Food hoarding and use of stored food by Rooks Corvus frugilegus

Abstract

Capsule In autumn, Rooks cached large quantities of acorns, which were retrieved during winter. Aims To describe the autumn storing of acorns by Rooks in a natural situation and to quantify the retrieval of acorns during winter. Methods The collection, transportation and caching of acorns were studied during four autumns, and cache retrieval during two winters, in an extensive grassland area of southern Sweden. Results Rooks transported acorns from a few tens of metres up to 4 km from the source oaks and carried a mean number of 3.56 acorns (range 2–7) during outward flights. Permanent grass appeared to be the preferred caching habitat. In winter, 1 to 1.5 acorns per Rook per hour were retrieved during active foraging. Some were re-cached, with a much lower proportion being re-cached in late than in early winter. In snowy conditions Rooks foraged in the grasslands only when the snow cover was broken or very thin, suggesting that they were unable to use their stores in deep snow. Conclusion Observations strongly indicate that Rooks knew the exact location of their caches and probably possess the long-term memory capacity necessary to relocate caches made several months earlier. It is concluded that Rooks are the most specialized food hoarders of the Corvus species.