Pigeons' (Columba livia) spatial reference memory is stable over long retention intervals

Pigeons received training sessions in which a 3 x 3 matrix of pecking keys was lit with red light. Pecking a particular key (but not the other eight keys) produced grain reward on an intermittent schedule. After this key-location discrimination was learned, subjects received occasional, nonrewarded test sessions, followed immediately by a "relearning" session. The time between these test sessions, which comprised a reference memory retention interval, varied from 1 to 30 days. No significant forgetting was found, even at the longest retention interval. This finding stands in marked contrast to typical results for pigeons tested on spatial working memory tasks (such as delayed matching to sample) in which forgetting is rapid. Our findings are consistent with Bond, Cook, and Lamb's (1981) suggestion that the pigeon's foraging ecology has favored the development of proficient reference rather than working memory.