Reproductive state alters vocal characteristics of female North American red squirrels (Tamiasciurus hudsonicus).

This article investigates whether female North American red squirrels (Tamiasciurus hudsonicus) use vocalizations to advertise their estrous state during their narrow reproductive window. Analyzing spectral and temporal properties of female territorial rattle calls recorded from known reproductive states over three years, the study found no distinct vocal changes specifically associated with estrus. However, significant alterations in vocal characteristics, including increased fundamental frequency and entropy, were observed during late pregnancy, marking the first evidence of vocal changes linked to pregnancy in a nonhuman mammal. The findings suggest that while female rattles convey information about reproductive condition and body mass, estrus signaling likely relies on multimodal communication, combining chemical cues with vocalizations for individual identification.