Do African savanna elephants (Loxodonta africana) eat crops because they crave micronutrients?

Elephants can cause negative consequences for both themselves and for humans by consuming agricultural crops. It is unclear whether savanna elephant crop consumption is merely opportunistic behaviour or related to insufficient quality of natural forage. We analysed the role of vegetation quality on elephant crop consumption. We focused on the role of micronutrients, as natural elephant diets are thought to be insufficient in elements such as sodium and phosporus, which can influence their foraging decisions. For 12 months across four seasons we collected elephant feeding trail data along with tree, grass and crop samples. We investigated how the quality and availability of these items influenced elephant dietary choices across months and seasons. Subsequently, we compared levels of fibre, digestible energy, dry matter intake, and micronutrients, together with secondary compounds (tannins) across the three vegetation groups. As elephants do not make dietary choices based on one component, we also analysed the nutrient balance of food items with right-angle mixture models. The levels of phosphorus, magnesium and dry matter intake corresponded to foraging preference. Compared to trees and grasses, crops contained significantly higher amounts of digestible energy content, dry matter intake, nitrogen, phosphorus, calcium and magnesium. PCA results showed that crops differed in phosphorus and magnesium levels. The right-angle mixture models indicated that except for one tree species, all food items elephants consumed were relatively deficient in phosphorus. The combined results of these analyses suggest a phosphorus deficiency in elephant diet in northern Botswana. Crops, with their high absolute phosphorus levels and dry matter intake, provide an alternative source of phosphorus to reduce the deficiency. This may explain the high intensity of crop consumption in the wet season in our study area. A potential mitigation measure against elephant crop consumption might be to provide supplementary phosphorus sources.