But the problem with camera traps is that the researcher has to go back to the forest every so often to retrieve those images, and that takes a lot of time, especially if there are dozens or hundreds of these cameras placed in the forest.
这些相机陷阱的问题在于 研究者必须频繁地 回到森林中去取回这些照片， 这花费很多时间， 特别是当森林中 放有数百个照相机时。