As drought and wildfire conditions intensify throughout the west, sportsmen and wildlife biologists are concerned about the health of wildlife populations.

In much of the western United States, rainfall is 75% of normal or less for the year
(click for drought map).  According to the National Drought Mitigation Center, every state in the western half of the United States is suffering from drought impacts or is part of a drought watch area.

With continued drought, not only does the risk for wildlife increase, but degradation of habitat conditions is occurring.  In some areas, the impacts on habitat may have long term impacts on mule deer and other wildlife.

Water availability influences the distribution, reproduction, survival and relative abundance of mule deer.  In addition to needing water to sustain body functions, reduced water availability impacts populations in the following ways.

Vegetation
Seasonal rainfall influences primary production in drier environments.  Decreased rainfall can reduce the production of browse, forbs and grasses. In the case of deep- rooted browse plants, reduced water availability can impact growth for several years.  Forbs and grasses tend to rebound quicker after drought.  However, they will not produce the same amount of forage.  This means less nutrients and energy to sustain mule deer and other wildlife.

Diet, Nutrition and Growth
Mule deer nutrition is a function of plant availability, nutrient production, and feeding habits, as well as the deer's ability to digest the plants.  Mule deer are concentrate selectors, meaning they prefer to eat browse tips, forbs, and the new growth of grasses.  Precipitation and temperatures interact to influence plant production and nutrient content.  This influences what mule deer select to eat.  During years of normal rainfall, deer may feed primarily on deciduous browse shrubs.  During drought they mainly feed on evergreen and drought-resistant forages.  These plants typically have less available nutrients and energy.
Protein and energy generally are believed to be the most limiting nutrients for deer, but forage mineral content is also important.  The metabolic rate of young fawns is very high, therefore the growth of these fawns depends on the quantity and quality of the doe's milk. Marginal quality milk may be high in fat and low in protein.  Although this milk provides sufficient energy for the fawns, it lacks protein needed for growth.  Also, malnourished does likely produce less milk and fawns predisposed to early mortality.  There appears to be a correlation between precipitation/temperature index and production and survival of mule deer fawns.  In general, higher levels of rainfall correspond with improved production in herbivore populations.

Rainfall is closely linked to the energy dynamics of mule deer.  Inadequate rainfall may result in suppressed annual growth, reduced forage digestibility and availability of key forages, and increased consumption of poorer quality food by mule deer.  Relationships between weather and relative digestibility help to determine the age at which deer reach sexual maturity.  Poor nutrition as a consequence of drought can also result in stunted growth. In addition, if an animal whose growth was stunted survives the winter, it may never fully recover lost growth potential.  Ultimately, nutrition determines who will live and who will die.

Distribution and Movement and Habitat Use Patterns
Drought reduces the capability of a habitat to support wildlife.  Rainfall and snow influence the distribution and movements of mule deer.  Water is one of the most important essential nutrients, and an animal's requirements are met from free water (e.g. streams, puddles, rain, snow, dew), preformed water (contained in food), or water produced during metabolism. Drought causes animals to restrict their movements to habitats exhibiting more favorable conditions.  If these habitats are limited, deer may tend to concentrate in these areas, further contributing to habitat degradation.  Another consequence in these cases is that animals may be put at an increased risk for predation and disease.

Predation
Deer may be more vulnerable to predation in times of drought.  Rainfall may influence cover, forage, alternate prey densities, movements and distribution of the deer populations.  Limited usable habitat also concentrates predators, which means increased stress and encounters for deer.

Disease
Although, there is little documented evidence on the relationships between rainfall and disease in mule deer, outbreaks of transmittable diseases may be more common in times of drought when animals are concentrated near water sources.  This concentration of animals allows sick animals to encounter more healthy ones, which may increase the spread of disease.  In addition, insects which transmit disease may concentrate at water sources and be more likely to spread disease.

What are Managers Doing ?
    Wildlife agencies are providing water by:
         Installing Guzzlers
         Hauling water
    Agencies may restrict access to areas(i.e. close hunts)
    Agencies may increase harvest numbers

What Can Hunters Do?
    Restrict campfires
    Limit off-road travel
    Don't smoke
    Volunteer to help state wildlife agencies with water projects
    Transport adequate water into the field for themselves

Consequences to deer of poor diet and nutrition due to drought:
    Abortion of fetuses
    Low fawn birth weight
    Does have less time to prepare for winter
    Poor doe survival during winter
    Poor fawn survival - stunted growth
    Increased predation - less energy
    Reduced antler mass
    Reduced body fat
    Reduced survival