Advantages and disadvantages of line transects
Line transects can be undertaken at any time of year, on land, on sea or in the air. Line and point transects each have their own strengths and weaknesses (Table 9.2) and it is important that the methods are matched carefully with the survey objectives. Line transects are suited to large areas of homogeneous habitat, and are particularly useful where bird populations occur at low density. Because most birds are detected by song or call, a high level of observer experience is required. Estimates of density can be calculated using distance-sampling techniques. The area sampled by a line transect increases linearly away from the transect line; thus errors in detecting birds close to the observer and in distance estimation are less likely to bias density estimation than is the case with point counts. Random allocation of transect routes can be particularly difficult in some habitats and in some terrain. Because the observer is continually on the move, identification can be difficult and cryptic birds can easily be missed. The high costs of transects at sea can be reduced by observing from ships involved in other activities (though this may introduce some biases). Transects from the air are sometimes too quick to allow precise counts and the identification of some species, their age and sex.
Advantages and disadvantages of line transects
Line transects can be undertaken at any time of year, on land, on sea or in the air. Line and point transects each have their own strengths and weaknesses (Table 9.2) and it is important that the methods are matched carefully with the survey objectives. Line transects are suited to large areas of homogeneous habitat, and are particularly useful where bird populations occur at low density. Because most birds are detected by song or call, a high level of observer experience is required. Estimates of density can be calculated using distance-sampling techniques. The area sampled by a line transect increases linearly away from the transect line; thus errors in detecting birds close to the observer and in distance estimation are less likely to bias density estimation than is the case with point counts. Random allocation of transect routes can be particularly difficult in some habitats and in some terrain. Because the observer is continually on the move, identification can be difficult and cryptic birds can easily be missed. The high costs of transects at sea can be reduced by observing from ships involved in other activities (though this may introduce some biases). Transects from the air are sometimes too quick to allow precise counts and the identification of some species, their age and sex.
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