Competition for acorns among wild boar (Sus scrofa) and small mammals in a Mediterranean woodland

Abstract

Observations of the rooting activity of wild boar in a holly-oak grove showed that in March–April the decrease of acorns in the diet (31%) was lower than their availability (82%). Moreover the occurrence of deep rooting events remains high despite the low occurrence of grass roots in the diet. These observations suggested that wild boar may exploit hoards of acorns collected by small mammals living in the study area (mainly wood mice Apodemus sp.). In order to test this hypothesis two experimental trials were set up to: (1) investigate whether wild boar were able to locate acorns buried in the ground (range 0–30 cm) and (2) establish if mouse burrows were more likely to be excavated than locations without burrows. The results clearly show that wild boar actively search for buried acorns, mainly in March (59% vs 31% in April and nothing in May) and that burrows are excavated significantly more than locations without burrows (ratio 2:1, respectively). Moreover, locations with burrows are characterized by a decline of rooting activity as a function of the distance from their centre (P = 0.02), which is absent in the control locations (P = 0.74). Our results show that wild boar are able to partly compensate for a reduced above-ground availability of acorns by predating on hoards collected by small mammals. Since this occurs during a critical period for female wild boar when they are giving birth and lactating, this behaviour may strongly influence the population dynamics of both wild boar and small mammals.