Interspecific competition among the secondary hole-nesting birds under the conditions of large interannual fluctuations of spring temperatures in Karelia

Data on the reproduction of birds in bird boxes (n=167-196) in Karelia in consequent years with drastic changes in spring temperature were analysed: 1975 - extremely early and warm spring, 1976 - late and cold one, 1977 - with medium indices. The changes in fertility, reproductive success and the number of Great tit Parus major L. (77 nests), Pied Flycatcher Ficedula hypoleuca L. (171), Redstart Phoenicurus phoenicurus (L.) (10) and Wryneck Jynx torquilla L.-(6) were estimated. It was shown, that under the unstable conditions of the North, competition can make a considerable contribution to the dynamics of the population characteristics of birds and serve as one of the significant elements of the mechanism of their number regulation. Its influence is enhanced due to the convergence of the time of the breeding start of wintering and migratory birds in a year with late spring. The result of that is the rise in the number of nests lost due to anxiety or ruined by competitors, and increasing proportion of recycled clutch smaller in size and late on terms. These contributed to the fall of population productivity, the growth of the necessary reproductive effort in a significant part of individuals as well as the increase in the proportion of late broods, changing plumage at late time. After the year with early spring the number of all secondary hole-nesting birds grew, but after that with late spring, it reduced. The most significant decline in the population (in 3 times) was showed by Great tits – species with bicyclical reproduction. Because of the high percent of late second and repeated nests in 1976 the large number of individuals moulted at late time and under the extremely adverse conditions and it resulted in their increased mortality.