The diet of white-tailed and mule deer is incredibly diverse, encompassing a wide array of vegetation that shifts with the seasons and local availability. While these mammals are known to browse on woody stems and shrubs, their diet frequently includes herbaceous plants, which are non-woody, broad-leaved forbs found in both wild areas and cultivated gardens. Deer are selective feeders, meaning they seek out the easiest-to-digest, most nutrient-rich options available to maintain their body condition. Understanding their preference involves recognizing their nutritional needs and how plant chemistry influences their foraging decisions.
Deer’s Preferred Herbaceous Plants
Deer consistently select herbaceous plants known as forbs due to their high nutritional value compared to grasses or mature woody browse. These plants are generally low in fiber and packed with protein and non-structural carbohydrates, making them highly digestible. Young, succulent leaves from forbs provide the highest crude protein content, often averaging over 18% during the growing season, which is significantly higher than the minimum required for healthy growth and reproduction. Among the most favored garden herbaceous plants are young clovers, alfalfa, and tender, leafy garden herbs like basil and parsley. In the wild, highly preferred forbs include species like common ragweed, jewelweed, and horseweed.
Highly Unpalatable Herbs
Deer actively avoid many herbs that possess strong natural defenses, primarily in the form of volatile organic compounds (VOCs) and secondary metabolites. These compounds provide a pre-ingestive cue, meaning the deer can detect the unpalatability through smell before taking a bite. The most common unpalatable herbs are those with highly aromatic foliage, which is often a result of high concentrations of terpene compounds. The herbs most reliably avoided include rosemary, lavender, and many varieties of sage. These plants contain potent essential oils that are strongly scented and bitter-tasting, signaling to the deer that the plant is not a desirable food source. Other commonly resisted herbs include thyme, catnip, germander, and rue.
Factors Influencing Deer Foraging Choices
A deer’s diet is flexible, and the lists of preferred and avoided plants are not absolute. The primary environmental factor influencing this flexibility is seasonal availability, as the nutritional content of plants fluctuates throughout the year. Protein and digestibility of most vegetation peak during the spring and early summer growing period, making nearly all fresh growth more tempting. Population density is another powerful factor that can override a deer’s natural preference for palatable plants. When desirable foods are quickly depleted, deer are forced to browse on less nutritious or typically avoided species, such as strong-smelling herbs, simply to meet their daily caloric needs. Furthermore, the maturity of the plant influences its appeal; young, tender shoots are almost always more palatable than the same plant when it has become older and more fibrous.