Abstract Tree and grass quality on the African savannah shows seasonal variation, driving mixed-feeding herbivores to switch between browsing and grazing. During this switch, crop consumption could be an attractive alternative to browsing. We analysed elephant diet variability in the Okavango Delta, Botswana, using faecal stable isotope ratios of carbon (δ^13C) and frequencies of elephant crop consumption, to determine the extent to which crop consumption relates to this potential switch. Although elephants did increase their relative grass consumption in the wet season, browse dominated the annual diet. After February, the proportion of grass in the diet dropped considerably, and continued decreasing through April when farmers reported most crop consumption. Generalized Linear Models revealed that the occurrence of elephant crop consumption increased with the proportion of grass consumed and with decreasing grass quality. The proportion of grass in elephant faeces increased with increasing crop consumption intensity. As crop consumption could also be related to nutrient deficiencies in elephant diet, we calculated the total dietary input of nutrients to reveal potential deficiencies. Elephant diet contained insufficient levels of sodium year-round, and insufficient phosphorus from February to July. As the latter coincides with the timing of crop consumption, we consider our results an indication that phosphorus –and potentially sodium - deficiencies, could play a role in elephant dietary choices, including crop consuming behaviour. Further experimental research is required to show whether supplying elephants with supplementary phosphorus and sodium sources could reduce this micro-nutrient deficiency, and could play a role in reducing elephant crop consumption.

中文翻译：

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与作物消费相关的大草原大象饮食转换的时间

摘要 非洲大草原上的树木和草质表现出季节性变化，驱使混食食草动物在浏览和放牧之间切换。在此转换期间，农作物消费可能是浏览的有吸引力的替代方案。我们使用粪便碳的稳定同位素比 (δ^13C) 和大象作物消耗的频率分析了博茨瓦纳奥卡万戈三角洲的大象饮食变异性，以确定作物消耗与这种潜在转变的相关程度。尽管大象在雨季确实增加了它们的相对草食量，但食草占主导地位。2 月之后，饮食中草的比例大幅下降，并持续下降到 4 月，当时农民报告了大部分作物消费。广义线性模型显示，大象作物消耗的发生随着消耗的草的比例和草质量的降低而增加。大象粪便中草的比例随着作物消费强度的增加而增加。由于作物消耗也可能与大象饮食中的营养缺乏有关，我们计算了营养的总饮食输入以揭示潜在的缺乏。大象饮食全年钠含量不足，2 月至 7 月磷含量不足。由于后者与作物消费的时间相吻合，我们认为我们的结果表明磷——以及潜在的钠——缺乏可能在大象的饮食选择中发挥作用，包括作物消费行为。