In birds, a series of fused vertebrae houses the lumbosacral organ (LSO), where the spinal cord expands and transforms in a way that suggests proprioceptive specialization. The LSO evolved in bipedal theropods and is marked by prominent transverse ridges, a dense glycogen body, and lateral accessory lobes. Comparative morphology and computational models have led researchers to hypothesize that the LSO acts as a secondary balance organ that detects motions of the lower body. This balance sensor, located in the hip, may be critical for birds to stabilize their horizontal upper bodies while walking and perching. However, the LSO is difficult to access with electrodes, resulting in a paucity of rigorous sensory physiology characterizing these putative mechanoreceptors. I propose leveraging new advances in molecular techniques and calcium imaging toinvestigate the mechanosensitive capacity of neurons in the LSO. This investigation may reveal convergent mechanisms of balance sensing and spinal proprioception.