Abstract: Brandt's vole is one of the major pest：rodents in typical steppe in Inner Mongolia，China．The stomach contents of the voles were analyzed to determ ine the natural diets by the method of microhistological identification in April and July of 1989．The Sampling site is located at Hexiten Banner．Inner Mongolia (43°24' N．116°46' E)．
In spring．the major plant species(more than 1% of the vole diet) consumed by the voles included Aneurotepidium chinense, Stipa krylovii，Agropyron cristatum，Carex duriuscula．Potentilla acoulis，Artemfsia frigida，and lxeris ehinensis．0f these，Aneu-rolepidtum chinense constituted 55.40% of the vole diet，and Agropyron cristatum did 27.62% ．Aneurolepidium chinense was the vole's favourite food in spring．In summer，the major food plants of the voles consisted of Aneurolepidium chinense，Melissitus ruthenica。Heteropappus altaleus，Artemisia,frigida，Agropyron cristotum，Potentilla tanacetifolia，Cleistogenes squarrosa，Stipa krylovii，and Potentilla bilurca．Of these，Aneurolepidium ehinense constituted 40.34% of the vole diet，and M elissitus ruthemea did 28.95 %．The voles also ate favouritely aneurolepidium chinense in summer．In the period of plant growth，the voles mainly ate plant leaves．The voles utilized a small amount of plant roots (1.95% of the vole diet) only in spring．So the vote diets showed obvious seasonal changes．In addition，the voles ate 22 plant species in total in spring and summer．but the voles took 7-9 species of them as the major food，and specialized on 2-3 species (more than 70 of the diets)．The value of the similarity index between the diet eomposition and plant species composition of the vegetation was 0.3877 in summer．It could be concluded that there was a great difference between these compositions．The difference was caused by food selectivity of the voles．All of these indicated that the vole diets had obvious characteristics of preference．
The seasonal changes of the vole diets were the resronses to the changes of the food resources provided by the vegetation. The species diversi of the vegetation was lower in spring．the relative density of monocotyledons was 76.09% ，and there was a scant supply of food in the habitat，therefore，the bulk of the diets consisted of monocotylcdons (91.97% )，in the mean while the voles consumed a small amount of plant roots. With the increase of the proportion of the dicotyledons and species diversity in the vegetation from spring to summer，the voles ate about equal amount of dicotyledons and monocotyledons in summer． The voles preferred, the plants which contained more quantity of proteins and mineral elements．The major food plants of the voles contained plentiful silicon．It probably was relative to the continued abrasion and growth of molars in all Iives of the voles．The nutrient content of plants was one of the prlncipal factors influencing the food selection of the voles . The voles took optimal foraging strategy while they foraged their food. In summer, the major food of the voles consisted of two parts．productive food plants that could meet the minimum nutritional needs of the voles, and filler plants with higher frequencies in the vegetation that could shorten foraging time of the voles. The vole selected most of the plants whose frequencies were higher than 40 ．The plant frequency could influenced the food selection of the voles．

Key words: Brandt's vole (Microtus brandti), Food habits, Foraging behavior

摘要： 通过胃内容物显微组织学分析法，研究了内蒙古克什克滕旗阿其乌拉地区布氏田鼠春季和夏季的自然食性。该鼠于春季和复季都最嗜 食羊草，但食性有明显的季节变化，对食物有强烈的选择性特征，专化现象较为明显。植被的物侯变化和植物体的蛋白质含量以及硅等矿质元素的含量是影响布氏田鼠进行选食的主要因素 文中还讨论了布氏田鼠的最优觅食行为。

关键词: 布氏田鼠, 禽性, 觅食行为