Ardea
Official journal of the Netherlands Ornithologists' Union

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Tinbergen J.M., van Balen J.H. & van Eck H.M. (1985) Density dependent survival in an isolated Great Tit population: Kluyvers data reanalysed. ARDEA 73 (1): 38-48
Kluyver and co-workers (1971) collected census data in an isolated Great Tit population from 1956 until now. Removal experiments, both with fledglings and adults, have been carried out to detect density dependence in local recovery rates. The data, partly analysed by Kluyver (1971) and Van Balen and Van Eck (in Klomp 1980), were reanalysed. The results shed new light on the factors- involved in the regulation of numbers in the Great Tit population of Vlieland. . Both fledgling and adult recovery rates are related to the winter seed stock, estimated as the national beech-crop index. Since no seed bearing beeches occur on Vlieland, a related causal factor must be involved. Potential candidates are Birch and Black Alder seeds. 2. Fledgling local recovery rate is density dependent, although the effect is small. Separate analysis of the recovery rates of first and second-brood fledglings reveals that the recovery rate of second-brood fledglings is depressed by first-brood fledgling density. No density-dependent effects were found within the category of first-brood fledglings. These two effects lead to a selection pressure for density-dependent effects on the occurrence of second broods as shown by Kluyver (1951). No effect of adult density on fledgling recovery was detected: 3. Adult recovery rate is not density dependent, as described by Kluyver (1971), but negatively related to the number of fledglings annually produced per pair in years when the winter seed stock is low. In years with a high winter seed stock no such effect could be shown. This finding implies that Great Tits suffer a substantial cost of reproduction in years with low winter seed abundance (the recovery rate is reduced by 5 per cent per extra fledgling produced).


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