COLONIAL AND SOLITARY NESTING CHOICE AS ALTERNATIVE BREEDING TACTICS IN TREE SPARROW PASSER-MONTANUS

1. A total of 250 nestboxes were arranged, 25 with 50 m separations to simulate solitary breeding and 25 3-5 m apart to imitate colonial bre eding in each of five plots in order to study tree sparrows (Passer mo ntanus L.) in a suburban area of Budapest, Hungary (19-degrees 04'E, 4 7-degrees 41'N). Nestlings and adults were banded with coloured rings, and breeding performance, rate of return and recruitment were analyse d. 2. Throughout the 6-year period of the study 34 single, 209 double and 137 triple breeding events were found in colonies, and 24 single, 130 double and 93 triple breeding events were found in solitary nests. Mean yearly total production of breeding pairs was 10.75 eggs and 7.2 3 fledglings. 3. Both double- and triple-breeding parents produced mor e eggs and fledglings colonially than in solitary nests in their first broods, but this was reversed in their second and third broods. 4. Th e majority of breeding pairs chose colonial nesting in first broods. A higher rate of colonial than solitary breeders changed nesting situat ion between broods, so the majority of breeding pairs nested solitaril y in third broods. 5. Both colonial and solitary females whose reprodu ctive performance was low shifted nesting situation between subsequent broods. Colonial pairs, which moved to solitary nests benefited by ch anging, solitary pairs benefited by retaining their nesting situation in subsequent broods. 6. The majority of returning females chose colon ial breeding and retained it through the season in their first breedin g year. Both colonial and solitary females of low productivity shifted nesting situation between subsequent breeding years. 7. Colonial fema les benefited by between-year changing because their productivity was higher, and they reared more recruiting young per brood in solitary ne sts than females which retained colonial nesting. Conversely, solitary females benefited by retention of their nesting situation. The rate o f shifting females increased in colonies and decreased in solitary nes t spacing in subsequent breeding years and, as a consequence, the majo rity of females bred in solitary nests in the second and third years o f their return. 8. The seasonal and lifetime trend in preferring solit ary breeding reflects a result of alternative breeding tactics which s eems to be a viable reproductive strategy for tree sparrows.