Fruit consumption in migratory passerines is limited by water ingestion rather than by body water balance

Many insectivorous passerines become frugivorous during migration. Because water may facilitate the digestion of dry fruits, some passerines may benefit from staging in stopover sites that offer access to drinking water. In autumn, water consumption by Blackcaps (Sylvia atricapilla) staging in Israel was found to induce a shift from insectivory to frugivory. We tested two alternative hypotheses concerning the mechanism facilitating consumption of the relatively dry fruits which are common in this region: (1) Water intake facilitates the passage of fruits within the digestive tract when these two resources are simultaneously ingested, and (2) improved body water balance allows the consumption and ingestion of large amounts of dry fruits. Blackcaps were subjected to five treatments that included temporal separation of water and fruit consumption, as well as subcutaneous water injection to maintain balanced body water in water-deprived birds. Fruit consumption rate was measured daily. We f...

许多食虫性雀形目鸟类（passerines）在迁徙期间会转为食果性。由于水分可促进干果的消化，部分雀形目鸟类或许能从停留于提供饮用水的中途停歇地（stopover sites）中获益。秋季，在以色列停歇的黑顶林莺（Blackcaps, Sylvia atricapilla）的饮水行为被发现可诱导其从食虫性向食果性转变。我们针对促进该区域常见的相对干果类摄食的机制，检验了两个互斥假设：（1）当水分与果实这两种资源被同时摄入时，饮水有助于果实在消化道内的通过；（2）体内水平衡的改善允许大量干果的摄食与吞咽。我们对黑顶林莺实施了五种处理方式，包括将饮水与果实摄食在时间上分离，以及对缺水鸟类进行皮下注水以维持其体内水平衡。每日测量果实摄食率。我们...