The entire territory of Northern Kazakhstan has been used for agriculture, causing deep transformation of landscapes, especially forest steppe, and degradation of animal biotopes. It is therefore necessary to comprehensively elucidate the consequences of this process. The development of virgin land and subsequent intensification of agricultural land use, eventually resulting in universal replacement of natural ecosystems with agrolandscapes have reduced habitat availability for many animals, wherefore establishment of game reserves, later on transformed into zoological reserves, was initiated. On the basis of studies carried out in the region in the 18th-20th cc. and the analysis of an extensive pool of zoogeographical data, we demonstrate stages in the loss of the zoological diversity of the forest steppe zone, and analyze quantitative and qualitative changes in the fauna of Mamlyutsky, Smirnovsky and Sogrovsky forest steppe zoological reserves in the North Kazakhstan region. The key factors behind the spatio-temporal decline in the number of animal species and their abundances since the foundation of the protected areas were identified. Systematization and analytical treatment of the results of long-term zoogeographical surveys of the above-listed nature reserves coupled with official statistical data and the findings of the authors' own field surveys (animals and birds counts; assessment of human impact on biotopes) in 2010-2016 allowed to reveal a downward population trend for a majority of species of southern and atypical kolok-type (with groves) forest steppe. The role of other negative factors - fires, poaching, fisheries (in addition to the dominating agriculture-related factors), has also increased. A number of actions to reverse the situation and stabilize the abundances of protected species are proposed for each of the nature reserves. An assumption is made that the only environment-friendly scenario allowing to preserve the representativeness of the nature reserves' fauna would be to reduce the excessive agriculture-related pressure both within the protected areas and in buffer zones.