Line transects at sea
Away from nesting colonies, seabirds are frequently surveyed by transect from a ship (Tasker et al. 1984; Komdeur et al. 1992; Briggs et al. 1995; Bibby et al. 2000). Seabirds present particular problems because they are often recorded in flight, and their speed of flight in relation to the speed of the ship through the water and direction of flight relative to that of the ship influence the results markedly. In addition, some birds are attracted to boats, whereas others avoid them, and general viewing conditions are often difficult against the sea surface. The sophisticated methods used on land can generally not be replicated at sea, so surveys tend to focus on indices of relative abundance and have caveats attached. By standardising the count methods, it is at least possible to draw comparisons between different areas and different studies.