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 signi®cantly 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 in¯uence the population dynamics of both wild boar and small mammals.

Scatter hoarding and cache pilferage by superior competitors: an experiment with wild boar, Sus scrofa

“…Wild boar are known to have a very diverse diet, which certainly includes animal matter, ranging from insects and worms to mice and voles, and they even scavenge around the carcasses of larger animals (Briedermann, 1986). It is thus not unlikely that wild boar form a direct threat to the survival of wood mice, and as a consequence, wood mice might have adjusted their hoarding patterns so that the risk of predation by wild boar, rather than the risk of pilferage, is minimized (Focardi et al, 2000;Muñoz & Bonal, 2007;PuertaPiñero et al, 2010). Generally, larder hoards are connected to the underground burrow system of the hoarder and are usually located near the hoarder's nest, whereas scatter hoards are created from the soil surface, and are usually not connected to the burrow system of the hoarder (Jennings, 1975;Vander Wall, 1990).…”

“…The wild boar is a medium-sized (50e200 kg) ungulate that is regarded as an important competitor to seed-hoarding rodents in forests and woodlands (Focardi et al, 2000;Gomez et al, 2003). The wild boar is one of the most widespread ungulates in the world.…”

“…Acorns are a particularly dominant food in autumn when they have been freshly shed and are abundantly available on the forest floor (Elston & Hewitt, 2010;Massei & Genov, 2004), but also in mid-and late winter when very few acorns remain on the forest floor (Den Ouden et al, 2005;Groot-Bruinderink et al, 1994;Muñoz & Bonal, 2007). This suggests that in winter, wild boar actively search for and pilfer acorn caches created by hoarders such as the wood mouse (Borchert, Davis, Michaelsen, & Oyler, 1989;Den Ouden et al, 2005;Focardi et al, 2000;Gomez et al, 2003;Herrera, 1995). Wood mice play an important role as seed predators and dispersers of acorns in Europe.…”

“…Briedermann, 1986) with a strong preference for acorns (e.g. Focardi, Capizzi, & Monetti, 2000;Groot-Bruinderink, Hazebroek, & Vandervoot, 1994;Herrero, García-Serrano, Couto, Ortuño, & García-Gonzalez, 2006;Schley & Roper, 2003), which intensely competes for acorns with food-hoarding animals such as wood mice (e.g. Gomez, Garcia, & Zamora, 2003;Muñoz & Bonal, 2007;PerezRamos & Maranon, 2008).…”

“…Clarke & Kramer, 1994;Den Ouden, Jansen, & Smit, 2005;Jenkins & Breck, 1998;Jennings, 1975;Jensen & Nielsen, 1986;Lu & Zhang, 2005, and that they can vary depending on wild boar presence (e.g. Focardi et al, 2000;Muñoz & Bonal, 2007;Muñoz, Bonal, & Díaz, 2009;Puerta-Piñero et al, 2010).…”