Breeding Site Tenacity of the Chaffinch Fringilla coelebs and the Brambling F. montifringilla in Northern Finland

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Abstract
The breeding site tenacity of color-ringed chaffinches and bramblings was studied in the southern part of north Finland (64.degree.57''N, 26.degree.58''E) during 1967-1973. The breeding site tenacity of adult chaffinches was very strong. Almost all of the alive marked males bred in precisely the same area as in the previous year. In springs with superabundant food supplies and exceptional weather conditions, however, most of the younger (a + 1-yr) adults shifted eleswhere and only the older individuals remained faithful to their breeding area. Several factors may contribute to the great annual variation in the returning. The most probable explanation was that changes occur in the selection strategy of breeding sites among the younger adults in north Finland. Breeding site tenacity may decrease from south to north. For the chaffinch, this decrease was effected by the younger adults. The situation for the brambling was different. Adult bramblings lack any faithfulness to their previous breeding sites, and they nested in different areas each year. The chaffinch (a southern species) and the brambling (a northern species) displayed a significant difference in selection strategy of their breeding grounds. The importance of these findings in studying population changes was briefly discussed.