Terrestriality in Platyrrhine primates is primarily associated with low arboreal resource availability, low predation risk when on the ground and increased contact time with human observers. To test the relationship between these variables and ground use frequency, we studied a group of endangered Coimbra-Filho’s titi monkeys ( Callicebus coimbrai ) in a 14-ha forest fragment in north-eastern Brazil. Terrestriality data were collected on a monthly basis (33 months) using scan sampling procedures from July 2008 to July 2012. Overall, Coimbra-Filho’s titi monkeys were recorded during 0.6% of observation time (113 out of 18,164 scans) on the ground. Most of the time on the ground was spent feeding on young leaves (71 records) and the least amount of time on fruits (14 records). Availability of arboreal foods, rainfall, and time of contact with human observers did not influence overall terrestrial behaviour (ground use). However, the timing and nature of the monkeys’ terrestrial feeding was strongly related to the absence of arboreal fruit ( β -estimate = −3.078) and young leaf ( β -estimate = −3.515) food resources. We suggest that terrestrial feeding by Coimbra-Filho’s titi monkeys could be an adaptation to low arboreal fruit availability and the exploitation of alternative food resources.

中文翻译：

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仅用于紧急情况：科英布拉-菲略氏雀的陆生喂养反映了季节性树栖资源的可用性

Platyrrhine 灵长类的陆生性主要与低树栖资源可用性、在地面上的低捕食风险以及与人类观察者接触时间增加有关。为了测试这些变量与地面使用频率之间的关系，我们在巴西东北部 14 公顷的森林碎片中研究了一组濒临灭绝的科英布拉-菲略猴 (Callicebus coimbrai)。从 2008 年 7 月到 2012 年 7 月，使用扫描采样程序每月（33 个月）收集陆地数据。总体而言，在 0.6% 的观察时间内（18,164 次扫描中的 113 次）记录了科英布拉-菲略猴的地面。在地面上的大部分时间都花在吃嫩叶上（71 条记录），最少的时间花在吃水果上（14 条记录）。树栖食物的可用性、降雨量、与人类观察者接触的时间不影响整体陆地行为（地面使用）。然而，猴子陆生觅食的时间和性质与缺乏树栖果实（β-估计=-3.078）和幼叶（β-估计=-3.515）食物资源密切相关。我们认为，科英布拉-菲略猴的陆生喂养可能是对低树栖水果供应和替代食物资源开发的一种适应。