Singing Mice Top The Charts

Maybe singing mice (Scotinomys teguina) wouldn’t make it to Hollywood in America’s Got Talent, but they put on a good show. Males of these diminutive Neotropical rodents sing by producing a series of trills when attracting mates (Figure 1). Like some birds, singing mice take short breaths between notes, and can modulate the frequency by changing the size of their mouth opening (audio file). Females are attracted to the “love songs” of certain males. Bret Pasch at the University of Florida, who has been studying sing mice in the lab, is interested in understanding what vocal cues females use to choose their mates (Pasch et al., 2011). Is it the range, frequency, or stamina that make one male’s song a winner?

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Figure 1. A male singing mouse (Scotinomys teguina). (From Bret Pasch)

According to Pasch, “What makes a great performance is how rapidly males can repeat notes while maintaining a large range of frequencies of each note.” In other words, the higher the frequency it uses, the slower the speed of the trills. These physical limitations on vocal performance mean that females should be able to determine the male’s physical quality by the frequency and speed of its songs.

Pasch and his colleagues were also able to show that male sex hormones had an influence on male song performance. They manipulated the androgen hormone levels in males by implanting excess testosterone in one group of males and removed testosterone (via castration and an empty implant) in another group. The males no longer able to produce testosterone produced slower trills with a smaller range of frequencies that were not considered sexy by female singing mice. In contrast, those males administered excess testosterone were able to maintain a normal vocal performance.

Next, Pasch and his team took normal mouse songs and altered them electronically, producing super appealing songs with more notes per second than normal. Females were placed in a test arena with two speakers and given a choice between normal songs and the enhanced songs (Figure 2). Females approached the speaker with the enhanced song more quickly and stayed near that speaker longer (compared to speakers emanating the normal male song). Thus, females can judge male quality by their songs, something that has not been demonstrated in mammals before.

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Figure 2. (Top) The experimental arena and the spectrograms of slow a and a fast song used in the trials. (Bottom) Female responses to experimental male trills measured as the mean time spent near slow and fast songs. (From Pasch et al., 2011)

Video of a male singing mouse in full voice. Filmed at 100 frames per second and played back at 30 frames per second.
Video


References
Pasch, B., George, A., Campbell, P., & Phelps, S. (2011). Androgen-dependent male vocal performance influences female preference in Neotropical singing mice Animal Behaviour, 82 (2), 177-183 DOI: 10.1016/j.anbehav.2011.04.018