Food Requirements:
Specific Seasonal Deer Diets
Specific dietary items consumed by deer are presented in a season-by-season manner. Pictures and descriptions of important food plants are presented in Appendix C. When important food items could not be identified beyond the "complex" level, all plant species occurring on the NFWU in the appropriate complex are presented in Appendix C. Species that were used but did not meet the "important" criterion are listed in Appendix B.

Spring
Spring temperatures in much of the Cross Timbers can be erratic. Depending on the year, early spring may bring relatively warm days with cool nights, thus encouraging an early green-up. Often however, early spring more closely resembles winter with occasional freezes occurring as late as mid April, especially in the more northern areas of the region. Latter stages of spring most often resemble summer. Days are generally hot, but nighttime lows are usually in the 60’s. Spring is the season in which the Cross Timbers receives the largest percentage of its average annual rainfall. May is typically the wettest month.

Relatively speaking, spring is typically a "time of plenty" from a deer food perspective. Early spring is often marked by an abundance of cool season grasses and cool season forbs and the emergence of many warm season forbs.

A total of 20 plant species and plant complexes were identified in the spring diet of deer that satisfied the important criterion (Table 1). These items accounted for 95% of the spring diet. The most preferred spring food item was Carolina snail-seed. Not only was it most preferred, it also comprised more than 16% of the spring diets during both study years. Sweet clovers, wild beans, clammy chickweed, and Carolina cranesbill followed in the preference rankings. Also noteworthy are osage orange, ragweeds, and the sumacs-poison ivy complex which made substantial contributions to the spring diet (greater than 10% of the diet in at least one spring collection period). Their intermediate preference rankings relative to the food items previously mentioned were more attributable to their high relative availability rather than a low ranking of use.

Another food item that warrants mentioning is winged elm. While winged elm met the criterion for being an important dietary item during the spring (and it is noteworthy that this is the only season in which it did make the list), it is important to point out that it was a relatively abundant browse species on the NFWU. The percentage of winged elm in the diets was less than that of its availability, indicating it was not selected for. It is reasonable to assume that winged elm has pretty low importance in good condition Cross Timbers deer habitat. Its importance could increase however, as habitat conditions worsen and deer are forced to use it.

Summer
Summers in the Cross Timbers are usually very hot. Average high temperatures are usually in the mid to high 90’s for many parts of the region during July and August, which are the hottest months. It is common for temperatures to reach and often exceed 100 degrees. Rainfall for the area averages roughly 2-4 inches throughout the summer months. These figures may be misleading however, because summer droughts are common. Almost every summer, portions of the region go without rainfall for an extended period of time. The rains often come in the form of isolated afternoon thundershowers, creating a patchwork of areas receiving precipitation and those which do not. Often it seems that a boom or bust situation exists throughout the summer, with some areas receiving the majority of rainfall. August tends to be the driest summer month due to the cumulative effects of prolonged high temperatures and high evaporation rates.

Summer has the potential to accentuate extremes relative to deer diets. At the onset of summer, foods are generally relatively abundant. The normally high precipitation during May and June facilitates adequate food production at this time. As summer progresses however, drought stress usually begins taking its toll on plant growth and condition; this effect usually peaks during late August. In spite of this droughty scenario, the late summer sampling periods consistently provided the greatest plant biomass. While much of the vegetation was probably rank and relatively unpalatable, deer evidently have evolved and adapted to cope with the situation by selecting specific plant parts that are palatable and nutritious.

Roughly 85% of the summer diet consisted of the 24 plant species or plant complexes judged to be important summer food items (Table 2). Yerba de tajo, which was very limited in availability, received the highest preference ranking, followed by the three-seeded mercuries. Tick clovers and wild beans, both legumes, ranked third and fourth, respectively. Surprisingly, the crotons or doveweeds ranked fifth in summer diet preference. This group was identified only to the complex level, but based on the limited species specific microhistological information and casual observation of plants in the field, woolly croton was probably not a big contributor to the observed use.

Fall
Fall in the Cross Timbers is generally a pleasant time of year. Daytime temperatures begin cooling off in early fall, although occasionally temperatures rise into the 90’s. Nighttime low temperatures in early fall are generally in the 50-60 degree range. Late fall nighttime lows average in the upper 30’s. Average annual rainfall is generally moderate. September and October are the wettest months of the season, averaging more than 3 inches per month.

Fall weather impacts deer foods from two aspects. First, early fall rains often help break late summer droughts. This precipitation often stimulates the growth of the cool season plants that deer use during fall and winter months. This is especially true for planted small grains such as wheat and rye, which deer use readily. Secondly, early cool temperatures and freezes cut short the growing season for warm season plants and decrease the amount of growth attained by the cool season plants before winter sets in; most cool season plants grow little or exist in a maintenance phase during winter. Fewer days with warm season plants available and a net reduction in cool season plant biomass can affect an area’s ability to support deer. This is probably most pronounced during years with poor acorn crops.

