Diet of Reed Warblers Acrocephalus scirpaceus at two stopover sites in Morocco during autumn migration

Diet of the Reed Warbler (Acrocephalus scirpaceus) was estimated by means of forced regurgitations of captured individuals during autumn migration at Kerbacha and Sidi Bou Ghaba, two wetland sites located respectively on the Mediterranean and Atlantic coasts in Morocco. Overall, 88 emetic samples were collected and 17 prey taxa were identified from 789 food items with a predominance of wasps (Hymenoptera) and beetles (Coleoptera) at Kerbacha, and ants including alate forms (Hymenoptera) at Sidi Bou Ghaba. Prey diversity and taxonomic distribution differed significantly between the two sites. Birds at Sidi Bou Ghaba had a lower food intake but fed on larger and less mobile prey than at Kerbacha where most diet samples comprised a large number of small flying prey. These between-site differences are assumed to reflect local food availability and may partly explain the different migratory strategies observed. The short stay and high fattening rate of Reed Warblers at Kerbacha can be associated with the high food intake of a few, abundant prey. The longer stopover duration and lower fattening rate at Sidi Bou Ghaba can be associated with higher diet diversity and lower feeding rate suggesting that prey abundance is globally low except for ephemeral patchily distributed food source such as swarms of flying ants, which are extensively exploited by Reed Warblers whenever available.