Singing mice live in the cloud forests of Central America and are known for their spectacular vocal displays – mostly by males who want to repel rivals and attract females. According to Bret Pasch at the University of Florida, these neotropical singing mice get the most attention from females when they deliver a flashy performance, using high-pitched vocal trills. The study of Alston’s singing mouse appears online June 2011 in the journal Animal Behaviour.
Unless you are a female mouse, you may need to cup your ears to hear the high-pitched trill in these videos.
The males’ prowess could give female mice clues to a potential mate’s physical quality. This may even extend to humans, where studies have shown that men’s dancing may influence women’s impressions of their quality as a mate. A 2005 Rutgers University study showed that women could identify men with better body symmetry – an indicator of developmental stability – just by watching their dance moves.
Elaborate courtship displays require fine coordination of the nervous, neuromuscular and cardiac systems. There is increasing evidence that females evaluate male skills during these displays to determine their overall vigor.
When it comes to singing, it’s easy enough to identify characteristics that make a human excel – an exceptional range, or the ability to hold a high note, for example – but mice have different criteria. Pasch explained:
What makes a great performance is how rapidly males can repeat notes while maintaining a large range of frequencies of each note. Female preference seems to be based on how well males perform songs.
In the study, Pasch and his team demonstrated that, like birds, the Alston’s singing mouse, Scotinomys teguina, has biomechanical limitations to its trills: The faster it trills, the lower the range of frequencies in each note. Conversely, singing with high frequency bandwidths limits the speed with which it can repeat notes.
Pasch uses a textbook analogy: handclapping. The slower you clap, the louder each clap can be because you have time to pull your hands apart to generate power. As one claps faster, there is less time to generate power. Beyond a certain rate, one cannot clap both loudly and quickly.
Watch the ears of this female mouse. Do you think she likes what she hears?
The similarity to birds surprised Jeffrey Podos, a biologist specializing in vocal behavior at the University of Massachusetts Amherst. Podos said:
Mice and birds sing using completely different vocal mechanisms, and so the similarity in song patterns is very much unexpected. It will be interesting to try to identify similarities in vocal mechanics between birds and mice that could explain the convergent pattern.
In the second component of the study, Pasch and his team demonstrated that male sex hormones, also called androgens, affect how well mice can sing. By neutering the male mice, then giving synthetic hormones to some of them, the researchers showed that mice without hormones weren’t able to perform as well as their counterparts.
The mice who didn’t receive hormone replacement had slower trill rates, and their notes covered a smaller range of frequencies. The researchers suspect that androgens may act on the jaw musculature and diaphragm to influence the rate of mouth movement and force of respiration. The role of androgens in modulating song performance has not been previously studied, Pasch said.
In the third part of the study, Pasch and his team showed that female mice preferred better singers. By taking a normal mouse song and manipulating it electronically to pack in more notes per second, the authors created a song they predicted would appeal to females more than the song at normal speed. They then isolated female mice in a two-way test chamber, where a speaker at one end played the normal song and the other played the enhanced song with the higher trill rate. Pasch said:
We found that females approached more quickly and spent more time near the speaker playing the faster trill. This suggests that females have the capacity to distinguish slight variations in male motor performance and use that information to guide their behavior.
Female preference for more difficult songs is notable, Podos said; researchers have never before documented this type of preference in mammals.
Summary: A study of Alston’s singing mouse by Bret Pasch, University of Florida, and his team shows that females likely evaluate males during their singing displays to gauge vigor. Results of the study appear online June 2011 in the journal Animal Behaviour.