Seasonal Auditory Changes Differ Between Male and Female Sparrows

Auditory systems of male and female house sparrows differ depending on the seasons, finds a new study.

Researcher Megan Gall, from Georgia State University, tested the auditory systems of both sexes of sparrows during breeding and non-breeding seasons. She measured the frequency selectivity and temporal resolution of the birds. Frequency selectivity is the ability to identify different frequencies in a complex sound, whereas temporal resolution is the ability to tell sounds apart that are very close together in time.

Gall found that the male sparrows have the same frequency selectivity and temporal resolution across breeding seasons. During fall season, both the male and female sparrows do not have any difference in frequency selectivity and temporal resolution. But the females have better frequency selectivity and worse temporal resolution in the breeding season.

This indicates that seasonal plasticity (the ability for neurological systems to change) is not just inside the parts of the brain that control auditory function, but is also present in the ears and the auditory nerve of the auditory system.

Humans also face similar changes, where the auditory systems differ in women during their menstrual cycle. Researchers suggest that the changes might have evolved over time for various reasons. One reason Gall cites is that the body could not maintain the kind of tissues involved in hearing.

"In the ear, there are huge electrical gradients between the hair cells and the fluid that's bathing the hair cells in the ear, and that's expensive to maintain," she said.

Gall suggests another possible reason for the birds processing different auditory systems. During non-breeding season, it is really difficult for the birds to find food. Birds make calls in order to let other birds know where the food is. They make calls in the same way so that the other birds respond to the signal.

A different kind of auditory system is also required when the birds make alarm calls to indicate the presence of the predator.

Gall hopes the study will help in understanding the ability of parts of the human nervous system to change.

The findings of the study are published in the journal Proceedings of The Royal Society B.