Get off my back: vibrational assessment of homeowner strength

Animals may use a variety of sensory modalities to assess ownership and resource holding potential (RHP). However, few studies have experimentally tested whether animals can assess these key variables through a purely vibrational modality, exclusively involving substrate-borne vibrations. Here we studied social terrestrial hermit crabs (Coenobita compressus), where competitors assess homeowners by climbing on top of a solid external structure—an architecturally remodelled shell home, inside of which the owner then produces vibrations. In the field, we used a miniature vibratory device, hidden within an empty shell, to experimentally simulate a ‘phantom owner’, with variable amplitudes of vibration representing different levels of homeowner strength. We found that assessors could use these vibrations to deduce the owner’s RHP: for strong vibrations (indicative of a high RHP owner) assessors were least likely to escalate the conflict; for weak vibrations (indicative of a low RHP owner) as...