Grazing behavior in ungulates: Current concepts and future challenges

An early focus on ungulate foraging behavior occurred in the 1940's as scie ntists began quantifying the activities of livestock and wildlife to addres s production goals. Interest resurfaced in the 1970's and continued as inve stigators pondered behavior related hypotheses at evolutionary, ecosystem, and plant/animal interface levels. Presently, many grazing land environment al concerns are related to the selective foraging habits of ungulates and t heir poor distribution about the landscape. These two facets of ungulate be havior serve as the impetus for many of today's research efforts. and scien tists in the field need to develop a theoretical framework to address these problems. The theories of optimum foraging and adaptive rumen function wer e offered to explain evolutionary patterns of forego selection among herbiv ores, but they lack the specificity needed by range and pasture managers at relevant space and time scales. While post-ingestive feedback mechanisms c ause aversions to toxic plants, and some species of herbivores have develop ed means of neutralizing harmful compounds, the mechanisms stimulating the development of forage preferences in the absence of aversive compounds are not clearly understood. Ungulates also exhibit selective patterns of spatia l use about the landscape. In some environments where necessary resources ( water, shade, forage. minerals, escape topography or cover) are scarcer are as of activity will be focused about these limiting elements. Many of the h erding ungulates, however, repeatedly regraze certain areas and avoid other equally suitable portions of the landscape. Research suggests these habits elevate the animal's nutritional status by curtailing advances in plant ph enology and removing the hindrances of cured forage from the grazed parches . Such a scenario increases landscape diversity and may enhance species ric hness and accelerate nutrient cycling in the grazed areas by maintaining ve getation in an earlier stage of succession. Recent investigations suggest t hat ungulates ran retain and use spatial memory to expedite foraging, and c an associate shapes and colors with the presence or absence of food. These skills have been clearly demonstrated in small, well controlled environment s, but patterns of behavior and distribution in extensive landscape setting s are poorly understood. The recent advances in geographic information syst ems and global positioning systems will assist us greatly in our analyses o f ungulate behavior at landscape levels of resolution. Pasture and landscap e managers are beginning to recognize many of the innate habits and prefere nces of livestock though, and are exploiting these behaviors to affect plan t succession, control weeds, and manipulate forage quality or structure of the plant community. There is much left to learn, but as we make inroads in these endeavors, the value of grazing animals can only increase.