Pigs rely on spatial rather than numerical cues in an ordinal foraging task

Animals master various numerical tasks. Among numerical abilities, ordinality enables animals to identify an item on the basis of its position in a sequence (e.g. selecting the second out of six), a skill crucial for navigation, documented in species such as domestic chicks, fish and honey bees. Domestic pigs, Sus scrofa domesticus , exhibit advanced spatial and navigation skills. However, their ability to use ordinal information remains largely unexplored. Here, we trained 16 free-ranging Kune Kune pigs in an ordinal task. Seven pigs learned to select the second, and nine pigs the fifth bowl in a sagittal sequence of six identical bowls. When the sequence displacement was identical to the training one (sagittal test), both groups significantly preferred the previously reinforced bowl in the absence of visual or odour cues. When the distances between the bowls were manipulated, so that the ordinally correct and the spatially correct bowl did not coincide (ordinal–spatial incongruence test), pigs relied on spatial cues. Some individuals potentially relied on ordinality, suggesting that pigs can use ordinal information even though spatial information use predominates. When the sequence was rotated by 90°, so that it was oriented frontoparallel with respect to the pig's starting position (frontoparallel test), both groups preferentially approached the second bowl on the right side of the arena, hinting at hemispheric specialization for food-related and/or spatial tasks. Future studies should follow up on the relevance of, and preference for, numerical and spatial cues in pigs as well as on the origins of pigs' right-side preference in ordinal foraging tasks.