Data from: Macronutrient selection of free-ranging urban Australian white ibis (Threskiornis moluccus)

Anthropogenic habitats often provide urban wildlife the opportunity to feed on a range of nutritionally diverse foods, which may ultimately lead to human-wildlife conflict. The Australian white ibis (Threskiornis moluccus) provides an exemplar model for examining the nutritional priorities and constraints of a native vertebrate that is successfully transitioning to an urban specialist. Here, we used field-based feeding trials to investigate the macronutrient preferences of free-ranging ibis in Sydney, Australia. Feeding trials (n = 61) offering three experimental feeds showed that ibis selected significantly more high-carbohydrate (HC) than high-protein (HP) and high-lipid (HL) foods (95% CIHP-HC = −1.115 to −0.709; CIHL-HC = −1.874 to −1.468), and significantly more HP than HL (CIHL-HP = −0.962 to −0.556). The average proportion of macronutrient-derived energy selected by ibis was 25% protein (P; ± 1.1 SE): 23% lipid (L; ± 1.1): 52% carbohydrate (C; ± 1.8). Nutritional geometry suggested that mixtures selected at experimental feeders were substantially higher in C and lower in P than are natural prey (e.g. insects, crustaceans), which were composed primarily of P and L. Compositional log-ratio-based linear models of factors affecting macronutrient proportions selected by ibis showed that: 1) ln(P/C) increased with amount of recent rainfall; and 2) ln(L/C) also increased with rain and had a non-linear relationship with number of birds feeding. Our results suggest that ibis forage for macronutrients rather than energy “per se”, and that their urban foraging is influenced by competition and the environment.人为生境通常为城市野生动物提供了取食多种营养丰富多样食物的契机，而这最终可能引发人兽冲突。澳大利亚白鹮（Threskiornis moluccus）便是理想的模式物种，可用于研究成功转型为城市特化物种的本土脊椎动物的营养偏好与生存限制因素。本研究依托澳大利亚悉尼的野外取食试验，探究了自由活动的澳大利亚白鹮的宏量营养素（macronutrient）偏好。本次共开展61组喂食试验，设置三种实验饵料供白鹮取食：高碳水化合物（high-carbohydrate, HC）、高蛋白（high-protein, HP）与高脂肪（high-lipid, HL）。结果显示，白鹮对HC饵料的选择量显著高于HP与HL饵料（95%置信区间CI_HP-HC = −1.115 至 −0.709；CI_HL-HC = −1.874 至 −1.468），同时对HP饵料的选择量也显著高于HL饵料（CI_HL-HP = −0.962 至 −0.556）。白鹮所选取的宏量营养素供能平均占比为：蛋白质（protein, P）25%（±1.1 标准误（standard error, SE））、脂质（lipid, L）23%（±1.1 标准误）、碳水化合物（carbohydrate, C）52%（±1.8 标准误）。营养几何（nutritional geometry）分析结果表明，实验投喂点中白鹮选取的饵料混合物，其碳水化合物占比显著高于天然猎物（如昆虫、甲壳类），而蛋白质占比则更低；天然猎物主要由蛋白质与脂质构成。针对影响白鹮选取宏量营养素占比的因素，基于成分对数比（compositional log-ratio）的线性模型分析结果显示：其一，蛋白质与碳水化合物的比值自然对数（ln(P/C)）随近期降雨量增加而上升；其二，脂质与碳水化合物的比值自然对数（ln(L/C)）同样随降雨量增加而上升，且与取食白鹮的种群数量呈非线性相关关系。本研究结果表明，白鹮的觅食行为是以宏量营养素为目标，而非单纯以能量为导向；其城市觅食活动同时受到种间竞争与环境因素的调控。