Abstract: Across many vertebrate and invertebrate taxa, acoustic communication is believed to provide information about both the phenotype of the signaler and the signaler’s behavioral intent. In songbirds, vocalizations play a vital role in both aggressive and courtship interactions, and this dual function is thought to have given rise to distinct songs classes within several songbird species. In temperate passerine species it is not uncommon for males to have loud, high amplitude songs (~85-90 dB) and soft, low amplitude songs (55-65 dB) in their repertoire. Although high-amplitude song has historically received greater examination, the function and content of both high and low amplitude songs as it relates to each species is largely unknown. In Dark-eyed Juncos, males sing two distinct song classes at varying amplitudes: high amplitude long-range song (LRS), low amplitude soft long-range song (sLRS), and low amplitude short-range song (SRS). In this experiment, I asked whether male Dark-eyed juncos respond differently to a simulated territorial intrusion (STI) of these three song classes when their mate is fertile. Males responded most strongly to SRS, spending significantly more time near the speaker and exhibiting greater activity during SRS playback. Males responded equally to sLRS and LRS, with significantly fewer flights and less time spent near the speaker than during SRS playback.  SRS, unlike LRS and sLRS, is predominately sung during courtship, thus an intruder singing SRS would potentially signal a greater threat to the focal male’s fitness than sLRS or LRS, which may explain the stronger response to SRS.