Yellow Fellow

Day 199: Although many birds molt only once a year, others exchange their drab winter clothes for more attractive colours during mating season. Their winter garb helps to camouflage them when trees are bare, but obviously, this is less necessary when there is plenty of foliage in which to hide from predators. Then the birds can afford to put on the best show in the hopes of attracting a mate. This seasonal colour change is hormonally triggered, and a dramatic example can be seen in American Goldfinches (Spinus tristis). The vivid yellow of the males seems almost to glow, owing to the fact that the thin feathers overlap in such a manner that the yellow tips are backlit by light reflected from the feathers' white bases. The female also takes on a yellowish tinge, although not nearly as bright as the hue of the male, and thus as sole incubator of the eggs, the female benefits by retaining a large portion of her camouflage during this crucial period. Juveniles are similar in colour to females.