Preserving for the future the - once widespread but now vanishing - knowledge on traditional pig grazing in forests and marshes (Sava-Bosut floodplain, Serbia).

Background: Traditional knowledge is key for sustainability, but it is rapidly disappearing. Pig keeping in forests and marshes is an ancient, once widespread, now vanishing practice, with a major economic and ecological potential. The knowledge of pig keepers and the foraging activity of pigs are hardly documented.

Methods: We studied the knowledge of traditional pig keepers (svinjars) on wild plants and pig foraging on the Sava-Bosut forest-marsh complex in Serbia. We conducted picture-based interviews about 234 locally common and/or salient plant species, and participatory fieldwork (11 days) and visual observation (21 days) on pig foraging.

Results: 181 wild plant species were known by svinjars and 106 taxa were consumed by pigs. Svinjars knew well and could name most regularly foraged species. 98 species were reported by svinjars as foraged and 56 as not eaten. 28 species were observed by the authors as eaten regularly, while 21 were nibbled and 17 avoided. Contradictory information on foraging was rare both among svinjars (8 species) and between svinjars and researchers (7 species); several of these species were rare. Leaves of 92, fruits or seeds of 21 and 'roots' of 20 species were reported or observed as eaten, usually with high seasonality. Svinjars were overall observant, but knew little about some less salient species (e.g. Veronica, Circaea). The most common forages (reported and/or observed) were fruits (Quercus, fleshy fruits), grasses (Agrostis, Glyceria), herbs (Ranunculus ficaria, Circaea), nutritious 'roots' (Carex spp., Iris), young shrub leaves (Crataegus, Carpinus) and 'tame' plants growing in the sun (Persicaria dubia, Erigeron annuus). Traditional, now extinct pig breeds were reported as less selective and more 'knowledgeable' about plants, as they received less additional fodder. Svinjars learnt their knowledge since childhood, from community members, but long-term personal observations and everyday encounters with pigs were also important sources of knowledge.

Conclusions: A deeper understanding of pig foraging could contribute to using pigs in nature conservation management, resource management and organic farming, and to a better understanding of wild boar foraging. The knowledge of svinjars is a disappearing intangible cultural heritage of European importance. Knowledge holders deserve recognition, and legal and financial support to continue this tradition.