From the Cornell Lab of Ornithology in the USA:
Female cardinals love a dapper fellow in red. Photo by A Wing and a Prayer via Birdshare.
The Redder the Better
In many areas of the eastern United States, handsome Northern Cardinals are already singing to attract mates. A bird so visible in the winter landscape begs the question, “How does a flame-red bird that often nests close to the ground manage to be common in the eastern United States?” We are often asked how this conspicuous species has been so successful, despite its low rate of nesting success. Typically, less than 40% of nests fledge at least one young.
The answer may lie in their long breeding season. Cardinals do not migrate and often begin the nest-building process as early as late February. They can continue nesting into late August in some areas, which affords opportunities to nest multiple times. Another factor could be that cardinals are habitat generalists. They can nest in open woodlands, dry shrubby areas, or even the suburbs. Their nests are placed in live trees, shrubs, or vine tangles, anywhere from 1–15′ high. A recent study in Texas* revealed that cardinal nest sites were not particularly different from random sites, suggesting that they may not be limited by suitable nesting locations. However, there seem to be benefits from nesting higher up and later in the breeding season, both of which probably thwart some potential predators. Cardinals also tend to nest in the denser parts of trees or shrubs, which may provide some vegetation cover.
But how is it adaptive for the males to be such colorful and obvious songsters? The flamboyant males sing from high perches and do not trade their breeding plumes for a drab winter coat. According to research compiled in The Birds of North America Online, brighter males have higher reproductive success and better territories, and plumage brightness is positively associated with parental care. The intensity of the cardinal’s red coloring is related to its diet, and bright coloration is a signal to females that the male probably holds a good territory (although this is not necessarily true for urban areas). The females, through a process called sexual selection, have selected for this bright coloring in the males. And because the female’s colors are muted, they provide her with a protective camouflage that the male lacks. This also aids in nest concealment when she is incubating. Furthermore, juvenile and adult cardinals tend to have high survival rates, possibly because they don’t endure the stress of migration.
Against all odds, the Northern Cardinal is marvelously adapted to its environs. So the question is not “Why are they so successful?” but rather, “Why wouldn’t they be?” If you are lucky enough to find a cardinal nest this year, won’t you help us learn more about this fascinating species by monitoring it with NestWatch?
*Sperry, J. H., D. G. Barron, and P. J. Weatherhead. 2012. Snake behavior and seasonal variation in nest survival of northern cardinals Cardinalis cardinalis. Journal of Avian Biology, 43: 496–502.