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<p>The most obvious behavioral adaptation to environmental conditions is the adjustment of activity budgets and feeding strategies, such as energy maximization (high cost, high return) or time (low cost, low return) minimization, which determines fitness and long-term persistence of species. We studied the activity budgets of two Indonesian colobines (Javan lutungs <i>Trachypithecus auratus</i> inhabiting lowland forests with higher density and silvery lutungs <i>Trachypithecus cristatus</i> inhabiting coastal forests with lower density). We focused on their responses to the variation in the availability of their main diets (leaves, flowers, and fruits) to examine their feeding strategies. We observed the activity of Javan lutungs intermittently for 16 months (2012–2014, 622 h) and of silvery lutungs for 15 months (2018–2021, 577 h). Both lutungs spent a substantial portion of their time resting (34% for Javan lutungs and 46% for silvery lutungs), likely digesting leaf fiber, reflecting their folivorous nature. In contrast, the silvery lutungs spent a lower percentage of time feeding (7% vs. 43%) and a greater percentage of time moving (40% vs. 18%) than the Javan lutungs. When food resources were scarce, Javan lutungs increased the percentage of time spent resting and decreased the percentage of time spent moving, suggesting a time-minimizing strategy. In contrast, silvery lutungs increased the percentage of time they spent feeding, suggesting an energy-maximizing strategy. The intensity of intergroup competition associated with higher density might have caused Javan lutungs in PNR to employ a time-minimizing strategy. Our study suggests that the feeding strategy of <i>Trachypithecus</i> is site-specific.</p>

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Seasonal Variation in Activity Budgets of Indonesian Lutungs (Trachypithecus auratus and T. cristatus) in Response to Food Scarcity

  • 期刊论文

  • 发表日期：

    2025年10月13日

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  • Yamato Tsuji,
  • Muhammad Azhari Akbar,
  • Dyah Perwitasari‑Farajallah,
  • Rizaldi,
  • Kanthi Arum Widayati,
  • Bambang Suryobroto,
  • Kunio Watanabe

摘要

The most obvious behavioral adaptation to environmental conditions is the adjustment of activity budgets and feeding strategies, such as energy maximization (high cost, high return) or time (low cost, low return) minimization, which determines fitness and long-term persistence of species. We studied the activity budgets of two Indonesian colobines (Javan lutungs Trachypithecus auratus inhabiting lowland forests with higher density and silvery lutungs Trachypithecus cristatus inhabiting coastal forests with lower density). We focused on their responses to the variation in the availability of their main diets (leaves, flowers, and fruits) to examine their feeding strategies. We observed the activity of Javan lutungs intermittently for 16 months (2012–2014, 622 h) and of silvery lutungs for 15 months (2018–2021, 577 h). Both lutungs spent a substantial portion of their time resting (34% for Javan lutungs and 46% for silvery lutungs), likely digesting leaf fiber, reflecting their folivorous nature. In contrast, the silvery lutungs spent a lower percentage of time feeding (7% vs. 43%) and a greater percentage of time moving (40% vs. 18%) than the Javan lutungs. When food resources were scarce, Javan lutungs increased the percentage of time spent resting and decreased the percentage of time spent moving, suggesting a time-minimizing strategy. In contrast, silvery lutungs increased the percentage of time they spent feeding, suggesting an energy-maximizing strategy. The intensity of intergroup competition associated with higher density might have caused Javan lutungs in PNR to employ a time-minimizing strategy. Our study suggests that the feeding strategy of Trachypithecus is site-specific.