Berries to Go: Distinct Passerine Spring Migration Frugivory at a Main Mediterranean Stopover Site

Many animals show phenotypic flexibility in response to a seasonal environment. Especially migratory birds have been found to exhibit striking physiological and behavioural adaptations to overcome the negative impacts of environmental seasonality. Migratory songbirds often show extreme changes in feeding physiology and behaviour before embarking on a migratory flight, including predominantly insectivorous species switching their diet preference to a frugivorous one before autumn migration. Yet, little is known about frugivory during spring migration in temperate zones. In this paper, we report that five songbird species forage on the fruits of two Mediterranean plants, <i>Prasium majus</i> and <i>Rhamnus alaternus,</i> during spring stopover in the Tyrrhenian Sea. Analyses of faecal content showed that fruits of <i>P. majus</i> were generally preferred, with garden warblers (<i>Sylvia borin</i>) having the highest percentage of faecal samples containing seeds of both plants. Availability of ripe <i>P. majus</i> fruits increased over the sampling season and correlated positively with the number of faecal samples containing seeds. Our findings reveal a relevance of fruit at a temperate zone stopover site during spring migration for five passerine species. Frugivory during spring migration may represent an easy means for birds to acquire macronutrients, micronutrients and water. This may be especially important at resource-poor stopover sites and may aid birds' continuation of the northward flight towards their breeding grounds in a timely manner.