Nineteen plant species or plant complexes were identified as important dietary components in the fall (Table 3). These accounted for about 85% of the fall diet. Sorghum (the seed heads or grain) received the most preferred ranking. Although it accounted for less than 2% of the average fall diet, its low availability (limited to a few small plots) made it rank high in terms of preference. Three-seeded mercuries ranked high again, ranking second overall. Mushrooms comprised about 4% of the average fall diet and ranked third in preference. Coralberry ranked fourth in preference and comprised more than 21% of the diets for both fall collection periods. Acorns ranked fifth in overall preference rankings and comprised around 42% of the average fall diet during the first collection year, which was a better "acorn year" as compared with the second. Acorns accounted for about 2% of the deer diet in the fall of the second study year. Additionally, grasses such as tall fescue, bromes, wheat and rye became important in the diets.

Most food items identified in both fall collections tended to make up slightly larger percentages of the diet in the year when acorns were relatively scarce. However, the void created by the lack of acorns was generally filled by alternative forage items that were not identified in the fall diets of the better "acorn year". The largest contributer to this noteworthy phenomenon was fallen osage orange leaves which comprised more than 17% of the diet.

Winter
Cross Timbers’ winters can run the gamut from mild to severe. Long-term averages indicate that January is the coldest month, with average daily minimum temperatures dropping just below the freezing mark. Freezes are common throughout February and usually into March. Winters are usually characterized by a series of "arctic" or Pacific fronts passing through the area. Temperatures drop rapidly with the passage of a front, but usually return to above freezing during the daytime in a couple of days. It is not unusual however for the region to experience one or two relatively extended periods of extremely cold weather (1-2 weeks) each year, with daytime highs remaining below the freezing mark. These periods are often associated with varying amounts of snow or ice cover. Average monthly precipitation is generally lowest in January.

Winters in the Cross Timbers have the potential to be particularly stressful to deer in terms of forage availability and/or quality. Obviously, deer going into the winter in relatively good condition certainly should have an easier time coping with inclement weather and the scarcity of food that often accompanies it than do deer in poor condition. To a great extent, their condition depends on the habitat conditions of the preceding fall (i.e., acorn crop, abundance of cool season plants, etc.). A scarcity of desirable browse species would be extremely detrimental during this time.

Roughly 92% of the winter diet consisted of the 18 plant species or plant complexes judged to be important winter food items (Table 4). Coralberry received the highest preference ranking during winter, however, use was not consistent from year to year. During the year when acorns were more abundant, coralberry made up only about 11% of the diet. In the following year of relative acorn scarcity, coralberry comprised about 31% of the diet. The yearly variation in use probably was related to acorn availability and coralberry being used as an acorn substitute. Whatever the case, coralberry was a very important winter food item. The importance is magnified by the fact that coralberry seems to be a fairly consistent producer.

Wheat and rye were significant food items and, as a complex, ranked second in winter preference. These agronomic crops can provide significant winter forage if they are available. Greenbriers and the plainleaf pussytoes-cudweeds complex ranked third and fourth, respectively. Bromes and tall fescue made up substantial percentages of the winter diet composition, about 16% and 9%, respectively, and ranked fifth and sixth in preference, respectively. Acorns ranked seventh in preference and probably would have ranked higher had it not been for their apparent absence during the second winter collection period. Osage orange (fallen leaves) again was noteworthy since it ranked eighth in preference and made up a substantial portion of the diet composition for the second winter collection period.

Summary
Several plant species, plant complexes, and plant groups emerged as being very important to Cross Timbers deer. For instance, legumes as a group comprised 15% of the average annual diet. Their contribution to the seasonal diets was much greater in some seasons such as summer. This group includes wild beans, sweet clovers, tick clovers and lespedezas. Other plants worthy of additional mention are Carolina snail-seed, coralberry, three-seeded mercuries, and crotons. Of the 47 plants or complexes identified as important, three were important during all four seasons. These were oaks, osage orange, and the sumacs-poison ivy complex. It is reasonable to assume that a mixture of these browse species in reasonable abundance and availability is partially diagnostic of good Cross Timbers deer habitat.

It is also noteworthy that prior to this study, osage orange was thought to be a nuisance plant with relatively little wildlife food value, most of which was attributed to the use of its fruit by fox squirrels. The results of this study indicate that osage orange is of considerable importance to Cross Timbers deer.

Approximately 25% of the plant species important individually or as components of important complexes are introduced and/or naturalized plants. This is significant because the overall plant diversity of the area has probably increased over the years due to various introductions. This increase in diversity and the demonstrated use of the nonnative plants by deer indicates that the food component of deer habitat on the area probably has improved relative to the pre-introductions period.