A recent study, co-authored by Jeffrey Lucas, professor of biological studies at Purdue University, shows that some birds may snub a suitor’s call if it’s not the season d’amour. The research shows that some bird species have degraded hearing ability in the fall—when it’s not mating season—which Lucas said has potential implications for hearing loss in humans. The next phase of his research is to determine whether hearing differences exist between the sexes.
I talked to Lucas about his bird study, filtering out sounds and why female humans may hear better (unbeknownst to them) at certain times of the month.
What’s the significance of these findings?
We're trying to understand how habitat affects the ability of birds to hear; how plastic the peripheral auditory system is across seasons; how variable the hearing of these birds is from say, the mating season to the non-mating season; and we’re looking at sex differences. It’s important in trying to understand how natural selection molds the sensory biology of species. At a different level, it helps us understand our own hearing. Understanding birds at a really deep level gives us an insight into ourselves.
If these birds are hearing better at some times than others, is it considered habituation? Or selective hearing?
Neither. We’re looking at broader changes—it’s in the inner ear and the brain stem. Those parts act as filters. You’re bombarded all the time with sound, and your brain doesn’t get all of the sounds that impinge on your ear. Your peripheral auditory system filters out stuff that really doesn’t matter and accentuates stuff that does.
And this filtering changes in different seasons for birds?
The magic of seasonality is that what matters in December is very different than what matters in April. It’s not like a chickadee can’t hear in December. They still hear predators and contact calls. But in April, they are exquisitely tuned to the specific frequencies that matter desperately in terms of mating. The flip side—why should you down-regulate part of your hearing? The answer is that terrific hearing requires a certain metabolic investment. You pay that extra price when it matters, but in the winter, there are more important things to do, such as--if you’re a bird—finding food. It also appears that estrogen plays a role.
Is this just in birds?
It’s not just in birds. Female fish can hear the song of the male, but can’t hear the low frequency of predators. So in these fish, it’s the females that are changing the hearing, and it’s estrogen that’s driving it. It’s also in mammals. It has been shown in female humans that your hearing acuity is highest when your estrogen levels are high. The point is that there’s an adaptive reason why you should pay attention to certain sounds at certain times of the year and not at others. You’re not turning your ears off, but you’re fine-tuning your capacity to process the different types of sounds.
So what does it mean for female humans?
To the degree to which female humans pay attention to vocal cues from potential mates, what evolution has done has to up-regulate their capacity to hear vocal aspects of males when it matters.
Do females notice this is happening?
Probably not. Do you know the studies done on olfactory cues? Remember the sweaty t-shirt? There’s no question now that females have the capacity to differentiate between males based on pheromones, but 20 years ago people would think you were crazy suggesting that. We’re surrounded by signals—pheromones--that have an impact on our lives, but that doesn’t mean we’re conscious about them. The olfactory cues are a perfect example of something you respond to, but not consciously. These auditory cues are exactly the same thing. Your sensory world is different—much broader--than your cognitive world. We have these capacities, we just don’t pay cognitive attention to them.
Click here to read my recent post on musicians’ hearing.