Data from: Determinants of elephant foraging behavior in a coupled human-natural system: is brown the new green?

1. Crop raiding by wildlife poses major threats to both wildlife
conservation and human wellbeing in agro-ecosystems worldwide. These
threats are particularly acute in many parts of Africa, where crop raiders
include globally threatened megafauna such as elephants, and where
smallholder agriculture is a primary source of human livelihood. One
framework for understanding herbivore feeding behavior, the
forage-maturation hypothesis, predicts that herbivores should align their
movements with intermediate forage biomass (i.e., peak green-up); this
phenomenon is known as “surfing the green wave.” Crop-raiding elephants,
however, often consume not just foliage, but also fruits and tubers (e.g.,
maize, potatoes), which generally mature after seasonal peaks in
photosynthetic activity. Thus, although elephants have been reported to
surf the green wave in natural habitats, they may utilize a different
strategy in cultivated landscapes by selecting crops that are “browning
down.” 2. We sought to understand the factors that underpin movement of
elephants into agricultural landscapes. 3. In Mozambique’s Gorongosa
National Park, we used movement data from GPS-collared elephants, together
with precipitation records, remotely sensed estimates of landscape
greenness (NDVI), DNA-based diet analysis, measurements of plant
nutritional quality, and survey-based metrics of crop availability to
understand spatiotemporal variation in elephant crop-raiding behavior. 4.
Elephants tracked peak NDVI while foraging inside the Park. During the dry
season, however, when NDVI within the Park declined and availability of
mature crops was high, crop-raiding increased dramatically, and elephants
consistently selected crop plants that were browning down while foraging
in cultivated landscapes. Crops contained significantly higher digestible
energy than wild food plants, but comparable (and sometimes lower) levels
of digestible protein, suggesting that this foraging strategy maximized
energy rather than protein intake. 5. Our study is the first to combine
GPS tracking data with high-resolution diet analysis and community-based
reporting of crop availability to reveal fine-scale plasticity in foraging
behavior of elephants at the human-wildlife interface. Our results extend
the forage-maturation hypothesis by showing that elephants surf waves of
plant brown-down in cultivated landscapes. These findings can aid efforts
to reduce human-elephant conflict by enabling wildlife managers to
prioritize mitigation actions in time and space with limited resources.

1. 野生动物盗食作物对全球农业生态系统中的野生动物保护及人类福祉均构成重大威胁。这类威胁在非洲许多地区尤为严峻——当地盗食作物的动物包括大象等受全球威胁的巨型动物群，而小农农业是人类生计的主要来源。“饲草成熟假说（forage-maturation hypothesis）”是理解草食动物取食行为的框架之一，该假说预测草食动物的活动应与中等饲草生物量（即植被峰值生长期）同步，这一现象被称为“绿浪冲浪（"surfing the green wave"）”。然而，盗食作物的大象不仅取食叶片，还会食用果实和块茎（如玉米、土豆），而这些作物通常在光合活性季节性峰值后成熟。因此，尽管有报道称大象在自然栖息地会“绿浪冲浪”，但它们在耕作景观中可能采取不同策略，即选择“正在枯黄”的作物。
2. 我们旨在探究大象进入农业景观活动的驱动因素。
3. 在莫桑比克的戈龙戈萨国家公园，我们整合GPS项圈大象的移动数据、降水记录、遥感估算的景观绿度（NDVI）、基于DNA的饮食分析、植物营养质量测定以及基于社区的作物可获得性指标，以解析大象盗食作物行为的时空变化规律。
4. 大象在公园内取食时会追踪NDVI峰值。但在旱季，当公园内NDVI下降且成熟作物可获得性较高时，盗食作物行为显著增加，此时大象在耕作景观中持续选择正在枯黄的作物。作物的可消化能量显著高于野生食物植物，但其可消化蛋白质含量与野生植物相当（有时更低），这表明该取食策略旨在最大化能量摄入而非蛋白质摄入。
5. 本研究首次将GPS追踪数据、高分辨率饮食分析与社区报告的作物可获得性相结合，揭示了人兽界面处大象取食行为的精细尺度可塑性。我们的结果拓展了饲草成熟假说——证实大象在耕作景观中会“冲浪枯黄浪”。这些发现可为野生动物管理者提供支持，使其能在资源有限的情况下，按时间和空间优先级实施缓解措施，从而减少人象冲突。