Bird predation experiments in tropical agroforestry landscapes of the Napu Valley in Central Sulawesi, Indonesia

We performed bird predation experiments (dummy experiments), using artificial prey and bird community data to investigate the importance of predator diversity vs. predator identity in cacao agroforestry landscapes. All sample sites were situated at the northern tip of Napu Valley in Central Sulawesi, Indonesia. After an initial mapping of the study area, we selected 15 smallholder cacao plantations as sites for our exclosure experiments in March 2010. For our predation experiment, we selected 10 (out of 15) study sites and 5 cacao trees per site for the application of artificial prey for birds (dummy caterpillars made of plasticine). Our study trees (numbered from 1 to 5 per site) were randomly chosen and we kept spacing of at least two unmanipulated cacao trees between two study trees to avoid clumped distribution. To quantify both daytime/diurnal predation and night-time/nocturnal predation (e.g. birds vs. bats), we applied 7 caterpillar dummies on all study trees and controlled them for predation marks in the early morning (05:00-06:00 am), in the evening (17:00-18:00 pm) and in the early morning on the next day (completing one survey round). In total, we performed four survey rounds per study site (in June and July 2011). The caterpillar dummies were always applied in the same order and on three different parts of each cacao study tree: One 'control dummy' (located on first branching of the cacao tree); 3 'branch dummies' (located on one main branch coming from first branching; 20-25 cm between single dummies) and 3 'leaf dummies' (3 medium aged cacao trees adjacent to main branch were selected and single dummies placed in the center of each cacao leaf). The different positions were chosen to control for different foraging modes of predators (e.g. branch gleaners versus leaf gleaners). During day- and nighttime surveys, we controlled if the dummy caterpillars were still present in their original position, if they were absent and could not be relocated on the ground or if they were fallen to the ground, but could still be recorded. Eaten dummies were counted as 1 mark usually, except for those dummies, where two or more different kind of arthropods had eaten parts of the dummy (2 marks or more). Other predation marks were added to this number. For each dummy, we counted the total number of different predation marks. […]

本研究开展鸟类捕食模拟实验（dummy experiments），采用人工猎物与鸟类群落数据，旨在探究可可农林景观中捕食者多样性与捕食者身份的相对重要性。所有采样点均位于印度尼西亚中苏拉威西省纳普谷北端。在对研究区域进行初步测绘后，我们于2010年3月选取了15处小农经营的可可种植园作为围栏排除实验（exclosure experiments）的样地。针对本次捕食实验，我们从15处样地中选取10处，并在每处样地中选取5棵可可树，用于放置鸟类人工猎物——即橡皮泥制作的模拟毛虫（dummy caterpillars made of plasticine）。本次选取的研究树（每处样地编号1至5）均为随机抽取，且确保每两棵研究树之间至少间隔2棵未进行实验处理的可可树，以避免样树分布出现聚集。为量化日间（diurnal）与夜间（nocturnal）的捕食情况（如鸟类与蝙蝠的捕食差异），我们在每棵研究树上放置7个模拟毛虫，并分别于清晨（05:00-06:00）、傍晚（17:00-18:00）以及次日清晨完成一轮调查后，检查猎物的捕食痕迹。每处样地共计开展四轮调查（均在2011年6月与7月期间）。模拟毛虫的放置顺序固定一致，且均布置在每棵研究可可树的三个不同部位：1个「对照模拟物」（位于可可树的一级分枝处）；3个「枝条模拟物」（取自一级分枝分出的主枝条，单个模拟物之间间隔20-25厘米）；以及3个「叶片模拟物」（选取主枝条旁的3棵树龄中等的可可树，将单个模拟物置于每片可可叶的叶心处）。选取这三种不同的放置位置，是为了控制捕食者不同的觅食模式（如枝条拾食者与叶片拾食者的差异）。在日间与夜间的调查过程中，我们会记录以下三种情况：模拟毛虫仍处于初始放置位置；毛虫失踪且无法在地面找到；或是毛虫掉落至地面但仍可被观测到。通常情况下，被取食的模拟毛虫计为1个捕食痕迹；但若有两种及以上不同节肢动物啃食过该模拟物，则计为2个及以上痕迹，其余捕食痕迹亦计入总数。针对每个模拟物，我们统计其上出现的不同捕食痕迹的总数。[…]