| Summary: | Animals representing a wide range of taxonomic groups are known to select specific food combinations to achieve a nutritionally balanced diet. The nutrient balancing hypothesis suggests that, when given the opportunity, animals select foods to achieve a particular target nutrient balance, and that balancing occurs between meals and between days. For wild ruminants who inhabit landscapes dominated by human land use, nutritionally imbalanced diets can result from ingesting agricultural crops rich in starch and sugar (non-structural carbohydrates, NC), which can be provided to them by people as supplementary feeds. Here, we test the nutrient balancing hypothesis by assessing potential effects that the ingestion of such crops by Alces alces (moose) may have on forage intake. We predicted that moose compensate for an imbalanced intake of excess NC by selecting tree forage with macro-nutritional content better suited for their rumen microbiome during wintertime. We applied DNA metabarcoding to identify plants in faecal and rumen content from the same moose during winter in Sweden. We found that the concentration of NC-rich crops in faeces predicted the presence of Picea abies (Norway spruce) in rumen samples. The finding is consistent with the prediction that moose use tree forage as a nutritionally complementary resource to balance their intake of NC-rich foods, and that they ingested P. abies in particular (normally a forage rarely eaten by moose) because it was the most readily available tree. Our finding sheds new light on the foraging behaviour of a model species in herbivore ecology, and on how habitat alterations by humans may change the behaviour of wildlife. Funding provided by: Swedish Research Council for Environment Agricultural Sciences and Spatial Planning ROR ID: https://ror.org/03pjs1y45 Award Number: 2016-01140 Funding provided by: Swedish Environmental Protection Agency ROR ID: https://ror.org/02y7nf053 Award Number: 13/274 and 2020-00108 Funding provided by: Södra Skogsägarna (Sweden) ROR ID: ...
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