Effects of Supplemental Feeding on Red-winged Blackbird (Agelaius phoeniceus) Fledgling Size
Hollman, Christopher John
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Traditionally, species that exhibit asynchronous hatching do so as a means of brood reduction in times of food shortage. Such is the case with the Red-winged Blackbird (Agelaius phoeniceus). Red-wings, a~though hatching asynchronously, tend to display very little variation in within nest fledgling size, but much greater variation in fledgling size can be seen among nests. The aim of this experiment is to explore whether the internest variation seen in A. phoeniceus is a result of differences in (1) the physiological ability of the hatchlings to process food or (2) in the food supply being delivered to the hatchlings. One hatchling from each nest in this study was supplemented with 10-15% of its body mass in common red worms, three times daily, to determine the effect of supplemental feeding on fledgling size. The results show that supplementing the food supply causes an increase in growth of the hatchlings given extra food, as well as an increase in the gr9wth of its nest mates, due to more overall food being delivered to the nest. The increase in hatchling mass was also evident in greater linear dimension of forearm and tibiotarsus lengths, indicating that the extra food was being used for actual growth of the hatchling, rather than simply making the hatchling ''fatter.'' From these and other observations, it can be concluded that variation in food supply among nests . co~tributes significantly to internest variation in fledgling size of the Red-winged Blackbird.