For the Birds Radio Program: New Mockingbird Research
New research is indicating that mockingbirds and their relatives produce more varied and complex songs when they live in more variable climates than where the climate is more predictable.
A female bird has a vested interest in choosing, of all the males available to her, the one most likely to defend the highest quality territory, to father the most genetically fit babies, and to provide the highest quality food and protection for her young. In areas with unpredictable and highly variable climates, it may be even more urgent than in milder areas for females to choose the fittest mates if their own huge investment in their chicks is to be successful. But what factors can a bird use to predict which male is the best choice?
In a paper published this summer in Current Biology, Cornell Lab of Ornithology researchers found that birds belonging to Mimidae—the mockingbird family—have more elaborate songs when they live in more variable and unpredictable climates than when they live in more predictable climates. Mimids are famous for the many elaborate imitations they incorporate into their songs. The most famous species, the Northern Mockingbird, was Thomas Jefferson’s favorite bird because of its intelligence and ability to mimic. He kept a pet mockingbird named Dick in the White House, and boasted in his Notes on the State of Virginia that Great Britain had nothing to compare with this bird’s vocal abilities. Another mimid, the Brown Thrasher, is listed in Ripley’s Believe It or Not! because bird song authority Don Kroodsma documented one individual producing 2,400 different songs.
How can a bird’s song be a reliable indication of his general fitness for fatherhood? One possibility is that song serves as a sexual signal in the way that Red-winged Blackbird epaulets or Blue-footed Booby feet do. The color of plumage and bare parts in some species contains information about a bird’s physiological condition and overall fitness, which can help or hinder his defense of a quality territory. Mimids in general have fairly dull plumage and little if any sexual dimorphism, so males presumably don’t rely on physical displays or colors to attract mates. But their songs are used both in territorial defense and in attracting mates, and, as the study found, mimid songs seem to grow more elaborate when climate becomes more variable, which could cause more intense competition among males. Those up to the task may be more up to the tasks of raising babies, too.
Mimid songs may also serve as valid indicators of each male’s ability to learn and innovate, qualities reflecting his basic intelligence and perhaps how well he can assess current conditions and decide on the best times and places to establish a territory and initiate nesting.
The researchers didn’t consider one other possibility. Because mimids so accurately mimic the sounds of each area they’ve lived in, adding new songs to their repertoires year after year, the songs may be a clear and simple announcement of all the experiences they’ve survived over their lifetime. I sometimes think of them as the Othello birds—winning their love by telling the story of their life. The question will provide fodder for research for years to come, because, from the catbird’s seat, the birds keep singing on without ever telling us what it’s all about.