Advertisement vocalizations support home-range defense in the singing mouse.

Alston's singing mice (Scotinomys teguina) are highly vocal Central American rodents that produce structured "songs" (duration: 5-10 s),^1,2,3 often as part of dynamic vocal exchanges with response timing that resembles that observed in human conversation.^4,5,6,7 Although this behavior has been thought to function in both mate attraction^8,9,10,11 and male-male competition,^12,13,14 its precise ethological relevance remains elusive. To address this issue, we developed a semi-natural terrarium for tracking the activity of S. teguina using thermal cameras capable of monitoring the movement of individual mice, even when visually obscured under a shelter. Given the known sex differences in the behavior,^15,16 we focused on the behavior and interactions of males. We found that each mouse produced unique songs^16,17,18 with reliable counter-singing response latencies, allowing for a vocal signature that can be distinguished by conspecifics. Although individual mice sang spontaneously and with remote partners, we found that pairs of mice within the same terrarium rarely engaged in short-latency counter-singing. We used song playback to demonstrate that counter-singing can most robustly be elicited at distances of ∼2 m, demonstrating the tendency of this species to preferentially interact with others in nearby home ranges.¹⁹ Finally, when an "intruder" mouse entered the environment during staged interactions, the resident mouse often responded aggressively by chasing the intruder and broadcasting songs from outside the safety of a shelter. Taken together, our findings indicate that the S. teguina song functions as an announcement of one's home range to nearby conspecifics.