Female house wrens sing to defend their nest sites from intruders.
Why female songbirds sing. I’m Bob Hirshon and this is Science Update.
Male songbirds sing more than females do, and most research has focused on how their songs help them maintain their territories and attract mates. But females of some species, like the house wren, also sing.
(female house wren song)
If you go into the field expecting to see patterns that you see in males, it can be really easy to miss these rich interactions that are going on between females, too.
That’s Michigan State University behavioral ecologist Cara Krieg. She and colleague Thomas Getty report in Animal Behaviour that female wrens sing the most during the egg-laying stage of the spring, perhaps to ward off rival females attempting hostile takeovers of their nests. And it seems to work: females that sang the most in response to playback of recorded wren song suffered the fewest egg losses. I’m Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
You're probably familiar with the concept that male songbirds sing for all sorts of reasons, from attracting mates to warning off potential rivals. It turns out, though, that female songbirds also will sing to keep away potential rivals.
Cara Krieg, a doctoral student of zoology, has been studying female birdsongs and female-to-female aggression. She believes that female aggression has been an overlooked phenomenon in behavioral ecology; aggression has historically been pegged as a characteristic to look for in males. She cited her work as an example of the value of approaching scientific research from different perspectives.
House wrens are noted for their aggressive behavior when it comes to nest location. If another bird has a nest hole, the house wren will peck and chase off the adult bird and will pierce eggs and throw them and very young nestlings to the ground in order to acquire the real estate for their own use.
Acording to Krieg and her colleagues, female house wrens that sang more during the onset of egg laying lost fewer eggs to other house wrens than those that didn't sing as much. In addition, they found that the female house wrens in the group they studied sang most and initiated most vocalizing bouts when they heard the vocalizations of other house wrens.
Traditionally, birdsong has been seen as a male behavior. Recent research carried out by Odom et al. in 2014 turned this belief on its head. This research found strong evidence that the common ancestor of all songbirds was a singing female, meaning that female song has existed for millions of years.
Krieg and her colleauges are building on this research by carrying out this study at the W.K. Kellogg Biological Station in Michigan. In this region, the researchers visited nest sites and conducted playback experiments in which they played recordings of wren song. As a result of these experiments, they found that female song is surprisingly common in the study population (61.6% of females were observed singing at some point). In recordings of 2,183 female songs, 11 different song types have been documented so far. Some of these song types seem to be shared by females in other populations. They also found that female song is completely different from male song.
The researchers think that the female house wrens sing to defend against other house wrens. It appears to be most common at the start of egg laying. Their aggression seems to pay off because more of their eggs survive and nestlings grow strong enough to migrate in the fall.
Now try and answer these questions:
- Why has Cara Krieg chosen to study the birdsong of female house wrens?
- When did the female house wrens appear to sing the most? Why?
- According to Odom et al., who is the common ancenstor of all songbirds?
- How did Krieg and her colleagues carry out the study?
- What did their experiments show?
- Can you think another way of studying female songbird behavior? How would you go about it?
You can learn more about birdsong by listening to the Birdsong and Climate Science Update.
For another look at aggression in birds, you could have your students check out the Cowbird Nestmates Science Update, which looks at how cowbirds will lay their eggs in other birds' nests and leave the strangers to care for their chicks.
You also could extend the ideas in this Science Update by guiding your students through these other Science NetLinks resources.