At the present stage of ornithology development hollow-nesting birds are increasingly becoming as model objects in the research on many fundamental problems of evolutionary and population biology. In recent years, a special conference was dedicated to this group of birds (Zvenigorod, 2014). In the Republic of Moldova this group of birds includes several species belonging to the primary and secondary hollow-nesting birds. Since the 1970-s representatives of this group have permanently changed their status both in species and quantity. To primary hollow-nesting birds belong woodpeckers, among which in Moldova could be met Dryocopus martius, Picus viridis, Picus canus, Dendrocopos syriacus, Dendrocopos major, Dendrocopos medius and Dendrocopos minor. Secondary hollownesting birds – is a large group of species mostly passerine that settled in hollows made by woodpeckers. Secondary hollow-nesting birds are presented at the moment by 25 species: Columba livia, Columba oenas, Otus scops, Asio otus, Athene noctua, Strix aluco, Coracias garrulus, Upupa epops, Jynx torquilla, Corvus monedula, Sturnus vulgaris, Passer domesticus, Passer montanus, Certhia familiaris, Sitta europaea, Parus major, Parus coeruleus, Parus palustris, Ficedula hypoleuca, Ficedula albicollis, Muscicapa striata, Phoenicurus phoenicurus, Phoenicurus ochruros, Motacilla alba, Erithacus rubecula. Among these birds often nest in hollows the following: Phoenicurus phoenicurus, Phoenicurus ochruros, Sturnus vulgaris, Passer montanus, Sitta europaea, Jynx torquilla. Significant changes in have been taken place in the Moldova’s landscape influenced by human activity, which resulted in the changes of avifauna in general and in the fauna of hollow-nesting species. These changes have affected the appearance of new species in nesting avifauna (Dendrocopos syriacus, Picus viridis, Phoenicurus ochruros), as well as an increase in the number of Ficedula albicollis and the disappearance of Ficedula hypoleuca. Earlier, in the middle of the twentieth century several pairs of Phoenicurus ochruros nested only on the rocky shores of the Dniester River. In later years its number and spreading began to grow very quickly and by early 2000s it became common species especially in the populated areas. At the end of the twentieth century a strong conversion of forests (deforestation of old-growth forests) took place, as well as major changes in horticulture policy, expressed in the transition from the old gardens to stunted palmettegardens where woodpeckers could not cave hollows.To date the old gardens almost completely gone. In addition, if earlier forest enterprises were responsible for hanging artificial nests for birds in all forest biocenosis, at the present time, such work is not carried out at all. It is immediately reflected in the number of species from of hollow-nesting group. So, in the middle of the last century in Central Codri, hollow-nesting birds accounted for 40% of all nesting birds in the forest, and then their share has decreased to 28%, and by 1975 they accounted for only 22% (Ганя, 1981). Due to the transformation of forest ecosystems, has decreased the number of spotted woodpecker - suppliers of hollows for secondary hollow-nesting birds. If in the middle of the last century Dendrocopos syriacus was widespread in all old gardens and its number did not concede for Dendrocopos major, then in present, its number reduced as well as the number of Dendrocopos major. However, the distribution of Dendrocopos syriacus is now associated with forests, parks and partly with forest belts because practically no more old orchards left. The number of Picus canus also decreased, it is now common mostlyin the floodplain forests, although previously nested in old gardens. Distribution of Picus viridisis limited by the northern border of the country, where 1-2 pairs are nesting. It should be noted the appearance of nesting 1-2 pairs of Dryocopus martius in the forests of Central Codri. Gradually, its numbers are growing although slowly. Currently, the number of woodpeckers in forests is very low even lower than the density of the natural hollows, where secondary hollow-nesting birds can nest, which creates the need for hanging of artificial nests for birds in forests. If we compare the number of woodpeckers in forests and in the anthropogenic landscape, than in forests is observed the greatest number of Jynx torquilla - 13,6 individuals per 100 ha against 2,8 in anthropogenic landscape, at Picus viridis (1,2 against 0), Dryocopus martius (1,2 against 0), Dendrocopos medius (9,3 against 5,7) и Dendrocopos leucotus (2,4 against 0), at the same time at 4 species of woodpeckers – Dendrocopos major (23,2 against 10,0), Dendrocopos minor (12,0 against 3,3), Dendrocopos syriacus (15,3 against1,6) и Picus canus (4,7 against 1,8) at the end of the last century the number was higher in anthropogenic landscape (Glavan, 2004). In Moldova’s forests in the middle of the last century, artificial nests were occupied by 6 species of birds: Ficedula hypoleuca, Parus major, Phoenicurus phoenicurus, Passer montanus, Sitta europaea, Jynx torquilla. The bulk of birds, nesting in nest boxes have 3 dominant species. Parus major, Ficedula hypoleuca and Passer montanus. However, by the end of 1970 Ficedula hypoleuca ceased to occupy nest boxes and the number of its in forests began to decline rapidly. Its place was taken by Ficedula albicollis, which together with Parus major dominated in artificial nests. In subsequent years, the situation has not changed, and these two species continued to be dominant in the population of hollows in forests. Within the central part of Moldova’s forests artificial nests are occupied by 6 species of birds, 3 of which (Parus major, Ficedula albicollis and Passer montanus) are the most numerous. The population of birds nesting in artificial hollows is formed firstly under the influence of anthropogenic load. Minor significance has weather during separate breeding seasons. In habitats near the settlements irreversible processes of occupation of artificial nests by Passer montanus take place, whichis undesirable rival for hollow-nesting birds. In the urban environment Parus major and Ficedula albicollis are characterized by decreasing of basic reproductive parameters (clutch size, reproductive success). Weather features, in addition to the direct influence of temperature, affect the basic reproductive parameters of both species indirectly through the availability and abundance of food items. The effect of abnormal heat on the natural dynamics on the number of hollownesting birds in Moldova’s forests is not yet clear, though some literary sources report a notable reduction in the number of Dendrocopos medius and Parus major in forests of Belarus in response to extreme weather conditions. As a possible causewasidentified some biological features of these species, for example, the fact that they do not make feed stocks for the winter time. Subsequently, their numbers recovered to average of long-term levels (Косенко, 2014). The work was performed within the fundamental project 15.187.0211F.