest, Mule (Odocoileus hemionus) and White-tailed (O. virginianus). Mule occur everywhere, White-tailed mostly in forested habitats east of the Cascades in Washington and northeast Oregon, with a small population along the Lower Columbia River. The latter population is usually listed as a separate subspecies and is of conservation concern.
There are two very distinctive subspecies of Mule in the Northwest, the true Mule Deer (O. h. hemionus) and the Columbian black-tailed Deer (O. h. columbianus). Black-tails are smaller and darker than "muleys" and live in the wetter and more heavily forested areas west of the Cascades crest. They are typically seen at forest edge, although where not harassed they feed well out in open meadows. Mule Deer are common in open woodland and grassland east of the Cascades, drier habitats where their pale coat is more appropriate.
The three types can be distinguished by several characteristics. White-tailed have a long tail, brown above and white below, that is elevated like a flag when one is disturbed and goes bounding away. Mule and Black-tailed keep their smaller tails down. In both, the tail is white below, but in Black-tailed, as the name implies, it is black above, while Mule have the tail base entirely white. Intermediates between these two types are fairly common near the Cascade crests, where they meet and interbreed freely.
Males are larger than females and have antlers in fall and early winter. The antlers serve them to impress other males and keep them away from any female they are protecting as a potential mate. The antlers of Mule and Black-tailed branch dichotomously, with even-length branches, while those of White-tailed have a main branch ("tine") with smaller tines branching off from it.
Deer are generalized herbivores, nibbling leaves from a great variety of shrubs, trees and herbaceous plants, including grasses. A listing of their diets would include all of the common plants in their range except those that are protected by chemicals or serious thorns. Because they are generalists, not many plants in your yard are immune to their incisors.
Most mating takes places in late fall and births in early summer. One young is usually produced, but twins are also common, especially in older female Mule and Black-tailed.
White-tailed Deer have increased and expanded their range, while Mule Deer have declined In Washington state in recent years. As in eastern North America, human land use —both opening up forests and planting trees—seems to favor White-tailed, while our activities in general are less favorable for Mule Deer. Black-tailed Deer are holding their own, probably because their habits are more like those of White-tailed. They are protected in many areas just because they live in close proximity to human neighborhoods.