Red squirrel gestation length is unchanged by maternal traits, litter composition, or future food availability

Despite considerable research on reproductive timing, factors influencing intraspecific variation in gestation length in wild mammals have received limited attention, largely due to a lack of high-resolution data. We examined potential drivers of gestation length variation in a wild population of North American red squirrels (Tamiasciurus hudsonicus, Erxleben, 1777) in Yukon, Canada. Drawing on 27 years of conception and parturition data, we found that gestation length was highly conserved, with minimal variation (35.4 ± 1.49 days; mean ± SD). Gestation length was unaffected by maternal age, litter size, or litter sex ratio. Likewise, the anticipation of an upcoming food pulse, caused by synchronous conifer seed masting, had no statistically significant influence on gestation length. This finding stands in contrast to other reproductive traits in red squirrels, which are known to shift in response to food pulses. Overall, our results suggest that gestation length in red squirrels is buffered against environmental variability, likely due to stabilizing selection or strong heritability.