Prey availability, and not energy content, explains diet and prey choice of Eastern Curlews Numenius madagascariensis in southern Australia

摘要

Eastern Curlews breed in Siberia in the boreal spring and summer and migrate to Australia in the austral spring and summer. The Eastern Curlew is notable for its very long, decurved bill; this sexually dimorphic characteristic represents approximately 25-30% of total body length. Female curlews have the longest bill of any wader. Diet and prey choice in relation to availability and profitability were examined over two non-breeding periods in Western Port in southern Australia. Diet was determined from direct feeding observations, examination of pellets collected at high-tide roosts (during daytime and night-time) and by following tracks of foraging curlews. Male and female curlews used the intertidal feeding areas differently: females used more sandy areas and males more muddy areas. This difference may be related to sexual dimorphism in bill length and could reflect substantial dietary differences. Tasselled Crab Pilumnus fissifrons was the most common prey, followed by Australian Ghost Shrimp Trypaea australiensis, Two-spined Crab Litocheira bispinosa and Sentinel Crab Tasmanoplax latifrons. The availability of prey was examined in aquaria through examination of burrowing behaviour and other activity patterns in relation to tidal movements and levels of daylight. Prey behaviour explained the greater consumption of male Ghost Shrimps and the differences in diet between day and night. More Ghost Shrimps and Sentinel Crabs and fewer Two-spined Crabs were taken during the day than during night. Prey choice was examined by measuring the calorific values of prey and potential prey species. Generally, curlews took the more energy valuable prey, but prey behaviour and prey availability mostly determined prey choice, not the energetic value of prey.