Case report: first data on the foraging behaviour of velvet scoters (Melanitta fusca) in soft-bottom coastal waters of the southeast Baltic Sea

Abstract

Abstract Background The foraging behaviour of sea ducks has always been difficult to study due to their exclusive occupancy of coastal waters during the wintering season. In this study we investigated the foraging behaviour of seven wintering velvet scoters (Melanitta fusca) in Lithuanian soft-bottom coastal waters by attaching a solar-powered external GPS‐GSM transmitter to each individual bird. This transmitter data allowed us to analyse the dive phase parameters and feeding depths during December 2021 and March 2022. Results The results showed that velvet scoters dived deeper than a 30-m depth, with the dive duration lasting up to 90 s on average. The bottom duration increased rapidly in the first 5 m and then levelled off at around 40 s for deeper waters. The underwater duration varied between 2 and 7.5 h a day. The dive effort (as total underwater time) and the bottom duration of velvet scoters were related to the depth and prey biomass, although both factors were demonstrated to be interdependent. Moreover, the results showed that velvet scoters were less active in December than in March in terms of both average diving duration and diving frequency. The results also confirmed the high diurnal activity of the velvet scoter, although the birds demonstrated night activity in December and not in March. Conclusion This information on the velvet scoter’s foraging behaviour may have important implications for the conservation of the species, and provides new insights into the improvement of conservation measures for the species in the Baltic Sea.