PDF(Pubmed)
Abstract：
Dimensions of body size are an important measurement in animal ecology, although they can be difficult to obtain due to the effort and cost associated with the invasive nature of these measurements. We avoid these limitations by using camera trap images to derive dimensions of animal size. To obtain measurements of object dimensions using this method, the size of the object in pixels, the focal length of the camera, and the distance to that object must be known. We describe a novel approach of obtaining the distance to the object through the creation of a portable distance marker, which, when photographed, creates a \"reference image\" to determine the position of the animal within an image. This method allows for the retrospective analysis of existing datasets and eliminates the need for permanent in-field distance markers. We tested the accuracy of this methodology under controlled conditions with objects of known size resembling Felis catus, our study species, validating the legitimacy of our method of size estimation. We then apply our method to measure feral cat body size using images collected in Tasmania, Australia. The precision of our methodology was evaluated by comparing size estimates across individual cats, revealing consistent and reliable results. The average height (front paw to shoulder) of the feral cats sampled was 25.25 cm (CI = 24.4, 26.1) and the average length (base of tail to nose) was 47.48 cm (CI = 46.0, 48.9), suggesting wild feral cats in our study area are no larger than their domestic counterparts. Given the success of its application within our study, we call for further trails with this method across a variety of species.
摘要：
体型是动物生态学中的一个重要指标,尽管由于与这些测量的侵入性相关的努力和成本，它们可能难以获得。我们通过使用相机陷阱图像来导出动物大小的尺寸来避免这些限制。要使用此方法获得物体尺寸的测量值，对象的大小（以像素为单位），摄像机的焦距,到那个物体的距离必须是已知的。我们描述了一种通过创建便携式距离标记来获得到对象的距离的新颖方法，which,拍照时，创建“参考图像”以确定动物在图像中的位置。此方法允许对现有数据集进行回顾性分析，并消除了对永久性场内距离标记的需求。我们在受控条件下使用类似于Feliscatus的已知大小的物体测试了该方法的准确性，我们研究的物种，验证我们的尺寸估算方法的合法性。然后，我们使用我们的方法使用塔斯马尼亚收集的图像来测量野猫的体型，澳大利亚。我们的方法的准确性是通过比较个体猫的大小估计值来评估的，揭示一致和可靠的结果。采样的野猫的平均高度（前爪到肩膀）为25.25厘米（CI=24.4，26.1），平均长度（从尾巴到鼻子的底部）为47.48厘米（CI=46.0，48.9），表明我们研究区域的野生野猫并不比它们的家养猫大。鉴于其在我们研究中的应用成功，我们呼吁用这种方法在各种物种中进一步探索。
