Effects of supplemental feeding and female age on timing of breeding in the Alpine Accentor Prunella collaris

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<jats:p>Supplemental food in the form of millet seed was provided to 1‐year‐old and older (2:2‐year‐old) female Alpine Accentors <jats:italic>Prunella collaris,</jats:italic> and the effect on timing of breeding was studied over four breeding seasons in central Japan. Only 1‐year‐old females responded to the supplemental food: additional food advanced their settlement date, the onset of the development of a cloacal protuberance and laying date. In contrast, no effect of the experimental feeding was found on the timing of breeding in older females and they invariably bred earlier than 1‐year‐old females. Having settled on the breeding grounds, females developed the cloacal protuberance and retained it for about 1 month until the last egg in the first clutch was laid. The development period of the protuberance corresponded to the copulation period. Because the copulation period was not shortened by extra food and no significant difference occurred in either of the two age classes, it is necessary for earlier breeding birds to accumulate the nutrients needed to form the protuberance as well as the eggs. Although older females relied less on supplemental food, they were significantly heavier and formed the cloacal protuberance earlier than 1‐year‐old females. One‐year‐old females depended more heavily on supplemental food than did older ones and the duration between settlement date and the onset of development of the protuberance of 1‐year‐olds was reduced by additional food. These results raised the possibility that older females fly from their wintering grounds carrying some food reserves which they can use for forming the protuberance, while 1‐year‐old females collect the food needed for forming it on the breeding grounds.</jats:p>

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  • Ibis

    Ibis 137 (1), 56-63, 1995-01

    Wiley

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