SummaryA considerable variety of Indonesian avifauna is forced into the domestic and international pet trade, where the majority of individuals are caught in the wild. To monitor the volume and development of the trade and to evaluate the threat status of the traded species, bird market surveys are usually performed. The most commonly used monitoring technique is the “Direct Counting Method – DCM”, i.e. the counting of openly displayed individuals offered for sale. In this study, we evaluate the reliability of the outputs that DCM delivers by conducting regular long-term bird censuses at two of the main animal markets in Medan (Sumatra, Indonesia) involving 10 major local vendors specialising in the Sumatran Laughingthrush (Garrulax bicolor; SL), our target species. Both markets were visited from March to December 2015 with three different survey intervals (one, two and four visits per month). In total, according to DCM, we recorded up to 461 SL individuals offered for sale. However, a comparison of the monthly logs recorded directly by the vendors during the same period revealed that DCM only uncovered a negligible proportion of the total trade. Specifically, we detected only 4.6%, 8.1% and 16.1% of the traded SL individuals in relation to the set survey intervals. While the numbers of recorded SL individuals according to DCM and the three survey intervals were significantly interrelated, none of them correlated with the real numbers of traded birds provided by the vendors. Our results suggest that census-based market data are underestimated, and represent an unknown proportion of true trade volumes, regardless of the intensity of visits. In order to obtain reliable data and prevent the underestimation of the volume of trade, we recommend of undisclosed monitoring of markets and the engagement of trusted individuals with a past personal interest in this field or, if possible, the vendors themselves.

中文翻译：

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基于视觉的动物贸易普查结果的可靠性如何？一个涉及苏门答腊笑鸫双色雀鹛市场监测的案例研究

总结相当多的印度尼西亚鸟类被迫进入国内和国际宠物贸易，其中大多数个体是在野外捕获的。为监测贸易量和发展并评估贸易物种的威胁状况，通常会进行鸟类市场调查。最常用的监控技术是“直接计数法——DCM”，即对公开展示的出售个人进行计数。在这项研究中，我们通过在棉兰（印度尼西亚苏门答腊）的两个主要动物市场进行定期的长期鸟类普查来评估 DCM 提供的产出的可靠性，其中涉及 10 家专门从事苏门答腊笑嘴鹬的当地主要供应商（蓑衣双色; SL)，我们的目标物种。两个市场在 2015 年 3 月至 12 月期间以三种不同的调查间隔（每月一次、两次和四次访问）进行了访问。根据 DCM 的数据，我们总共记录了多达 461 名 SL 个人出售。然而，对同期供应商直接记录的月度日志的比较显示，DCM 仅发现了总交易量的微不足道的一部分。具体来说，在设定的调查间隔内，我们仅检测到 4.6%、8.1% 和 16.1% 的交易 SL 个人。虽然根据 DCM 和三个调查间隔记录的 SL 个体数量显着相关，但它们都与供应商提供的交易鸟类的实际数量无关。我们的结果表明，基于人口普查的市场数据被低估了，并且代表真实贸易量的未知比例，无论访问强度如何。为了获得可靠的数据并防止低估交易量，我们建议对市场进行不公开的监控，并让对该领域有过个人兴趣的可信赖的个人参与，或者如果可能的话，让供应商自己参与。