Accessing camera trap survey feasibility for estimating Blastocerus dichotomus (Cetartiodactyla, Cervidae) demographic parameters

ABSTRACT Demographic information is the basis for evaluating and planning conservation strategies for an endangered species. However, in numerous situations there are methodological or financial limitations to obtain such information for some species. The marsh deer, an endangered Neotropical cervid, is a challenging species to obtain biological information. To help achieve such aims, the study evaluated the applicability of camera traps to obtain demographic information on the marsh deer compared to the traditional aerial census method. Fourteen camera traps were installed for three months on the Capão da Cruz floodplain, in state of São Paulo, and ten helicopter flyovers were made along a 13-kilometer trajectory to detect resident marsh deer. In addition to counting deer, the study aimed to identify the sex, age group and individual identification of the antlered males recorded. Population estimates were performed using the capture-mark-recapture method with the camera trap data and by the distance sampling method for aerial observation data. The costs and field efforts expended for both methodologies were calculated and compared. Twenty independent photographic records and 42 sightings were obtained and generated estimates of 0.98 and 1.06 ind/km², respectively. In contrast to the aerial census, camera traps allowed us to individually identify branch-antlered males, determine the sex ratio and detect fawns in the population. The cost of camera traps was 78% lower but required 20 times more field effort. Our analysis indicates that camera traps present a superior cost-benefit ratio compared to aerial surveys, since they are more informative, cheaper and offer simpler logistics. Their application extends the possibilities of studying a greater number of populations in a long-term monitoring.

摘要：种群信息是评估与规划濒危物种保护策略的核心依据。但在诸多场景中，针对部分物种获取此类信息往往存在方法学或资金层面的限制。沼泽鹿（marsh deer）作为一种濒危的新热带界（Neotropical）鹿类，其相关生物信息的获取难度极高。为解决这一难题，本研究对比传统航空普查法，评估了红外相机陷阱（camera traps）在获取沼泽鹿种群信息方面的适用性。本研究在圣保罗州（São Paulo）卡庞达克鲁斯泛滥平原（Capão da Cruz floodplain）布设了14台红外相机，监测时长为3个月；同时沿13公里的航线开展10次直升机航拍，以探查定居的沼泽鹿种群。除统计鹿只数量外，本研究还旨在对记录到的带角雄鹿进行性别鉴定、年龄组划分，并实现个体识别。种群密度估计方面，红外相机数据采用标记-重捕法（capture-mark-recapture）进行分析，航空观测数据则采用距离取样法（distance sampling）开展计算。研究同时计算并对比了两种方法的投入成本与野外工作量。本次研究共获得20次独立拍摄记录与42次目击记录，据此得出的种群密度估计值分别为0.98只/平方公里与1.06只/平方公里。与航空普查法相比，红外相机陷阱可实现对分枝角雄鹿的个体识别，确定种群性比，还能检测到种群中的幼鹿。红外相机陷阱的投入成本较航空普查低78%，但野外工作量却增加了20倍。本研究分析表明，红外相机陷阱的成本效益比优于航空调查，因其可提供更丰富的信息、成本更低且后勤流程更为简便。该方法的应用可为长期监测中开展更多种群的相关研究拓展了可行空间。