Seagull counting on land and from the air – inventory of Herring Gulls (Larus argentatus) and Lesser black-backed Gulls (L. fuscus) using drones and ground surveys on the Amrum Odde

Abstract

A comparison of two breeding-bird census methods was carried out on Amrum for three breeding seasons (2017–2019). Herring Gulls and Lesser Black-backed Gulls were recorded using ‘Method C’ (pair count in non-visible colonies by counting adult birds flying up) and by drone. Both methods are suitable for monitoring the gull colonies and provide similar results in terms of the total number of breeding pairs with different advantages in terms of evaluation speed and species identification. When counting adult birds in flight (Method C), the number of birds and the very short time for counting make species differentiation more challenging. In addition, the method involves a significant disturbance. To minimise uncertainty and disturbance, a large group of people is required for the counts. Using a drone to record breeding birds yields more accurate numbers and at the same time minimises disturbance in the breeding colonies. Compared to method C, it is easier to differentiate between species, based on the drone imagery. The advantage of using drones depends on the target species and the vegetation. Additional inspections of the area may still be necessary. Since 2020, the large gulls breeding at Amrumer Odde in the north of the island have been counted only by drone. Analysing the images is currently still very time-consuming, which causes a time delay in the availability of numbers. The ongoing development of AI-supported programmes will reduce the processing time in the future. Another advantage of drone surveys is that in addition to recording breeding pairs, other relevant parameters, such as habitat elevation models, can be analysed in the context
of the spatial distribution of breeding birds.