Liu Tong, Green Angela R, Rodríguez Luis F, Ramirez Brett C, Shike Daniel W
Department of Agricultural and Biological Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America.
Department of Animal Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America.
PLoS One. 2015 Feb 3;10(2):e0113117. doi: 10.1371/journal.pone.0113117. eCollection 2015.
The number of animals required to represent the collective characteristics of a group remains a concern in animal movement monitoring with GPS. Monitoring a subset of animals from a group instead of all animals can reduce costs and labor; however, incomplete data may cause information losses and inaccuracy in subsequent data analyses. In cattle studies, little work has been conducted to determine the number of cattle within a group needed to be instrumented considering subsequent analyses. Two different groups of cattle (a mixed group of 24 beef cows and heifers, and another group of 8 beef cows) were monitored with GPS collars at 4 min intervals on intensively managed pastures and corn residue fields in 2011. The effects of subset group size on cattle movement characterization and spatial occupancy analysis were evaluated by comparing the results between subset groups and the entire group for a variety of summarization parameters. As expected, more animals yield better results for all parameters. Results show the average group travel speed and daily travel distances are overestimated as subset group size decreases, while the average group radius is underestimated. Accuracy of group centroid locations and group radii are improved linearly as subset group size increases. A kernel density estimation was performed to quantify the spatial occupancy by cattle via GPS location data. Results show animals among the group had high similarity of spatial occupancy. Decisions regarding choosing an appropriate subset group size for monitoring depend on the specific use of data for subsequent analysis: a small subset group may be adequate for identifying areas visited by cattle; larger subset group size (e.g. subset group containing more than 75% of animals) is recommended to achieve better accuracy of group movement characteristics and spatial occupancy for the use of correlating cattle locations with other environmental factors.
在利用全球定位系统（GPS）进行动物活动监测时，确定能够代表群体共同特征所需的动物数量仍是一个问题。监测群体中的一部分动物而非所有动物可降低成本和人力；然而，数据不完整可能会导致信息丢失以及后续数据分析出现不准确的情况。在牛的研究中，考虑到后续分析，对于确定群体中需要佩戴仪器的牛的数量，所做的工作很少。2011年，在集约化管理的牧场和玉米残渣地，用GPS项圈以4分钟的间隔对两组不同的牛群（一组由24头肉牛母牛和小母牛组成的混合群体，另一组为8头肉牛母牛）进行了监测。通过比较部分群体和整个群体在各种汇总参数方面的结果，评估了部分群体规模对牛群活动特征和空间占用分析的影响。正如预期的那样，对于所有参数而言，动物数量越多结果越好。结果表明，随着部分群体规模的减小，群体平均行进速度和每日行进距离被高估，而群体平均半径被低估。群体质心位置和群体半径的准确性随着部分群体规模的增加呈线性提高。通过GPS位置数据进行核密度估计，以量化牛群的空间占用情况。结果表明，群体中的动物在空间占用方面具有高度相似性。关于选择合适的部分群体规模进行监测的决策，取决于后续分析中数据的具体用途：较小的部分群体可能足以确定牛群到访的区域；建议采用较大的部分群体规模（例如包含超过75%动物的部分群体），以便在将牛群位置与其他环境因素相关联时，能更准确地获取群体活动特征和空间占用情况。
