NIDICOLOUS AND POST-NIDICOLOUS MORTALITY OF YOUNGS FROM ASYNCHRONOUS BROODS OF SOME PASSERINE BIRDS (PASSERIFORMES)

An analysis of factors causing the death of late-hatched nestlings of Great Tit (Parus major), Blue Tit P. caeruleus) and Tree Sparrow(Passe r montanus) at different stages of ontogenesis is given. The use of fa ctor analysis enabled us to reveal two factors determining the variati ons of some characters of late-hatched nestlings. The first one charac terizes <<the peculiarities of late-hatched nestlings>> ( hatching int erval, differences in weight and the length of bill as compared with t hese characters in the first-hatched nestling), the second one are <<t he conditions of development>> (degree of asynchrony and size of a bro od, age of a female, reproductive cycle). Elimination of late-hatched nestlings is assumed to be determined by the first factor. The predomi nance of former first-hatched nestlings among the birds breeding for t he first time a year later was revealed. The different mortality of mo rphologically different fledglings in a brood is assumed to be the cau se of this fenomenon. Thus, The elimination of fledglings developed in pessimum conditions increases the reduction of a brood.