Migrant Birds Are the Main Seed Dispersers of Blackberries in Southern Spain

Between-habitat variation in fruit production and bird attributes enhancing seed ingestion and removal were studied to describe the avian seed-dispersal system of blackberries (Rubus ulmifolius, Rosaceae) in southern Spain. birds were largely responsible for seed dispersal. Among 20 passerine species recorded feeding on fruits, five removed the bulk of seeds: Sylvia arricapilla (29.6% of 897 visits recorded), Erithacus rubecula (15.2%), S. bonn (14.7%), S. rnelanocephala (10.1%) and Turdus merula (7.7%). During an average day 32400 seeds left a parent clone through the activity of these species. production was density-dependent, being maximum in high-density situations. Seed removal (i.e., fruit consumption) from individual clones was dependent on crop , habitat occupied and ripening phenology. Clones ripening a small crop later in the season and/or in low-density habitats had a lower fraction of the crop consumed did those producing huge crops in high density habitats and/or synchronously with autumn bird migration. small, passerine birds presumably contributed to the bulk of seed dispersal because they (1) feed on Rubus fruits extensively, (2) showed high visit rates and removed a very high fraction of the seed crop from parent clones, (3) did not damage the seeds nor drop them beneath the parent clone and (4) performed species-specific flights to apparently safe sites for the plant, thus enhancing its colonizing ability