Abstract
Distance sampling, a widespread method in ecology, can be applied to estimate seabird abundance from a radar detection image. As the radar was placed on the seashore, the detections were not equally spread in the radar image, but clustered at the side of the sea. Sector and radial method are two primary methods to get samples from the whole image by collecting the data that were detected in the sectors or on the radial lines, and different sub-sampling methods would lead to different errors of the estimations. This paper builds two models respectively on sector data and radial data based on the assumption that the birds are uniformly distributed horizontally in this area, and uses this model to calculate the seabird density with a given example of radar detection as well as to compare the errors between these two methods. The seabird density estimated with sector data is 987 per square kilometer with large errors coming from the nonuniform patterns of birds. While, combined with the deviation mainly caused by the size of birds, the radial method achieved a density of 876 objects per square kilometer. Considering the nonuniform patterns for the sea birds, radial method is the optimal method to give a stable and reliable measurement and estimation the bird abundance, especially with a modified model where the size of bird taken into account. This radial sampling method can substitute to the method that takes all the detections of the radar image into account in estimating seabird abundance.