ABSTRACT
Line transect sampling is intended not only for the estimation of the abundance per unit area of rare, mobile, difficult-to-detect animals but also is of value for the study of rare, difficult-to-detect plants, intertidal organisms, and so on (Burnham et al., 1980). The technique is related to variable circular plot sampling and is sometimes called distance sampling (Buckland et al., 2001). With line transect sampling, the basic idea is that an observer moves along a line through a study area, looking to the left and right for the animal or plant of interest. Line transects are walked, flown, or otherwise traversed, and the perpendicular distances to all detected items of interest are recorded. Combining these data with the assumption that all items on the line are detected, it is possible to correct the estimates of abundance per unit area for the items not detected. When an individual of the species of interest is detected, it is recorded, usually together with its distance from the line, because it is assumed that individuals that are far from the line are harder to detect than those that are close. This is one of the specialized ways that ecologists can use to estimate the density or the total number of animals or plants in a study area when it is not possible to simply count all the individuals and the standard sampling methods considered in Chapter 2 are for some reason not practical. For example, if the study area is very large and the species of interest is rare, then a random sample of quadrats in the study area may contain no individuals. However, if a long line is traveled through the area, then some individuals might be detected.
