Meeting Abstract
Plumage coloration can be an important signal of health, nutritional condition, parental quality, and reproductive success. In young birds, the development of plumage coloration is often condition dependent and based on factors such as amount of parental care and stress hormone levels. Offspring raised in small or large broods may differ both in the amount of parental care provided and stress exposure. In some previous studies, young raised in larger broods exhibited higher stress hormone levels and reduced growth rates; however, results have been inconsistent. We experimentally manipulated brood size of Eastern Bluebirds (Sialia sialis) and predicted that nestlings in enlarged broods would experience more competition for food, resulting in lower nestling body mass and less feather ornamentation. Contour feathers from the chest and rump were collected and coloration was measured with a spectrophotometer. Chest feather coloration in bluebirds is a result of melanin pigments and the blue-ultraviolet of the rump feathers is a structural color. Female nestlings in enlarged broods had more ornamented chest feathers, but less ornamented rump feathers. These opposing results may be due to differences in the source of coloration for chest and rump feathers. Coloration of male nestlings was not impacted by brood size manipulation. Growth rate for nestlings of either sex was unrelated to brood size, suggesting that parents may be able to compensate for a larger brood size. In conclusion, female plumage color in the first year may reliably signal stress exposure during development.
