Memory for a day: Olfactory place episodic-like memory for dung droppings by the domestic horse (Equus ferus caballus)

The domestic horse (Equus ferus caballus) makes dung deposits to form "stud-piles" and investigates dung droppings more generally, suggesting that dung contains species-relevant communicative information. This natural behavior provides a behavior with which to examine a species-typical form of memory used by horses in relation to their social behavior. Horses were video recorded in indoor and outdoor riding arenas as they were lightly taken on a lead line to experimenter-determined objects or dung-piles. Frame-by-frame video analysis was used to measure sniffing duration and spatial memory of dung dropping visitations. Horses readily approached and sniffed dung for longer durations than they sniffed other objects. They always approached dung at new locations, made head movements across the extent of dung-piles as they sniffed, showed no preference in the nostril directed to the target, and might blink during sniffing and always blinked when disengaging from sniffing. Horses did remember dung visited withing a day by reducing visits and sniff duration but displayed little retention between days. The results are discussed in relation to the idea that this form of episodic-like memory is time limited because it competes with safety-related behavior related to horse movement within foraging areas.