Birdsong and Climate

Introduction

Birds that live in more variable climates sing more sophisticated songs.

Podcast

Birdsong and Climate

Transcript

Climate-enhanced bird songs. I'm Bob Hirshon and this is Science Update.

[SFX: Simple bird song - scaly-breasted thrasher]

Some bird songs, like that of the scaly-breasted thrasher, are simple and repetitive. But its cousin the brown thrasher sings a much trickier tune:

[SFX: Complex bird song - brown thrasher]

New research suggests that a bird's native climate can determine its musical chops. Behavioral ecologist Carlos Botero of the National Evolutionary Synthesis Center in Durham, North Carolina led the study, which compared different species of mockingbirds.

Botero:
We found that species living in more variable and unpredictable environments tend to also have more elaborate song displays.

He says that female birds in such climates may be especially interested in mates who can learn and adapt easily, forcing the males to show off their brainpower with sophisticated melodies. I'm Bob Hirshon for AAAS, the Science Society.

Making Sense of the Research

Bird song is a trait that's driven by sexual selection, a kind of natural selection that involves competition within a species for mating opportunities. Male birds use songs for two purposes: to attract females and to warn away other males who might poach on their territory. In both cases, a good song can help a male bird father more offspring.

This study shows how an external issue, like climate, may influence sexual selection. It's assumed that no matter what the climate, the choices of female birds drive the evolution of male birds' songs. In other words, a song is only as good as female birds think it is. Yet, when you compare the songs of birds in mild, stable climates to those of birds in unpredictable climates, it's a little like comparing a middle-school talent show to the final round of American Idol. The simple songs that win the hearts of females in one location just wouldn't cut it in another.

Why? Botero offers two possible explanations. According to one hypothesis, harsh, variable climates demand more complex survival skills than stable climates. One aspect of surviving is learning. Since bird songs require a lot of brain power to learn, it's possible that the males use sophisticated songs to advertise their superior intellects. On the other hand, females in unpredictable climates may just be more choosy about their mates in general, forcing the males to work harder to impress them.

But what's to stop all birds from developing elaborate songs? Won't the males with the most sophisticated songs do best, even in a low-stress climate? Scientists have actually thought about this question for many years, and they've concluded that trickier songs may come with a cost. It takes up physical space in the brain, in the form of specific areas devoted to song learning. It also takes time for a bird to learn and practice songs—time that could be spent learning other essential bird business. Botero says that in order for a bird to devote a big chunk of its body and its life cycle to something like singing, then singing must be incredibly important. In places where it isn't, learning flashy songs may actually become a disadvantage.

Now try and answer these questions:

1. What is sexual selection? How does it apply to bird song?
   
2. How do the songs of male birds vary with climate?
   
3. What are the possible reasons why climate affects female mate choice and, therefore, the complexity of male songs? Which do you find more likely?
   
4. How might climate change affect the lives of birds, with respect to the information you just heard?

Going Further

In the Science Netlinks Science Update lesson Cassowary Calls, you'll hear about efforts to study the rare and often inaudible call of an elusive bird.

The PBS resource Flying Cassanovas celebrates the extraordinary antics male bowerbirds get up to when courting a female. Users will find sections about bowerbird research, whether or not the bowers they build are works of art, and sexual selection.

The National Geographic News article Are Flashy Male Birds Threats To Their Own Species? highlights a potential cost of colorful feathers that some male birds use to attract mates.